Manuals of Technology. 
 
 EDITFO BY 
 
 Prof. Ayrton , F.R.S. , and R. Wormell % D. Sc. , M.A. 
 
Cutting Tools 
 
 WORKED BY 
 
 HAND AND MACHINE. 
 
 WITH 
 
 H FOLDING PLATES AND 51 WOODCUTS . 
 
 BY 
 
 ROBERT H. SMITH, ASS.M.I.O.E., 
 
 Profecs^r cf Engineering in the Mason Science College^ 
 Birmingham , forme') ly Pi ofessor of Engineering 
 in the Imperial University , Japan. 
 
 SECOND EDITION. 
 
 CASSELL •& COMPANY, Limited: 
 
 LONDON, PARIS & NEW YORK. 
 
 [all rights reserved.] 
 

PREFACE. 
 
 The aim of this work is educational, and at the same 
 time it is intended as an attempt, at least, to begin the 
 elevation of the art of tool-making from its present entirely 
 empirical to a more scientific position. It has, how- 
 ever, been found possible to make only brief and general 
 references to the principles of strength and stiffness that 
 ought to govern the proportioning of the various parts of 
 machine tools. So far as the author knows, no effort has 
 yet been made to apply methods of exact calculation to the 
 design of the leading dimensions of this class of machines. 
 It is clear that to enable tools to do good work their dimen- 
 sions must be regulated so as to ensure stiffness and not 
 mere strength , while hitherto, in attempts to apply scien- 
 tific calculation to engineering design, the rules for 
 strength have been much too commonly and indiscrimi- 
 natingiy followed, to the neglect of stiffness. It is 
 probable that there will continue to be an unfortunate 
 tendency in this direction, because so long as a machine 
 has strength it “ will do,” that is, it will serve its purpose 
 after a fashion, without leading to positive catastrophe ; 
 whereas it is only those who trouble themselves about 
 refinements which are too often considered superfluous, 
 who recognise that it is tistially only in so far as a 
 machine combines stiffness with strength that it does 
 
VI 
 
 CUTTING TOOLS. 
 
 ivell. Again, it would be impossible within the present 
 limits of this book to develop detailed rules for the 
 proper dimensions of the machines dealt with. The 
 author also regrets that he has been unable to extend 
 the experiments referred to on pages 173 to 181 in 
 time for the publication of the present edition. In 
 the 4 * Proceedings of the lloyal Society’’ for December, 
 1881, Mr. A. Mallock has described a series of interesting 
 observations on lathe turnings made in the Mechanical 
 Laboratory at Cambridge, and has given the most careful, 
 but still incomplete, analysis of the cutting forces in 
 front of the tool edge that has yet been published. 
 In the author’s experiments, carried out in the spring 
 of 1881, the cutting force was measured in the most 
 direct manner, and with very little probable error. 
 The plotted curves, showing the results of each series of 
 experiments, have almost invariably the same character, 
 but this character seems to be so peculiar that no 
 algebraic formula has yet been found to represent it. 
 The author hopes shortly to extend these interesting 
 experiments in the Mechanical Laboratory of the Mason 
 College, and trusts that the law connecting the force with 
 the depth and breadth of the shaving removed will be 
 ultimately discovered. It is evidently upon the magni- 
 tude of this force that all proper calculations made in 
 designing the machine must be based. 
 
 The chief object of the book, however, is educational. 
 It is intended to guide the mechanical student into a 
 correct scientific way of thinking about tools, so that he 
 may be able, aided by practice, to judge intelligently 
 whether a tool is good or bad, to criticise its details, and 
 eventually to design new tools scientifically. It is of 
 
PREFACE. 
 
 Vll 
 
 comparatively little importance that he should know 
 whether the tool is in accordance with the pattern 
 adopted by this or that maker. 
 
 To succeed in this aim as the author would wish, accu- 
 racy and particularity are both essential. In all purely 
 technical subjects, such as that of which this work treats, 
 minutice are of very great importance. For the purpose 
 of training the intellect to deal well with practical things, 
 it is of much more use to think out thoroughly every detail 
 of a single example, than to make a cursory study of the 
 “ general principles 5 ' of a dozen. It has, therefore, been 
 the author’s aim to encourage thoroughness in the con- 
 sideration of the details of the subject. The illustrations 
 taken have seemed to the author those best calculated to 
 give an insight into the general character of tools. As 
 he has deemed it of greater importance to explain fully a 
 few than to mention all kinds of tools, it will be found 
 that several classes of cutting tools have not been treated 
 of. The most important omissions are those of screw- 
 cutting tackle and files. In the hope of sustaining, so 
 far as possible, the interest of the student in what to 
 many seems a dry subject, the author has intentionally 
 adopted an easy lecturing style of writing. 
 
 Every year the number of men who are more or 
 less acquainted with science, and who have a practical 
 connection with manufactures, is increasing, and every 
 year more use is made of the lessons of science in the 
 processes of manufacture. These laudable attempts 
 are, however, difficult, because the common mode of 
 teaching science is to abstract it from every consideration 
 of utility, and it is even not at all uncommon to hear 
 practical usefulness decried as the basest and most un- 
 
ym 
 
 CUTTING TOOLS. 
 
 worthy of motives for scientific research. The author’s 
 belief is exactly the reverse : the highest possible aim 
 and sanction of scientific study are the outcome of comfort 
 and happiness to living creatures that results from it, the 
 general amelioration of the conditions of life in the world. 
 The opposite opinion has among others this result 
 inimical to the interests of pure science itself, namely, 
 that in accordance with it the vastest possible field for 
 true scientific observation is cut off from the view of the 
 scientific student. That field exists in the operations of 
 the manufacturer, which are almost infinite in variety, 
 and which vary and progress continuously. This mag- 
 nificent field of research is watched patiently day by 
 day by millions of intelligent operatives and managers, 
 but in spite of their general intelligence they, as a rule, 
 make no use of their opportunities, because they have 
 either received no scientific education, or else have been 
 taught that science has nothing to do with the common 
 things on which their daily work is expended. If this 
 condition of things were reversed, it is difficult to predict 
 how much more rapid the progress of science might 
 become than it is at present. 
 
 There is an innumerable series of parallel but 
 different physical facts, from any one of which the 
 general fundamental laws of physical science may be 
 learnt almost as well as from any other. The operative 
 in each special craft need hardly go beyond the narrow 
 limits of his own trade to get proof of the most funda- 
 mental and widest branching laws of Nature, provided 
 he has some guide to lead him right. He may hammer 
 them out on the anvil, or he may mould them in the 
 foundry. If they are brought home to his mind by the 
 
PREFACE. 
 
 IX 
 
 facts of his own trade, not only will they gain far greater 
 reality in his conception than if obtained from books only 
 or lecture-table experiments, but at the same time also 
 his work will come to have a far higher and keener 
 interest for him, and the tone of his life will rise from 
 the weariness of drudgery to the healthful enjoyment 
 that is felt in exercising one’s higher faculties. 
 
 It is partly as a contribution to this mode of extend- 
 ing scientific knowledge that the present book has been 
 written, no less so than in the hope of rendering more 
 scientific the efforts at improvement in cutting tools. 
 This method of teaching science is quite a new one, and 
 there are, therefore, no models to follow. The subject of 
 cutting tools is one of the most interesting that could be 
 proposed to a scientific student. It is curious to think 
 what a very large proportion of the whole energy spent in 
 manufacturing operations is spent in some kind of cut- 
 ting, or in the very similar processes of tearing and 
 crushing — it is difficult to draw any distinct line between 
 “ cutting ” and these last-mentioned processes. Even 
 when from cutting operations those only are selected that 
 are in use among engineers, as is done in the present 
 volume, the richness of the field for interesting observa- 
 tion and experiment is quite obvious. If his attempt to 
 explain clearly some elementary matters only leads to 
 some few turners, and planers, and fitters, applying their 
 minds actively to find out something more about what 
 they do every working hour, the author will be quite 
 satisfied with the result of his labours. 
 
 The plan of the book being educational and scientific, 
 it has been deemed best to treat wood and metal tools 
 
X 
 
 CUTTING TOOLS. 
 
 simultaneously, as far as possible, the classification not 
 depending on the material cut so much as upon the mode 
 of cutting. 
 
 In conclusion, the author has to acknowledge his 
 indebtedness to Professor Hart’s “ Werkzeugmaschinen” 
 for some of the illustrations. For others he has to 
 tender his thanks to various manufacturers who have 
 kindly allowed him to use their drawings. For the 
 careful preparation of these drawings he has to acknow- 
 ledge his obligation to Mr. Batten ; and he wishes also 
 publicly to offer his best thanks to the publishers for the 
 liberal way in which they have incurred the expense of 
 the engravings. 
 
PREFACE TO SECOND EDITION. 
 
 On the occasion of the issue of a Second Edition, the 
 Author desires to offer his best thanks to the engineering 
 public and to the press for their kindly appreciation of 
 the effort which he has made to supply a want in 
 technical literature. 
 
 During the short interval since the first appearance 
 of the book, some extension of the use of modern 
 improved workshop machinery has taken place, but no 
 important novelties in the design of cutting tools have 
 been produced. Nevertheless the book has been care- 
 fully revised, and some alterations and additions have 
 been made, with the object of making the meaning of 
 certain passages clearer and of bringing other portions 
 up to date. A chapter has been added embodying the 
 most recent information regarding the qualities and 
 treatment of Tool-Steels. The Index is another new 
 feature which, it is hoped, will increase the utility of 
 this Manual. 
 
 R. H. S. 
 
CONTENTS. 
 
 
 CHAPTER I. 
 
 CHISEL TOOLS FOR WOOD. 
 
 PAGE 
 
 L delations between Chisel Tools — 2. Scientific Classification 
 — 3. Wedges — 4. Wedge Action in Cutting Tools — 5. 
 Mortising Chisel — 6. Axe — 7. Hatchet — 8. Adze — 9. Pen- 
 knife — 10. Paring Chisel — 11. Grinding Wood Tools — 12. 
 Setting Edge Tools — 13. Paring Action — 14. — Power required 
 to Pare Wood — 15. Tools for Metals ... . . 1 
 
 CHAPTER II. 
 
 CHIPPING CHISELS AND HAND PLANES. 
 
 1. Difference from Tools of Chap. I. — 2. General Characteristics — ■ 
 
 3. Cold Chisels — 4. Chipping Hammer — 5. Guidance of 
 Chipping Chisel — 6. Penetration by Chisel-edge — 7. Wood 
 Hand Planes — 8. Guidance of Planes — 9. Difference between 
 Wood Plane and Paring Chisel ...... 21 
 
 CHAPTER III. 
 
 MACHINE PLANES FOR WOOD. 
 
 1. Velocity of Cutting — 2. Classes of Machine Planes — 3. Vertical 
 Spindle Machine — 4. Calculation of Feed — 5. Importance of 
 Correct Setting of Chisels— 6. The Cut on Vertical Cylindrical 
 Surface — 7. Cross Strains through the Machine — 8. Pitch of 
 Chisels in Horizontal Spindle Machines — 9. Ransome and 
 Co.’s Wood planing Machine — 10. Steadying Roller — 11. 
 
 The Feed — 12. Moulding Blades — 13. Tenoning and other 
 Machines .32 
 
 CHAPTER IV. 
 
 SAWS AND MILLING MACHINES. 
 
 1. Difference from Machines of Chap. III. — 2. Saving of Timber 
 by Thin Saws — 3. Saving of Power by Thin Saws — 4. Frame, 
 Band, and Scroll-band Saws — 5. Circular Saws — 6. Forms 
 
XIV 
 
 CUTTING TOOLS. 
 
 PAGE 
 
 of Saw-teetli — 7. Setting Saw-teeth — 8 Inserted Teeth — 
 
 9. Sawdust Space — 10. Cutting Speed and Feed — 11. Horse- 
 power — 12. Cold-iron Saws — 13. Hot-iron Saws— 14. Milling 
 Machines — 15. Machine Vice — 16. Mechanism of Milling 
 Machines — 17. Cutting Speed and Rate of Feed in Milling 
 Machines — 18. Sharpening Milling Cutters — 19. Face-plate 
 Chuck with Milling Cutters — 20. Cutting Angles — 21. 
 Traversing Headstocks for Milling Machines — 22. Improved 
 Milling Cutter . 43 
 
 CHAPTER V. 
 
 PLANING, SHAPING, AND SLOTTING MACHINES. 
 
 1. Planing Tools for Metal — 2. Fixture of Tool or Work — 
 
 3. Action of Planing Tools — 4. Friction between Shaving and 
 Tool — 5. Lubrication and Cooling — 6. Angles of Tool- edge — 
 
 7. Tool-holders — 8. Tool-box — 9. Quick Return Motion in 
 Planing Machines — 10. Acceleration of Momentum at begin- 
 ning of Stroke — 11. Reversible Tool-holders — 12. Systems of 
 Driving Planing Machines — 13. Shaping Machines — 14. Cir- 
 cular Shaping — 15. Slotting Machines : Tool-box — 16. Mode 
 of Driving — 17. Table and Feed Motions — 18. Improvements 
 in Planing Machines 70 
 
 CHAPTER VI. 
 
 LATHES. 
 
 1. Primitive Lathes — 2. Geometrical Character of Turned Work — 
 
 3. Hand and Power Mechanism — 4 Tool-rest for Wood- 
 turning — 5. Tools for Wood-turning — 6. Tool-rest for Metal- 
 turning — 7-9. Mechanism of Slide-rest— 10-12. Feed Motion 
 for Screw-cutting — 13. Headstock — 14. Centre-point — 15-16. 
 Parallel and Conical Bearings in Headstocks — 17-18. Double 
 Gear — 19-20. Loose Headstock — 21. Modes of Driving and 
 Chucking Work — 22. Driving by Face-plates — 23. Driving by 
 Jaw-chucks — 24. Concentric Jaw-chucks — 25. Function of 
 Lathe and Bed — 26. Size of Lathe ; Gap-Lathes — 27. Break 
 Lathes — 28. Face Lathe — 29. Treble Gear — 30. Wheel Lathe 105 
 
 CHAPTER VII. 
 
 CUTTING TOOLS FOR LATHES. 
 
 1-2. Point of Application of Tool — 3. Cutting Face ; Top and 
 Bottom Rake — 4. Cutting Angle — 5. Faulty Formation of 
 Cutting Face — 6. Side-Rake — 7. Straight- edged Tools — 8. Side 
 Tools — 9. Springing of the Tool — 10. Tool-holders — II , 
 Springing of the Work — 12. Back Steady-rest — 13. Capstan 
 Tool-rest and hollow Mandril — 14. Boring Collar — 15. 
 Chasing Tools — 16. Experiments on Cutting Pressure on 
 Tool-point in Lathe— 17. Influence of Cutting Speed on 
 
CONTENTS. 
 
 XV 
 
 PAGE 
 
 Cutting Pressure— 18. Comparative Resistance to Cutting in 
 Different Metals — 19. Influence of Variation of Traverse 
 Feed on Cutting Pressure — 20. Influence of Variation of 
 Depth of Cut on Cutting Pressure — 21. Photographs of 
 Shavings of Cast-iron, Wrought-iron, Steel, and Gun- 
 metal . . • i ..••••• loO 
 
 CHAPTER VIII. 
 
 BORING- AND DRILLING. 
 
 1. Boring and Turning — 2. Difficulty of supporting the Tool in 
 Face-plate Boring— 3. Boring-Bar — 4. Boring large Cylinders 
 — 5. Double-boring Machines — 6. Drilling and Boring — 7. 
 Drilling Tools : Defects of Ordinary Forms — 8. Twisted 
 Drills : Morse Twist Drill — 9. Guidance of Drilling Point : 
 Centring — 10. Other forms of Drills for Metal — 11. Lubrica- 
 tion in Drilling — 12. Construction of Drilling Machine — 13. 
 Different Designs of Table — 14. Arrangement of Feed-Gear — 
 
 15. Other arrangements of Feed-gear — 16. Radial Drilling 
 Machine — 17. Multiple Drilling Machine — 18. Slot Drilling — 
 
 19. Hand Drilling in Wood and Metal; Hand Braces; Ratchet 
 Braces ; Bow Drill 181 
 
 CHAPTER IX. 
 
 PUNCHING AND SHEARING MACHINES. 
 
 1. Similarity between Punching and Shearing — 2. Combined 
 Punching and Shearing Machine— 3. Shearing Machine — 4. 
 Driving Mechanism — 5. Whitworth’s Driving Gear — 6. 
 Hydraulic Punching and Shearing Machine — 7. Multiple 
 Punching Machine — 8. Mode of Rupture by Simple Shear 
 — 9. Mode of Rupture in Punching — 10. Error in the Ordi- 
 nary Calculation of the Strength of Punches — 11. Relation 
 between Shearing and Punching and other Cutting Machines. 210 
 
 CHAPTER X; 
 
 TOOL STEEL. 
 
 1. General Characteristics of Steel — 2. Manufacture of Tool Steel 
 3. Combined Carbon — 4. Silicon — 5. Other Constituents — 
 
 6. Special Brands — 7. Hardening and Tempering — 8. Colour 
 Scale of Temperatures — 9. Various Effects of Sudden Cooling 
 — 10. Different Cooling Substances — 11. Water-Cooling by 
 Evaporation — 12. Lead Bath — 13. Tempering— 14. Cracking 
 and Warping 225 
 
 Index 
 
 . 238 
 
XVI 
 
 CUTTING TOOLS. 
 
 LIST OF PLATES. 
 
 — ■ - frO * — -* 
 
 PAGE 
 
 I. — Milling Machine ..... To face 60 
 
 II. — Planing Machine 90 
 
 III. — Shaping Machine 96 
 
 IV. — Slotting Machine . . . . . ,, 102 
 
 V. — Screw- Cutting and Surfacing Latlio . . „ 114 
 
 VI. — Lathe Headstocks . . . . . ,, 126 
 
 VII. — Pace Lathe . . . . ? . „ 146 
 
 V [II.— Wheel Lathe ,, 150 
 
 IX. — Curves co-ordinating the Cutting Porces 
 exerted by the Points of Turning-tools, 
 with the Breadths of Shavings removed „ 174 
 
 X.-— Curves co-ordinating the Cutting Forces 
 exerted by the Points of Turning-tools, 
 with the Depths of Shavings removed . „ 176 
 
 XI. — Lathe Shavings , , . . . . „ 178 
 
 XII. — Wrought-iron Shaving . . . „ 180 
 
 XIII. — Double-geared Drilling Macliino . . „ 200 
 
 XIV. — Radial Drilling Machine • 
 
 204 
 
Cutting 
 
 WORKED BY HAND AND MACHINE. 
 
 *o» 
 
 CHAPTER I. 
 
 CHISEL-TOOLS FOR WOOD. 
 
 1. Relations between Chisel-tools. — It is easy to re- 
 cognise that there is some considerable resemblance and 
 intimate relation between the modes of action of such 
 tools as the iron wedge for splitting wood, the axe, the 
 adze, the hatchet, the penknife, the paring and mortising 
 chisels, and the spoke-shave. 
 
 2. Scientific Classification. — It is the chief object of 
 science to simplify onr knowledge of the multitude of 
 forms and modes of action which we observe in the 
 things that surround us, and that we use in doing our 
 work, or enjoy in taking our pleasure, or simply admire 
 through wonder or curiosity. We accomplish this simpli- 
 fication of our knowledge by arranging the multitude of 
 diverse things in groups, throughout each of which there 
 runs a certain amount of similarity. There may be many 
 easily-observed points of difference between the different 
 members of one and the same group, and indeed very 
 often the differences are more observable at first sight 
 than the resemblances. But it is the similarity that 
 reigns throughout each group that is to be the guide 
 or key, not only to the single group itself, but also to the 
 position which that group holds in the general system 
 of grouping. 
 
 These similarities, each belonging to one group, must 
 then be placed together, examined, and carefully com- 
 B 
 
2 
 
 CUTTING TOOLS. 
 
 [Chap 1. 
 
 pared ; and this comparison leads to the discovery of 
 underlying principles that are common to all, and which 
 serve to bind the vast mass of diversities all together 
 in one grand whole. This is the simplification that is 
 the aim of science. Science has not yet advanced to 
 such perfection that we should be able at present to 
 include in one simplification all the things we have 
 opportunity of observing and examining, but that is 
 the goal towards which scientific men work, and they 
 will never rest until it has been reached. 
 
 Since these similarities form the lines leading from 
 such complicated ramifications to the most perfect sim- 
 plicity attainable, it is evident that each resemblance 
 that is to regulate a group must be chosen with the 
 greatest care, and only after the most thorough investiga- 
 tion. It must not rest on mere superficial or accidental 
 likeness. It must be a likeness that is the result of 
 
 the most important influence that has guided the growth 
 or manufacture of each object. We must look deep 
 into the nature of the objects, therefore, before we can 
 settle how they are to be arranged. Our method must 
 be rational investigation of the whole character and 
 mode of action of the things examined and classified. 
 Thus, in scientific study, both learner and teacher must 
 exercise to the fullest extent not only their senses of 
 observation, but also their reasoning faculties. 
 
 It is only after long experience in such study that 
 one acquires the power of recognising, among the many 
 comparatively unimportant influences that go to shape 
 things to their final forms, the one or two chiefly 
 important characteristics which reveal their connections 
 with general scientific principles. It is not to be ex- 
 pected, therefore, that the learner can be taught at the 
 outset how to draw out the lines along which the dif- 
 
 ferent groups are to be arranged. The plan of the 
 system of classification must be left in the hands of 
 those advanced students who are slowly, but gradually 
 
 and surely, carrying 
 
 science forward to greater perfection 
 
Chap. I.] 
 
 THE WEDGE. 
 
 3 
 
 by their investigations. In the beginning, the scholar 
 must be content to receive from the teacher an explana- 
 tion of the reasons which guide the formation of each 
 group. These will be supplied in this book by describing 
 as accurately as possible the chief examples in each 
 group, and afterwards drawing attention to the im- 
 portant resemblances reigning throughout each. The 
 student must exercise his reason in recognising these 
 essential similarities ; and after he has thoroughly under- 
 stood the arrangement he will have little difficulty in 
 determining for himself how to investigate and classify 
 any new objects, and, in particular, will be able to deal 
 with the objects with which we are now specially con- 
 cerned, namely Tools. He should not expect from his 
 teacher simply a certain amount of cut-and-dried infor- 
 mation about specific tools. He should expect more 
 than that. He should hope to acquire, from the accu- 
 rate and rational study of a limited number of common 
 representative tools, the power of investigating for him- 
 self any and all kinds of new tools, and even of designing 
 and making new-fashioned tools for new special classes 
 of work that may be required of him. 
 
 3. W edges. — The first group of tools to be considered 
 is that mentioned in paragraph 1, which has been so 
 placed on account of its comparative simplicity. 
 
 The iron or steel wedges used for splitting open logs 
 of timber are so simple and so well-known as to require 
 but little description. They range from two to five inches 
 wide, and in length up to six or seven inches. For 
 harder woods they should have a gentler taper than for 
 softer timber. They ought to be made parallel in width, 
 but for the sake of greater ease in entering they are 
 often made rather narrower at the edge end. This edge 
 is ground to a much more rapid bevel than the general 
 taper of the wedge. The object of this is evidently to 
 obtain a moderately sharp edge without having a long, 
 thin, weak part at the working extremity of the tool. 
 Several wedges are inserted in the line of the split it 
 
4 
 
 CUTTING TOOLS. 
 
 [Chap. I. 
 
 is desired to make, the number used being proportioned 
 to the breadth of the split. They are inserted by blows 
 with a hammer, or, if the wood is too hard to permit 
 this, a shallow saw-drift is sawn across the surface along 
 the line of the intended split, and the wedges inserted 
 in this. They are then driven in by blows from a 
 hammer or axe, care being taken to distribute the blows 
 along the row of wedges, so as not to let any one wedge 
 be driven much farther in than any other at the same 
 time. 
 
 While the rapid bevel of the extreme edge is entering, 
 no splitting of the wood takes place (Fig. 1). The action 
 
 of the tool extends only a very small dis- 
 tance from the surface. A very small por- 
 tion only of the wood is simply crushed. 
 The crushed edges of the timber are, 
 of course, destroyed for all useful pur- 
 poses. The thickness through which it 
 is crushed and destroyed is very con- 
 siderably diminished by cutting, in the 
 first place, the saw-drift mentioned 
 above. The farther the point gets into 
 the wood the wider is the area over which the tool 
 crushes the wood beneath it, and the deeper does the 
 crushing extend, because the material, being supported 
 on either side by the wood beyond, can yield sidewise 
 only to a very limited extent, and must suffer the rest of 
 the crushing that is imposed on it in the direction of 
 depth, It would thus be impossible to continue the 
 large angle of bevel to any great distance from the point 
 of the tool. This large-angled bevel must be very short, 
 and beyond it must begin a much more finely-tapered 
 part. This is the true wedge ; and, as soon as it gets 
 below the surface sufficiently for its sides to bear well 
 against the timber, the splitting commences. 
 
 When the split has just begun, and also after it has 
 extended some little way down the block, the wedge 
 bears against the top edges only of the split surfaces. 
 
Chap. I.] 
 
 WEDGE-ACTION. 
 
 5 
 
 The arrows (Fig. 2) show approximately liow it pushes 
 out the timber on either side. Let us now see what is 
 taking place in the portion of the wood beyond the point 
 to which the split has already extended. The two halves 
 cling together in opposition to the force of the wedge 
 that seeks to separate them. Over the surface that 
 is just about to split open, the left-band half of the 
 wood (marked A in Fig. 2) pulls 
 the right-hand half, B, in the direc- 
 tion shown by the arrow, 2. 
 
 We find, then, the block of 
 wood, b, pushed to the right-hand 
 a force represented by the 
 arrow 1, and pulled to the left- 
 hand by another force lower down, 
 represented by the arrow 2. If 
 these two forces were alone acting , ( , 
 
 on b, it is quite clear that b would 1 1 1 / I M 1 1 
 
 begin to turn round right-handedly, 1 ' i j j 
 
 like the beam of a pair of scales ' j j j | 
 
 which is supported by the knife- ! ^ 1 ll-J, 3 
 
 edge in the centre, and is weighed Fig. 2. 
 
 down by having a weight thrown 
 into one pan without any balancing weight in the 
 other pan. But B, instead of turning round, remains 
 upright while the wedge is being driven in, and it 
 is thus clear that it must be kept in balance by a 
 third force acting on it lower down than the arrow 2, 
 and in the direction shown by the arrow 3. A very 
 little consideration shows that this force 3 can be exerted 
 by nothing but the surface of the half-block A pressing 
 against B in the direction of the arrow 3. While, there- 
 fore, the action of the wedge makes the two halves 
 of the block pull away from each other at about the 
 level of the arrow 2 (or, as it is described in mechanical 
 language, throws the timber into tension in this part of 
 it), it simultaneously causes the lower portions to push 
 against each other — that is, it throws them into compression , 
 
6 
 
 CUTTING TOOLS 
 
 [Cliap. I. 
 
 It is evident that tlie tension is greatest close below 
 the last point at which the two split surfaces have 
 actually separated. From this point downwards the 
 intensity of the tension decreases gradually, until at a 
 certain level it has diminished to nothing. Here the 
 wood is neither in tension nor compression, and beyond 
 this position downwards the compression gradually in- 
 creases from zero to a maximum intensity at some level 
 depending on the length of the block. The compression 
 then diminishes again the farther one goes from the 
 extremity of the split. 
 
 It is clear that the effect of these three forces is to 
 bend the half-block B, the concavity of the bend being 
 to the right-hand side. Fig. 2 shows the top edge 
 only of the split surface bearing against the wedge. 
 Whether this will actually be the case or not in any 
 particular example, evidently will depend on the angle 
 of the wedge, and on the roundness of the curve to which 
 the half-block is bent by the action of the above-mentioned 
 three forces. The block will bend to a sharper curve the 
 softer and more pliable the kind of timber is. The curve 
 will be straight er, on the other hand, the thicker the block 
 is from the line of the split to its outer surface on the 
 right hand. It is found by calculation and by experi- 
 ment that this last-mentioned thickness of material has 
 a much more powerful influence in stiffening the block, 
 and preventing the curve of bending from deviating 
 much from a straight line, than even the hardness or 
 softness of the wood itself has. 
 
 It is easy to see that the distance from the end of 
 the split down to the point at which the tension in the 
 wood (indicated by the arrow 2) has diminished to zero, 
 that is, the length over which the wood is thrown into 
 tension by the action of the wedge, depends altogether 
 upon the curve to which the splitting surface of the half- 
 block is bent. The rounder this curve is the shorter 
 becomes the length of wood thrown into tension, and 
 conversely. How tlie whole pull, indicated by arrow 2, 
 
Chap. I.] 
 
 WEDGE-ACTION, 
 
 /? 
 
 i 
 
 that the half-block A exerts on the half-block b evidently 
 depends upon this length over which tension is dis- 
 tributed, and is, in fact, roughly proportional to this 
 length, because the intensity of the tension per square 
 inch of surface increases gradually from zero at the lower 
 end of this length up to just that amount at its upper 
 end necessary to tear one surface quite away from the 
 other. This last maximum intensity of tension is the 
 same for different blocks of the same kind and quality 
 of timber. It is simply the measure of the direct tensile 
 strength of the wood across its grain. The stiffness of 
 the wood, on which depends the straightness of the curve 
 and the length of the surface over which tension is 
 caused, is measured by what is called the modulus of 
 elasticity. As for the exact ratio in which the pull that 
 the two halves exert on each other in clinging together 
 varies with the above-mentioned elements, an approxi- 
 mate theoretical calculation can be made, and this shows 
 that (other things being equal) this pull is proportional 
 to the fourth root of the modulus of elasticity and to 
 the fourth root of the cube of the product of the tensile 
 strength by the thickness from the split to the outside 
 surface. 
 
 That is, if e = Modulus of elasticity 
 
 T = Tensile strength in the direction trans- 
 verse to the split 
 
 and h = thickness from split to outside surface, 
 then the pull represented by arrow 2 is proportional to 
 
 a/ ET :i /rt 
 
 It varies also, of course, in simple proportion to the 
 width of the split. 
 
 It also decreases a little the greater becomes the 
 length of the split from the bearing points of the wedge 
 down to the last torn part of the newly opened surface, 
 but to explain why it does so would lead to more difficult 
 theoretical reasoning than would be proper here.* 
 
 * The force 1 acts with a moment whose arm increases with the 
 above distance. This moment helps very largely to bend the splitting 
 
8 
 
 CUTTING TOOLS. 
 
 [Chap. I. 
 
 Tins force 2 is balanced by the forces 1 and 3 to- 
 gether. The portion of it balanced by 1 depends on the 
 distance from 2 at which 1 acts, that is, upon the length 
 of the split. The longer this split becomes the smaller 
 does the force 1 become. The same approximate theoreti- 
 cal calculation as is referred to above shows that, 
 roughly speaking, it varies inversely nearly in proportion 
 to the length of the split, and at the same time varies in 
 proportion to 2 Vet P. Taking the last term of this ex- 
 pression separately, it is seen that the transverse force 
 which the wedge exerts on the edge of the wood increases 
 in the ratio of the square root of h ?J or the thickness of 
 the piece split off; that is, it increases in a faster ratio 
 than this thickness but not so fast as its square. # 
 
 4. Wedge-Action in Cutting Tools. — The object of 
 explaining so minutely the action of a wedge in splitting 
 a block of wood will be soon seen, when we find that a 
 most important part of the action of all cutting tools 
 is quite similar to that of the simple wedge. The results 
 of the above investigation will serve to explain many 
 points which are, at first sight, and taken by themselves, 
 difficult to understand, but in the elucidation of which 
 no time need be lost, now that a clear comprehension of 
 the effect of the simplest of all tools has been gained. 
 
 It is to be remembered that the wedge acts in two 
 ways. At first, when the sharp-pointed edge is entering, 
 it causes no splitting, but simply crushes and pushes aside 
 the small quantity of material in close proximity to its 
 edge and into which it penetrates. After it has got a 
 
 fibres, and the curve to which they are bent is sharper the larger is this 
 moment. The sharper the curve in advance of the split, the shorter is 
 the surface exposed to tension. The resulting diminution of the pull 
 2 leads to a corresponding diminution of the thrust 1, but this diminu- 
 tion of 1 is not in quite so great a ratio as the simultaneous lengthen- 
 ing of the arm with which it acts to exert the moment .. 
 
 * If, however, the split be extremely short, the point of the tool 
 following close to the point of actual separation of the material, and 
 the pressure of the tool being exerted close to its edge, then this pres- 
 sure varies more nearly with the f ths power of the thickness of the 
 shaving ; that is, not quite so fast as that thickness. 
 
Cliap. I.] 
 
 9 
 
 MORTISING CHISEL AXE. 
 
 certain distance, it begins to cause a split in advance of 
 its edge, in the manner described in detail above. 
 
 5. Mortising Chisel. — Of the tools named in the first 
 section, that which bears the most resemblance to the 
 simple wedge in the mode of its action is the common mor- 
 tising chisel. It also is driven forward by blows from a 
 hammer, and the thicknesses of the pieces of wood removed 
 by it being large, it acts to a great extent by splitting. 
 Its edge, however, is made much finer and sharper to give 
 more penetrative capacity, in order that it may cut the 
 fresh surface clean and smooth (in a manner that will be 
 presently explained), and because also it is used to cut 
 transversely to the grain of the wood, in which direction 
 the wood both yields to the penetrating edge and also 
 splits with much greater difficulty than in the direction 
 of the fibre. The fine edge is, of course, more liable to 
 be broken by the shocks of the blows than that of the 
 common wedge, and, therefore, a wooden hammer or 
 mallet is used in order to mitigate the violence of the 
 shocks. One other difference is that the one 
 surface of the mortising chisel is made quite 
 fiat, the bevel which makes the extreme edge 
 being put all on one side. This flat surface acts 
 as a guide whereby the tool may be advanced 
 through the wood in a straight line, cutting off 
 all the material lying on one side of that line. 
 
 6. Axe. — The ordinary woodman’s axe (Fig. 3) 
 has no such flat surface on one side. Both sides 
 are rounded off equally, there being no flat bevel 
 on either. The reason of making it so is to allow 
 the workman with greater facility to cut into 
 the wood at any angle he may desire to the 
 surface upon which he is working. The sur- 
 faces being rounded so prevent him from ob- 
 taining accurate flatness in his work, but for 3> 
 his purpose this is of no consequence. The 
 handle, or shaft as it is called, should be of straight 
 grained ash, and is made from 3 to feet long. The 
 
10 
 
 CUTTING TOOLS. 
 
 [Chap. I* 
 
 workman swings the axe round with the full stretch 
 of his arms so as to bring it to the greatest possible 
 velocity at the moment of striking into the timber. 
 As the blade flies backwards past his feet, upwards 
 and forwards overhead, the thick part in which the 
 shaft is fastened runs in advance of the cutting edge dur- 
 ing the earlier moments of this swing, and at some period 
 of the forward stroke the workman brings the cutting 
 edge to the front by giving a gradual twist to the shaft. 
 This twist is given in such a direction as to carry the 
 edge through a semicircle lying away from the workman 
 to his right hand, supposing him to be cutting the right- 
 hand side of the timber. The reason that it swings this 
 way and not round the inner semicircle, is not to avoid 
 any risk of accident, but because in extricating the blade 
 from the timber after the blow, the heavy side of the 
 blade naturally falls outwards to the right hand, and this 
 gives the blade a half turn in the opposite direction to 
 that mentioned above. In order, therefore, that there 
 should not be a continuous rotation of the shaft as the 
 blows succeed each other, which would make it difficult 
 or impossible to keep a firm certain grasp of the shaft, 
 the half turn overhead must take place in the direction 
 mentioned. The blade thus oscillates backwards and for- 
 wards at the bottom and top of its swing without turning 
 continuously in one direction. 
 
 The shaft is made oval, the greatest diameter being 
 in the plane of the blade. The shock of the blow being 
 in this plane, the strength of the shaft to resist breakage 
 requires also to be in the same direction. As great a 
 depth as can be conveniently grasped in the hand is, 
 therefore, given in this plane. By making the transverse 
 thickness smaller this depth can be made greater, because 
 the size that can be firmly grasped in the hand depends 
 more on the length of the circumference than on the 
 diametral size, the fingers accommodating themselves to 
 any desired shape. The oval section also allows the 
 workman to know by the feel in what position he has 
 
Cliap. I] 
 
 AXE — -HATCHET. 
 
 11 
 
 hold of the axe, and so to direct it that the edge may fall 
 on the wood at the desired angle. 
 
 The shaft lies straight in the plane of the blade ; 
 but as seen perpendicularly to this plane, it is very con- 
 siderably bent in such- a direction as to lower the extre- 
 mity when the axe lies in the cut in the wood. The 
 object of this bend is to avoid the awkward and useless 
 raising of the left hand that would be necessary at the 
 moment the blow is struck if the shaft were straight. At 
 this period of the swing the shaft lies, in ordinary work, 
 at only a moderate angle of obliquity from the vertical, 
 and, therefore, its extremity stands high up, and, during 
 the last instant of the stroke, this extremity swings for- 
 ward rapidly. The left hand which grasps this end por- 
 tion avoids the necessity of following this awkward 
 movement, by slipping along the bent portion to the 
 extreme end of the handle. This bend is also probably of 
 use in some degree in steadying the tool as it cuts into 
 the timber, and preventing it heeling over to one side. 
 
 Very little advance has been made for a long time 
 past in England in the design of this felling axe, prob- 
 ably because of the comparatively little work remaining 
 to be done by it in this country, the forests having dis- 
 appeared during the gradual spread of land cultivation 
 for agriculture. In America more modern patterns are 
 used. The blade is of higher-class steel, is more uni- 
 formly tapered in thickness and altogether thinner and 
 lighter, the angle of the cutting edge being acuter and 
 capable of being sharpened more keenly. It is used with a 
 much swifter stroke than the more ponderous old English 
 axe could be driven with, and, the extra lightness more 
 than compensating for the increased speed, more work is 
 done with it, and with less fatigue, than with the heavy pat- 
 tern. These axes are now used to some extent in England. 
 
 o 
 
 7. Hatchet. — The Hatchet is a tool quite similar to 
 the axe for lighter work. It has a short straight shaft, 
 and can be wielded with one hand. What is called a 
 side hatchet lias the thickened head for the reception of 
 
12 
 
 CUTTING TOOLS. 
 
 [Cliap. I. 
 
 the shaft end lying all to one side, so as to leave one side 
 quite flat. No bevel is put on the edge on this side, the 
 bevel being wholly ground from the other side. This is 
 used for flattening the vertical sides of posts, etc., but is 
 not a good tool for the purpose. 
 
 8. Adze. — The Adze has a blade which stands perpen- 
 dicular to the shaft and to the plane in which it is swung. 
 The surface which is cut by it is thus perpendicular to 
 the plane in which it is swung. The blade, as shown in 
 
 Fig. 4, is curved in the direction in 
 which it is swung. The object of this 
 is to allow the front surface of the 
 blade to lie flat down on the surface 
 which is being worked, and thus act as 
 a guide to the advance of the cutting 
 edge ; and at the same time to allow 
 the end of the shaft, which stands a 
 small distance beyond the front surface 
 of the blade, to clear the surface of the 
 timber. It also allows the tool to be 
 heeled over slightly after being driven 
 into the wood, so as to break off the shaving that has 
 been cut. The dotted line in Fig. 4 is a tangent 
 to this front surface of the blade at its cutting edge. 
 This tangent stands a short distance clear of the end of 
 the shaft. As the edge is worn away and re-ground, 
 this tangent will fall gradually nearer the end of the 
 shaft. The sharp end is made by grinding one bevel 
 only, which is on the inside, that is, away from the 
 timber being cut. If the outside is quite straight cross- 
 wise, and regularly curved, this tool is capable of produc- 
 ing very true flat surfaces. It is used both with a long 
 shaft, swung with both hands, and with a short one held 
 in one hand only. 
 
 9. Pen-knife. — The Pen-knife is in every respect 
 similar in form of cutting edge and in action to the axe 
 with a two-bevelled edge, except that it is driven into 
 the material to be cut by a steady pressure, not by a 
 
Chap. I.] 
 
 PARING CHISEL, 
 
 13 
 
 blow. Being rounded on both, sides, it is incapable of 
 producing truly flat surfaces. 
 
 10. Paring Chisel. — The most perfect instrument of 
 the sort now being described for cutting wood is the 
 ordinary paring chisel. These chisels are made from 6 to 
 10 inches long, and from -|th of an inch to 2 inches wide. 
 In order to give sufficient strength, the very narrow 
 ones are made extra thick, as shown in Fig. 5, b. The 
 length is made greater for the larger widths, but in 
 
 a 
 
 Fig. 5. 
 
 consequence of frequent re-grinding and re-sharpening, 
 broad chisels of very short length are as often met with 
 in the workshop as narrow chisels are. 
 
 In the process of manufacture both faces of the 
 chisel are ground. One of these is ground very care- 
 fully flat. The other side is ground to a bevel at the 
 edge, the angle between the bevel and the flat face being 
 about 30°. The wood to be cut is steadied in its position 
 on the bench by the left hand, and the chisel handle 
 is grasped by the right hand. The left shoulder is placed 
 on the top of the chisel handle, and pushes it forward, 
 while the right hand guides and steadies it, the flat face 
 of the blade being always kept towards the workman. 
 
14 
 
 CUTTING TOOLS. 
 
 [Chap. I. 
 
 In sharpening the chisel on the oil-stone, some work- 
 men lay the bevelled surface flat down on the stone, 
 so that the whole surface is rubbed on it, but the 
 more common custom is to rub only a small facet, 
 making, with the flat face, an angle 5° or 10° greater 
 than that of the ground bevel. If the chisel has been 
 ground carefully to a fine edge, the first method may 
 be followed with great advantage at the first setting on 
 the oil-stone, but in subsequent re-settings much time 
 is lost by doing so, because of the large surface to be 
 rubbed down. Whatever be considered the proper 
 angle for the facet, it is easy to grind the bevel to an 
 angle smaller than it by a few degrees, and thereby to 
 secure a small sharpening surface on the facet. The 
 advantage of rubbing down the ground bevel at the first 
 setting seems to consist in providing a smooth surface 
 over which the shavings may slide, whereby less force is 
 required to shove the chisel onward. It costs but little 
 trouble to smooth away the roughnesses of the grinding, 
 because these, instead of constituting a complete un- 
 broken surface, are actually merely projections scattered 
 here and there, the total area of which bears a very 
 small ratio to that of the surface on which they stand. 
 The first edge, prepared in this way, stands undulled a 
 considerably longer time than the subsequent edges with 
 the larger facet-angle do. 
 
 11. Grinding W ood Tools. — In grinding wood tools in 
 general — not only those mentioned in this chapter, but 
 also plane-irons, &c. — it is well to avoid the very common 
 practice of continuing the grinding until a feather-edge 
 is produced. This is a strip across the edge of from 
 one-32nd to three-32nds of an inch wide, which bends over 
 under the pressure of the grindstone when the edge is 
 ground verv thin. This feather-edge has afterwards to 
 be removed by cutting with it across the grain of a piece 
 of wood. Its removal means simply the loss of so much 
 of the length of the chisel unused. After the feather is 
 taken off, the thickness of the edge left is no less 
 
Chap. I.] SHARPENING EDGE TOOLS. 15 
 
 than can easily be obtained by carefully grinding to the 
 limit that is reached before the bending begins to form 
 the feather. Another advantage of avoiding the feather 
 in grinding is that it allows one to see whether the 
 edge has been ground to a uniform thickness through- 
 out its width. This is impossible when a feather is 
 formed. 
 
 12. Setting Edge Tools. — In using the chisel for 
 work that needs to be finely finished, the most common 
 mistake made by beginners is to use it too long before 
 re-setting the edge on the oil-stone. Suppose that half 
 an hour’s work shortens the blade, as measured to the 
 exact cutting edge by T t.„th of an inch. To bring the 
 edge once more to its original keenness requires a certain 
 amount of rubbing on the stone, the amount correspond- 
 ing to g-^pjth of an inch on the flat face. In ten minutes’ 
 work the blade will be shortened by, say, about one-third 
 of -g-igtli or g-jjoth of an inch, and the amount of rubbing 
 to bring back the edge to the original sharpness after 
 this amount of work is not more than one-third of that 
 needed in the first case. Thus, if in the half hour 
 the edge be sharpened thrice instead of once, the total 
 amount of rubbing required will be no greater than that 
 needed at the end of the half-hour if no sharpening has 
 been performed since the beginning of it ; while, in the 
 former case, the edge will at no time have become more 
 than one- third as blunt (i.e., the edge no more than 
 one-third as thick) as it is at the end of the half- 
 hour in the latter case. Thus, by having the oil-stone 
 always at hand, clean, and in good condition, and by 
 having very frequent recourse to it to keep the chisel 
 edge constantly sharp, a great deal of unnecessary labour 
 is saved, and the work is done more nicely. Of course, 
 this rule cannot be followed unless the oil-stone is 
 always ready to be used ; otherwise, much time would be 
 lost in getting it ready so often. This rule also cannot 
 be adopted to so great an extent with, for instance, 
 plane-irons, with which a considerable amount of time is 
 
16 
 
 CUTTING TOOLS. 
 
 [Chap. I. 
 
 lost in taking the tool to pieces and putting it together 
 again every time the edge is set. 
 
 13. Paring Action. — The special characteristic of all 
 the tools that have hitherto been mentioned is, that each 
 lias a blade which follows the cut made by the edge into 
 the wood, so as to keep the plane of the blade coincident 
 with that of the cut. In consequence of this feature, the 
 material removed by the tool does not need to be thrown 
 off in short lengths,’ in order to leave the way clear 
 for the advance of the tool. It sometimes gets broken 
 in short lengths, as, for example, in cutting across the 
 grain, but this is not necessary for the passage of the 
 tool, and only results from the excess of brittleness 
 of the material in certain directions. The tool passes 
 between the wrought surface and the material removed, 
 and simply bends this latter aside to a greater or smaller 
 extent. The bending is, in some cases, large enough 
 to crack it in irregularly long pieces, but it is not neces- 
 sarily broken into separate bits. 
 
 The first function of the blade is to act as a support 
 to the penetrating edge, which is pushed forward by 
 it. Its second function is to bend aside the material 
 sufficiently to open a passage for itself. It must be 
 strong enough to perform these two functions simul- 
 taneously wdthout risk of being bent or broken. It has 
 a third function — namely, that of guiding the advance of 
 the penetrating edge more or less nearly in one and the 
 same plane. 
 
 The function of the sharp edge is to penetrate the 
 material at the desired place and in the desired direction, 
 and it does this simply by crushing a minute quantity of 
 material in front and on either side of it, and pushing it 
 to one side and the other, somewhat in the manner in 
 which water is thrust to one side by a solid body entering 
 it. Its work is facilitated by a transverse tensile strain 
 being put on the material in front of it by the bending 
 action of the blade, and this is more especially the case 
 when the cut is nearly parallel to the grain of the wood. 
 
Chap. I.] 
 
 PAT1ING ACTION. 
 
 17 
 
 Let Fig. G represent on an exaggerated scale tlie 
 blade of a paring chisel taking a thick shaving (the 
 thickness of which is exaggerated, proportionally, more 
 than is the rest of the sketch) off a flat surface. Let the 
 small arrows represent the splitting force which the blade 
 exercises against the shaving, and conceive the thick- 
 ness of the shaving to be divided into three layers, by 
 the dotted lines. We have seen that the splitting force 
 
 Fig. 6. 
 
 required to tear up a layer increases faster than in the 
 simple ratio of the thickness of the layer. Therefore, 
 the force required to tear up the topmost of the three 
 equal layers from the middle one, is somewhat less than 
 one-third of that required to tear up the whole shaving 
 of triple thickness, if this shaving hold together in one 
 piece. But the pressure exerted by the tool blade on 
 the under surface of the shaving is — a large part of it, at 
 any rate — transmitted through the thickness of the 
 shaving to the upper layers. The whole of it is not so 
 transmitted ; part is balanced by the resistance to bend- 
 ing that the undermost layer independently offers, and a 
 second part is in the same way balanced by the second 
 layer. But more than two-thirds of it is transmitted to 
 the second layer, and probably more than one-third is 
 passed on to the third layer. The force, then, that bears 
 against the under-surface of the second layer is more than 
 sufficient to tear up the two topmost layers taken 
 together from the undermost layer ; and again that which 
 reaches the top layer is probably more than sufficient to 
 c 
 
18 
 
 CUTTING TOOLS 
 
 rChnp. I. 
 
 tear it up from the middle one. Thus a thick shaving 
 gets split up into a number of different layers of various 
 thicknesses, according to the small differences of cohesive 
 strength between the different fibres. As every one who 
 has used the chisel knows, these splits run often a con- 
 siderable distance in advance of the tool. They are not 
 always decided splits. But if the shaving be examined 
 carefully when the tool is pressing on it (if necessary 
 with a magnifying glass), it will be found that even when 
 the layers are not actually pulled apart, they are on the 
 point of separating, the delicate fibres being pulled out 
 into a loose tangle. Thus the undermost layer is left 
 very thin and pliable, and is easily dealt with by the 
 sharp cutting edge. 
 
 If the material be not very coherent transversely to 
 the fibre, this undermost layer lies closely down on the 
 
 facet of the edge, and no trace of a decided split, how- 
 ever short, can be found immediately in front of the 
 edge. If, cfti the other hand, the fibres cohere more 
 strongly together, a small opening is found extending a 
 short distance in front. How this split, of course, follows 
 the grain of the wood, which is not necessarily the 
 desired direction of the cut. The sharpened edge has, 
 therefore, still to perform its cutting function. It is 
 guided by the flat face of the blade which is pressed 
 against the already cut surface of the wood, and it cuts off 
 and raises from the forward extension of that surface all the 
 wood left by the small split above that same surface. It 
 
0 hap. LI 
 
 19 
 
 PARING FORCE. 
 
 is in this case continually beginning new small shavings, 
 just the first minute length of which is separated from 
 the larger shaving above. The free ends of these new 
 layers are so short that they are not perceived without 
 very close inspection. As soon as the new layer is 
 fairly started as a shaving, the little advance-split changes 
 place, and runs underneath the new layer of the shaving. 
 
 Fig. 7 will give some idea of this action of the cutting 
 edge, but it would require a still larger scale of exagge- 
 ration to show it clearlv and exactly. 
 
 aJ *■' 
 
 14. Power required to Pare Wood— The power re- 
 quired to drive forward a tool of this description depends 
 (a) on the quality of the material ; ( b ) on the direction of 
 the cut relatively to the grain ; ( c ) on the thickness of the 
 shaving ; (d) on the angle of the tool bevel ; and (e) on 
 the keenness, or perfection of fineness, of the cutting edge. 
 
 Experiments made by the author with a chisel 1| 
 inch broad gave the following results for yellow pine and 
 mahogany. 
 
 1st. Yellow pine plank, well seasoned and straight 
 grained, If inch thick. The chisel-cut taken was the 
 whole thickness of the plank. 
 
 (a). Cut parallel to the grain. Chisel 1J inch wide 
 by -V" thick ; yk" length of bevel ; -fy" length of small 
 facet forming cutting edge. 
 
 Thickness of Shaving. 
 
 0-01 
 
 0-03 
 
 0-1 
 
 0-18 
 
 inches 
 
 5 J 
 f) 
 
 V 
 
 Force required to drive 
 Chisel forward. 
 
 14 
 
 21 
 
 35 
 
 41 
 
 lbs. 
 
 V 
 
 >) 
 
 )) 
 
 (i b ). Cut at 45° to the grain. Chisel wide by 
 g y ' thick j length of bevel ; length of small facet. 
 
 Thickness of Shaving, 
 
 0-02 inches . 
 0-03 
 
 Force required to drive 
 Chisel forwnrd. 
 
 28 lbs. 
 
 37 , , 
 
20 
 
 CUTTING TOOLS. 
 
 ICliap. I. 
 
 (i c ). Cut perpendicular to the grain. Same chisel as 
 in (b). 
 
 Thickness of Shaving'. 
 
 Force required to drive 
 Chisel forward. 
 
 0'025 inches . . . . . .45 lbs. 
 
 0-08 „ 90 „ 
 
 2nd. Mahogany of common cheap quality, quite 
 
 dry. 
 
 The same chisel was used as in (b). It was found 
 impossible to measure satisfactorily the force required to 
 cut parallel to the grain, because of the irregularity of 
 the splitting. 
 
 Cur at 45° to the grain. 
 
 Shaving 0‘02 inch thick. Force required 57 lbs. 
 
 Cut perpendicular to the grain. 
 
 Shaving 0*01 inch thick. Force required 61 lbs. 
 
 Examining the numbers for yellow pine, cut parallel 
 to the grain, it is seen that the force does not increase 
 nearly so fast as the thickness of the shaving. It was 
 shown that the part of the force which is spent in 
 splitting the material increased faster than this thickness. 
 The above result shows, then, that most of the force 
 in this case is spent not in splitting, but in the pene- 
 tration of the cutting edge, the power to drive which 
 forward into the wood, as previously described, increases 
 only slowly (if at all) with the thickness. To this latter 
 there is also to be added the friction between the chisel 
 face and bevel and the cut surfaces. 
 
 The same may be said of the forces found by ex- 
 periment necessary for cutting at 45° and 90° to the 
 grain. Here one part of the power exerted is spent 
 in shoving the thin segments, into which it is easily 
 observed that the shaving is half-broken transversely, 
 one over the other perpendicularly to the line of the cut ; 
 and this amount of power varies nearly in proportion to 
 the thickness, but it forms only a small portion of the 
 whole power used. 
 
 15. Tools for Metal. — Ho tools similar to those that 
 
ciiap. ii.] clipping chisels. 21 
 
 have now been described are used for tlie harder metals. 
 Lead, tin, and solder can be cut with a knife or paring 
 chisel, the action being very similar to that of the same 
 tools used on wood. 
 
 CHAPTER IL 
 
 CHIPPING CHISELS AND HAND PLANES. 
 
 1. Difference from Tools of Chap. I. — The tools with 
 which the last chapter dealt have all this peculiarity, 
 that the face of the blade lies close down oil the surface 
 tliat is cut, and that the tool has no other guide than 
 the contact of the blade-face with this surface. There 
 is a numerous class of cutting tools which differ from 
 these chiefly and almost solely in having a small angle 
 between the under surface of cutting edge and face of 
 the work. 
 
 2 . General Characteristics. — These have sometimes 
 two bevels, one on each side, and sometimes a single 
 bevel on one side only. 
 
 Most of these require to be guided mechanically, 
 so as to cut in a straight line ; but at least one — namely, 
 the cold chisel for iron, steel, or brass, is used without 
 any such guide. 
 
 8. Cold Chisel. — The cutting angle of the cold chisel 
 is smaller than that of other tools for iron, it being ground 
 to from 40° to 70° according to the quality of metal 
 to be chipped. Apparently the sole reason for this is 
 that, it being a hand tool, the power available for driving 
 it forward is strictly limited. The power required is 
 lessened by making the edge keener, but at the same 
 time durability of the edge is to a large extent sacrificed. 
 This is readily recognised by comparing the lengths 
 of cut that can be accomplished by a chipping chisel and 
 
22 
 
 CUTTING TOOLS. 
 
 [Chap. II. 
 
 a planing-machine tool before each needs re-grinding. 
 It is doubtful, therefore, whether the angle of the 
 chipping chisel would be the best if the workman’s hand- 
 power were unlimited. It is to be remembered, however, 
 that the interruption to the work of the fitter, caused by 
 his having to re-grind his chisel, is not of nearly so much 
 importance as the stoppage of a planing-machine, yor 
 other power-tool, for the re-setting of the tool-edge. In 
 the one case, only the man’s time is lost ; in the other, 
 the machine as well as the man is for a certain time 
 prevented from doing productive work ; and this is 
 equally true whether the machine is left standing while 
 the man goes and re-dresses his tool, or whether it is 
 stopped only long enough to change the tool, the re- 
 dressing of the tool being handed over to another work- 
 man whose special duty it is to re-grind and make 
 all the tools of the shop as wanted. Probably if 
 no expensive loss of time occurred in changing tools 
 very frequently, it might be found more economical to 
 use keener edges for lathe and planing-machine tools 
 than are used at present. It seems certain that a less 
 amount of power would be needed to perform the cutting 
 with such tools, provided they were kept keen. 
 
 There is, however, a certain cutting angle for each 
 quality of metal below which it is impossible to use 
 a chipping chisel. The edge will be either broken or 
 completely blunted with only one or two blows if it 
 be ground too keen, and this, too, without these one 
 or two blows accomplishing any appreciable amount of 
 work. Thus, in order to ensure its edge lasting a useful 
 length of time, the fitter has to grind his chisel in 
 accordance with the quality of the metal he has to 
 work, the proper angle being greater for the harder and 
 tougher sorts. 
 
 4. Chipping Hammer. — Chipping hammers vary in 
 weight from to 2 lbs. The best weight is If or ljlb., 
 according to the size and strength of the workman. A 
 workman can more usefully employ his strength — that is, 
 
Oliap. II. J 
 
 GUIDANCE OF CHIPPING CHISELS. 
 
 23 
 
 he can get more work done with a given expenditure of 
 time and strength — by hitting hard and swiftly with a 
 light hammer than by hitting sluggishly with a heavy 
 one. The difference is here analogous to that previously 
 mentioned between the light American axes and the 
 old-fashioned heavv English ones. The arm shoulc 
 be swung from the elbow, not from the shoulder. The 
 latter swing would exhaust the body more, and would 
 give a less steadily guided motion to the hammer. The 
 edge of the chisel should be kept moist, either by wetting 
 it in the mouth or by dabbing it on a piece of waste 
 soaked in oil. 
 
 5. Guidance of Chipping’ Chisels. — The angle at 
 which the chisel must be held to the worked surface 
 in order that it may run neither in nor out but con- 
 tinue cutting a shaving of ecpial thickness depends on 
 the toughness of the material, on the keenness of the 
 chisel-edge, and on the thickness of the shaving. A 
 thick, stiff shaving presses the chisel-edge downwards 
 into the material with great force. The chisel must 
 be held closer down to the surface ; the tougher the, 
 material, the smaller the cutting angle of the chisel, 
 and the thicker the shaving. It would be futile to 
 attempt to express mathematically the dependence of the 
 right angle upon these different quantities. Even with 
 prolonged experience, one can only make a very roughly - 
 approximate estimate at starting. The proper angle 
 is always found out as the work proceeds by feel, and 
 by watching how the chips come off. After two or three 
 blows, a good fitter sees what the right angle is, and 
 practice gives him the power of keeping so exactly to 
 this correct angle that he can produce a fairly smooth 
 and accurately flat surface with the chipping chisel alone. 
 When he comes to a place where thicker chips have to be 
 taken off, because of unevenness of the outside “ black ” 
 surface, he instinctively alters slightly the inclination 
 of his tool, so as to prevent the stiffer shaving driving it 
 below the level of the surface he wishes to produce. 
 
24 
 
 CUTTING TOOLS. 
 
 [Chap II. 
 
 This keeping exactly to a level surface in chipping is 
 perhaps the most curiously delicate operation in the whole 
 range of tool-cutting. It is the result of the balance 
 between the downward component of the force of the blow, 
 of the resistance of the material to the advance of the 
 penetrating edge which may be taken as directed along 
 the centre-line of the chisel, and of the oblique down- 
 ward pressure of the shaving (which resists being bent 
 upwards) upon the higher portion of the upper bevel 
 of the chisel-edge. The mathematical expression of this 
 balance would be an equation of great complexity. 
 
 6. Penetration by Chisel Edge. — The character of the 
 penetration of the extreme edge into the metal differs 
 from that of the wood chisel into the wood (as explained 
 in the last chapter) only because metal partakes more 
 of the characteristics of a fluid than does wood. Under 
 great pressure almost any metal, if not hardened by fire 
 or by chemical admixture with noil-metallic substances, 
 can be made to flow or ooze from one shape to another 
 like a viscous fluid, such as treacle or soft mud. As the 
 chisel-edge is thrust forward, it to a certain extent com- 
 presses the metal immediately in front of it, but probably 
 the material makes way for its passage chiefly by this 
 flowing movement, and the greater part of the resist- 
 ance it offers to its advance is a viscous resistance. This 
 fluidity of the material accounts for there never being 
 any splitting in advance of the tool-edge, as there is in 
 wood. Such splitting hardly ever occurs in chipping, 
 even with bad laminous iron. 
 
 7. Wood Hand Planes. — Wood Hand Planes have, 
 like the chipping chisel, a thin blade, the under surface 
 of which is held up at a certain small angle from the 
 surface being worked. This angle varies from 10° to 
 25° in planes intended for the commoner softer timbers 
 and for the harder and more cross-grained sorts. The 
 upper face of the blade is ground flat, there being a bevel 
 
 and small facet on the under side only. This bevel is 
 
 %* 
 
 ground at an angle of from 20° to 25° to the upper face 
 
Clmp. II] 
 
 II A XI PLANES. 
 
 25 
 
 • — that is, the length of the bevel h from three to a little 
 less than tAvo and a half times the thickness of the blade. 
 The small facet may have an angle from 15° to 10° greater 
 than this, so that the upper face lies at from 45° to 60° from 
 the surface of the work. 
 
 Tn all the planes used by joiners, except some few for 
 special work, such as moulding, the “ plane iron,” or 
 
 blade, is stiffened by having a second “top iron ” screwed 
 down on its flat surface. This bears against the flat face 
 only at its two, ends, and, being itself thin, presses against 
 the edge with a yielding springy force ; the spring, how- 
 ever, being a very stiff one. The edge of the top iron is 
 placed close to the cutting edge — the closer the finer the 
 shavings are desired to be — -and this springy pressure it 
 exerts prevents, or very greatly deadens, “ chattering,” 
 that is, unsteady bending before the always- varying 
 resistance of the material cut. This bending can take 
 place only betAveen the cutting edge and the top of the 
 
26 
 
 CUTTING TOOLS. 
 
 [Chap. II. 
 
 bevel, at which latter point the iron is supported by 
 resting on the “ stock. 7 ’ Above this point also it is 
 held firmly by the wedge, which is driven in to fasten 
 it in its place in the stock (see Fig. 8). The top-iron 
 also serves another purpose, which will be explained 
 farther on. 
 
 The stocks of the longer planes are made of wood. 
 Those of the shorter planes are also most usually made 
 of wood, but iron stocks are becoming common for them 
 in America, and to some extent are already used in 
 England. The edge of the slit in the sole of the wooden 
 stock wears away with the passage of the shavings past 
 it, and after a time leaves this slit too wide. This is 
 rectified usually by letting in a small flat plate of hard 
 wood screwed down to the sole. A brass plate is 
 occasionally inserted, and of course this wears much 
 longer ; but it is not advisable, because of the difficulty 
 in getting the surface of the brass exactly co-planar with 
 that of the wood part of the sole. When the sole needs 
 to be re-stripped, the brass must be removed, the wood 
 stripped, then the brass re-screwed in place and filed 
 down level with the fresh surface of the wood. A 
 still more important disadvantage, however, under 
 which wooden stocks labour in comparison with iron 
 ones, is that the wooden sole gradually loses the per- 
 fect flatness of its surface from the warping of the 
 wood, from unequal wear in different parts, and from 
 “ scoring, ” i.e., being grooved by being accidentally driven 
 over nail-ends. The iron surface having been made 
 once true, remains so always. 
 
 The Jack Plane, Fig. 8, for rough, heavy work, has a 
 stock of about 14 inches in length. The iron is ground 
 with a slightly-rounded contour, so that the plane really 
 ploughs out broad, rounded furrows. The top iron is 
 set back from the edge about -rV inch. 
 
 The Trying or Half -Long Plane is 20 to 22 inches long, 
 and the Long Plane about 26 inches. These have the 
 edge ground straight across, rounded off only a little at 
 
Chap. II.] 
 
 GUIDANCE OF PLANES. 
 
 27 
 
 the corners, and the top iron should not be more than 
 about back from the cutting edge. 
 
 The Smoothing, or as it is sometimes called, Hand 
 Plane, is made of various lengths up to 8 inches long 
 and is used on as many different classes of work. 
 
 There are also various small planes for hollow work. 
 An extremely useful form of iron-stock plane is shown in 
 
 Fig. 9. It has a flexible sole-plate, which can be screwed 
 up to any radius of curvature. 
 
 8. Guidance of Planes. — We have here quite a 
 peculiar sort of guidance for the cutting motion of the 
 tool. Consider a trying-plane in the middle of its stroke, 
 both the front and hind ends of the stock lying on the 
 plank, that is, neither overhanging the end of the plank. 
 
 Behind the tool the surface has been cut down by the 
 thickness of a shaving. In front of the edge of the iron 
 it remains still uncut, and, therefore, higher than the 
 hinder portion. The flat sole is, therefore, tilted 
 slightly upwards, the forward end being the higher. If 
 the wood were perfectly hard and incompressible, 
 evidently the sole of the plane would rest on it im- 
 mediately in front of the iron, and also at the hinder 
 end of the stock, the front end of the sole being raised 
 out of contact with the wood. The cutting edge would 
 then be below the uncut suilace in front of it by a depth 
 equal to the distance it projects below the sole-plate, and 
 
28 
 
 CUTTING TOOLS. 
 
 [Chap. II. 
 
 if this were also the height of the uncut surface above 
 the cut surface where the tail-end of the sole rests, 
 evidently the relative positions of the different parts 
 would be maintained constantly the same as the plane 
 moves forward. 
 
 But the wood is not incompressible, and the workman, 
 bearing heavily on the fore-end of the stock, causes the 
 
 front half of the 
 
 hinder end also at the same time rests upon it, it is clear 
 that the portion immediately in front of the iron must 
 be slightly pressed below its natural position, and the 
 cutting edge of the iron also must be a little below the 
 position we first supposed it to have, that is, it lies at a 
 somewhat greater depth below the surface of the wood 
 
 rig-. 11 
 
 at the front end of the stock, than does the wood surface 
 at the hinder end of the stock. Both on this account, 
 and on account of the compression of the material 
 immediately in front of the iron (whereby a given thick- 
 
Cliiip. II.] 
 
 GUIDANCE OF PLANES. 
 
 29 
 
 ness of shaving means a greater quantity of material), it 
 is clear that there is a tendency for the cut to get a little 
 deeper as the stroke advances. Of course, there is a 
 a limit to this deepening. Either the front or the 
 hinder end of the sole soon stands a minute distance 
 clear of the wood surface, # and the depth of shaving 
 cut is simply that of the projection of the edge of the 
 iron below the sole, increased slightly in proportion to 
 the pressure exerted by the workman. The real bearing 
 is evidently over the surface, extending only a small 
 distance in front of the iron. 
 
 It may be asked, then, what is the advantage of 
 having a long sole for trueing up. The answer is, of 
 course, that in the above explanation the uncut surface 
 was assumed to be already truly flat, and it showed that 
 so long as an equal pressure downwards was exerted, the 
 planing would not bring the surface out of truth. But 
 if there be unevennesses, however minute, that is, even 
 if their height be only a fraction of that of the cutting 
 edge beyond the sole-plate, then when the tool is over the 
 hollow parts the whole or the greater part of the pressure 
 is borne at the ends of . the sole, while the iron either does 
 not cut at all, or removes only an extra thin shaving; 
 when, however, it is over a high place, the full pressure 
 comes on the part of the sole near the iron, and this latter 
 takes its full cut, thereby reducing the unevenness. 
 
 It is evident also that, if he choose, the workman can 
 plane a hollow by pressing first lightly, then heavily, and 
 again lightly, until he lifts the plane entirely off the plank. 
 In this way, he can reduce any high portions he discovers 
 by the application of a straight-edge. 
 
 The pressure put on the material immediately in 
 front of the iron greatly conduces to the clean cutting of 
 the surface. It prevents splitting and tearing of the 
 wood in advance of the tool. 
 
 * Chiefly the hinder end, because the iron does not cut a trach the 
 full width of the sole-plate, which therefore cannot descend to the 
 bottom of this track without being heavily pressed. 
 
30 
 
 CUTTING TOOLS. 
 
 [Chap. IT. 
 
 There is always a tendency to “plane round.” i.e ., to 
 make the ends of the board lower than the centre. This 
 is because at either end of the stroke one of the ends of 
 the sole is free of the wood, and therefore the iron always 
 takes its full cut. In the middle of the stroke it takes 
 its full cut only at the high places. To counteract this 
 tendency, no downward pressure should be put on the 
 stock at the beginning and end of the stroke. 
 
 9. Difference between Wood Plane and Paring 
 Chisel. — The chief difference between the mode of cutting 
 of the plane iron and that of the paring chisel previously 
 explained in detail has already been pointed out, namely, 
 that the wood in front of it is kept firmly pressed down 
 so that it cannot split far in advance of the edge. This 
 splitting is further prevented by the shaving being 
 broken or rather half broken through as soon as it 
 leaves the surface. In examining a shaving from a 
 plane, lines or small ridges are seen running parallel 
 and crosswise, close to each other. If the plane is in good 
 condition and the wood be of even texture, these ridges 
 are spaced the one from the other at very regular dis- 
 tances. These are the above mentioned lines of half- 
 breakage. If the shaving be bent over, it always cracks 
 along one of these lines. They are seen more easily on 
 thick shavings than on thin, and are farther apart on the 
 thick ones. 
 
 This cracking of the shaving is effected when the 
 shaving slides up the edge of the top iron. Holtzapffel 
 seemed to think that this was the chief and indeed the 
 only function of the top iron. This idea cannot be taken 
 as being by any means correct. It was probably occa- 
 sioned by the fact that the top iron of the trying plane 
 is placed much closer down on the cutting edge than that 
 of the jack plane, while at the same time the lines of 
 cracking in the shavings from the trying plane are much 
 closer than on those from the jack. But this will be 
 found to result from the greater thinness of the shavings 
 and from the narrower mouth of the former. To test 
 
Chap II.] 
 
 FUNCTION OF TIIE TOP IKON. 
 
 31 
 
 this point, the author closely examined the shavings from 
 a jack and from a trying plane, the mouths of both of 
 which were narrow (the planes being nearly new) and 
 exactly equal. The top iron of the trying plane was put 
 close down to the cutting edge, while that of the jack 
 was set back nearly an eighth of an inch. When both 
 planes took exactly the same thickness of shaving from 
 the same piece of wood, no difference of any kind could 
 he discovered between the shavings from the two, even 
 when examined with the aid of a powerful Codington 
 lens. The cracks were exactly the same distance apart 
 in both. When either plane was set to take a slightly 
 thicker cut than the other, the difference immediately 
 showed in the spacing of the cracks, this being greater 
 the thicker the shaving whether this came from the jack 
 or the trying plane. 
 
 This proves that the chief object in putting the top 
 iron close down to the cutting edge in the trying plane is 
 to keep this edge perfectly steady, so that it may not yield 
 more or less according to whether it cuts over a high or a 
 hollow place. The main object is not the more immediate 
 breaking of the shaving. 
 
 When an old jack plane with the sole worn so that 
 the mouth was wide in front of the cutting edge, wa& 
 used in these experiments, and when very thick shavings 
 were taken, the spacing between the lines of breakage 
 agreed more with the distance of the top iron edge back 
 from the cutting edge than with the width of the open 
 mouth. 
 
 When there is a wide mouth to the plane, the setting 
 back of the top iron conduces to splitting in front of the 
 tool, and in the jack it is set back with this avowed in- 
 tention because, as has been previously explained, split- 
 ting is by far the easiest mode of removing the surface of 
 the wood. 
 
32 
 
 CUTTING TOOLS. 
 
 [Cliap. III. 
 
 CHAPTER III. 
 
 MACHINE PLANES FOR WOOD. 
 
 1. Velocity of Cutting. — The speed with which hand- 
 planes cut wood is necessarily very limited, a great velo- 
 city not being possible to the arm of a man simultaneously 
 with the exertion of considerable power, or even without 
 such exertion. A cutting edge, set as it is in such a plane, 
 could not cut off the shavings cleanly and smoothly at this 
 low velocity, if the sole of the stock did not forcibly com- 
 press the material just in advance of the cut. 
 
 But if the velocity of cutting be very greatly increased, 
 the necessity for applying this holding down pressure 
 close to the tool edge disappears, because the advance of 
 the tool may be made swifter than the speed at which 
 splitting can possibly take place. This is what is done in 
 wood-planing machines driven by steam or water power. 
 
 In these, plane irons precisely similar to those used 
 in hand planes, except that they are without any top iron, 
 are held by screws in grooves cut in a block which re- 
 volves at such a speed as to make the cutting velocity of 
 the tool-edges from 4,000 to 6,000 feet per minute, the 
 slower speed being suited to the harder qualities of 
 timber. 
 
 2. Classes of Machine Planes. — The revolving 
 spindle on which the cutter block is fastened is, in 
 one class of machine, placed horizontally and in 
 another vertically. In all these machines the surface 
 of the wood to be operated on is placed horizontally ; 
 or, where different surfaces at right angles to each other 
 are to be worked simultaneously, the largest and most 
 important of them is horizontal. When the spindle is 
 vertical, therefore, the cutter-block takes the form of a 
 
C'liap. III.] WOOD PLAXINO MACHINES. 33 
 
 disc whose face is parallel to that of the wood to be cut. 
 This class of machine is very little used at the present 
 day, but for heavy work which does not require fine 
 finishing it is very effective in rapid cutting. In suitable 
 recesses in this disc are placed the cutting tools, their 
 cutting edges being horizontal and lying along radii of 
 the disc. They are set and held in place by screws, and 
 to furnish room for these set screws the whole disc is 
 made hollow, a cover-plate being placed over it to prevent 
 the screw-heads and other projecting parts catching the 
 dress or limbs of the workman. A machine of this sort 
 is illustrated in Fig. 12. The face of the disc stands 
 clear, of course, of the wood, because at this high velocity 
 the friction between the two, if they touched, would not 
 only necessitate the loss of an enormous amount of power, 
 but would also generate so much heat as to burn the wood 
 and cause the bearings of the spindle to run dry of oil, 
 and thus get destroyed. 
 
 3. Vertical Spindle Machine. — The bevel of the tools 
 in this and the other machine is somewhat shorter than 
 that of the iron of the hand plane ; that is, the cutting 
 angle is made larger to give the edge greater strength 
 against the occasional sudden extra resistance caused by 
 unevenness of the uncut surface or by knots. The angle 
 at which the blade is set to the plane of the work is also 
 made greater, namely, about 55° or 60°. 
 
 The bearings of the vertical spindle are fixed in the 
 frame of the machine, and do not move. The timber 
 to be cut is passed underneath the revolving disc upon a 
 table, to which it is clamped and which is forced forwards 
 by mechanism. This mechanism usually consists in a 
 toothed rack screwed on the under-side of the table, 
 into which gears a wheel on a horizontal shaft driven by 
 a pinion on another parallel shaft. Both shafts lie 
 underneath the table, and on the latter are placed a fixed 
 and two loose pulleys, round which run, side by side, two 
 belts from the counter-shaft of the machine. One of 
 these belts is “open,” and the other “crossed.” By 
 D 
 
12. — Wood Planing Machine (old pattekn) by Ransome and Co. 
 
Clin.p. III.] 
 
 CUTTING SPEED AND FEED. 
 
 35 
 
 means of a lever and a double fork the positions of these 
 belts can be shifted, so that either of them can be 
 made to run on the fixed pulley, while the other runs 
 on a loose pulley. According as the open or crossed 
 belt runs on the fixed pulley, the table is driven forwards 
 or backwards. 
 
 4. Calculation of Feed. — If the cutters are arranged 
 on a circle of 2 feet diameter, the speed of the spindle 
 should be about 1,000 revolutions per minute, so as 
 to give a cutting velocity of between 6,000 and 7,000 
 feet per minute. If the timber is fed up at the rate of 
 20 feet per minute, the front boundary-line of the cut 
 surface will advance y^o— iw f°°f = 0'24 inch, or about 
 
 each revolution of the disc. If there be just two tools 
 on opposite sides of the circle, each will take a cut of only 
 ~ inch wide ; and if there be four tools, the width of cut 
 of each will be just inch. The actual rate of feed with 
 such machines is often considerably below '20 feet, and is 
 never more than 40 feet per minute, and it is, therefore, 
 apparent that a broad cutting edge is not necessary, and 
 that all the work is done by the corner of the planing- 
 iron farthest from the centre of the disc. Thus, with 20 
 feet of feed and four tools on the disc all the work would 
 be done by the outer ~~ inch of the breadth of the chisels, 
 and if these chisels were 1 inch wide, it is evident 
 that each spot on the planed surface is swept over by 
 the cutting edges 16 times during the passage of the 
 front side of the disc, and again 16 times while the back 
 side of the disc passes forward over this part. The first 
 16 sweeps take place, say from left to right, and the 
 second 16 sweeps are in the reverse direction. The 
 surface is therefore very thoroughly worked over, and 
 if it is not left quite smooth and flat, the fault will 
 be in the bad and irregular setting of the chisels, or 
 in the unsteady, trembling revolution of the spindle 
 and its disc. The disc, being a somewhat heavy casting, 
 must be very carefully turned, so that it may be perfectly 
 balanced in order to avoid unsteadiness in its motion ; 
 
36 CUTTING TOOLS. [Chap. III. 
 
 and also with the same object the upright bearings must 
 be made particularly long (so as to wear well), and the 
 brackets in which they are inserted particularly strong 
 and stiff. 
 
 5. Importance of Correct Setting of Chisels.— If 
 
 one chisel is set a little lower than the others, or if 
 it is set so as to have its outer corner not quite so 
 far from the disc-centre, it is clear that it will do 
 little or no work. Therefore, very exact setting of the 
 chisels is absolutely essential in order to make the 
 machine work up to its proper capacity. It is also clear 
 that, if the timber be not fed along a line which is 
 exactly perpendicular to the axis of the revolving spindle, 
 the disc- cutters will reach farther towards the wood 
 either on the front half of their revolution than on 
 the back half, or vice versa. If this line is the slightest 
 degree inclined one way, the cutters will rise quite 
 clear of the planed surface on the back half of their 
 circular path, and a valuable series of finishing grazing 
 cuts will be quite lost. If it is in the least inclined 
 the other way, the cutters at each passage through the 
 hinder part of their revolution will leave a scar or 
 scratch. These scratches will be distant from each other 
 by the amount of feed per revolution of the disc— for 
 example, ■— inch in the case taken above. It is, there- 
 fore, of very great importance that the spindle should be 
 set with perfect exactitude perpendicular to the slides on 
 the bed along which the table travels. To attain this 
 accuracy, the only practicable method is to provide means 
 of adjusting the bearings of the spindle after the machine 
 is bolted down to the foundation, and to keep them in 
 adjustment after they begin to wear. Such means are not 
 difficult to provide, but this point has not been hitherto 
 attended to in the design of these machines. Probably 
 on account of this difficulty in setting, and the unsteadi- 
 ness inseparable from long standard brackets subjected to 
 the variable side-thrust mentioned hereafter, this machine 
 has now cone much out of fashion. 
 
Clap. III.] MODE 0F CUTT1NO. 37 
 
 6. The Cut on Vertical Cylindrical Surface. — In 
 
 each new cut the material has not only to be removed 
 from the horizontal surface which is planed, it has also 
 to be separated from the farther advanced portions of 
 timber to which the tool does not yet reach. This 
 separation takes place over a vertical cylindrical surface. 
 If the tools used are only chisels with horizontal cutting 
 edges, this separation is left to be done by tearing simply. 
 Now this would be wasteful of power, and, besides, would 
 introduce danger, and at times certainty, of leaving- 
 ragged torn holes and marks underneath the tooled 
 surface. This vertical surface, therefore, ought to be 
 cut ; and this becomes more especially important if the 
 machine is for heavy work. This can be done by fixing 
 a small vertical knife (i. e . , with a vertical cutting edge) 
 immediately in front of each chisel. The work that has 
 to be done by such a knife is extremely light, and the 
 knife may, therefore, be made a very thin blade which 
 merely slices out the circumferential boundary of each 
 new annular shaving that is removed. It is, of course*, 
 important to set this knife, so as not to cut below the 
 surface tooled by the chisels. The same object may be 
 attained by rounding off the outer corner of each chisel 
 with a round resembling that put on the corners of a 
 jack-plane iron, only shorter and sharper. This arrange- 
 ment is, however, not so economical in power, and has 
 in no other respect superior advantages. The material is 
 taken off in a series of very thin broad shavings (the 
 breadth being equal to the length of the round) instead 
 of in one thick shaving of very small width. 
 
 Messrs. Ransome & Co., in the machine illustrated on 
 p. 34, effect the same object by having in advance of the 
 horizontal-edged finishing chisels a number of gouges, 
 which rough out the surface and do all the hard work. 
 They have six tools in the disc, four of which are gouges, 
 and two finishing chisels. The gouges are simply pieces 
 of cast-steel tube, the ends of which are ground to sharp- 
 cutting edges. This form of gouge has the very great 
 
38 
 
 CUTTING TOOLS. 
 
 [Chap. III. 
 
 advantage of being readily turned round through a small 
 angle when the part of the edge last used has become 
 blunt. Thus a fresh bit of cutting-edge (what is in fact 
 a new tool) is presented for work, and the machine 
 can thus be run for a very long time without being 
 stopped for the sake of taking out and re-grinding the 
 cutters. 
 
 7. Cross Strains through the Machine. — The cutting- 
 sweep of the tools is across the length of the log operated 
 upon, and, therefore, across the grain. This is an advan- 
 tage for heavy, deep cutting, as it precludes the possi- 
 bility of splitting along the fibre in front of the tools. 
 Thus, this style of machine is specially adapted for heavy 
 rough work. 
 
 The resistance to the cutting is also, of course, across 
 the centre-line of the table. This throws a heavy side- 
 stress both on the bed and on the standard which sup- 
 ports the bracket and bearings for the vertical spindle. 
 These must be designed so as to give ample strength and 
 stiffness to resist not only breakage, but also any sensible 
 deflection or harmful vibration in the direction of these 
 forces. At the same time this stress resisting the cutting 
 action being mostly crosswise results in the force required 
 to feed up the timber being comparatively small. This is 
 another reason why this machine is specially suited for 
 heavy work. 
 
 8. Pitch of Chisels in Horizontal Spindle Machines. 
 — In wood-planing machines with the rapidly revolving 
 spindle lying horizontally, the timber passing underneath 
 parallel to the axis of the spindle, the cutting chisels are 
 screwed into recesses in a cylinder the axis of which co- 
 incides with that of the spindle. The chisel edges are 
 parallel to this axis, and they must have a width at least 
 as great as that of the planks to be planed. 
 
 Their bevel and angular pitch to the surface they have 
 to plane is about the same as those last mentioned. Being 
 used for lighter cuts, the pitch might safely and with 
 advantage be made less, but the arrangement of four 
 
Pig. 13.— Wood Planing Machine with Horizontal Cutter-Block, by Kansome and Co. 
 
40 CUTTING TOOLS. [Cliap. III. 
 
 chisels in grooves cut in a small cylinder of some live or 
 six inches in diameter would be impossible at a smaller 
 angle to the tangent. 
 
 9. Ransome and Co/s Wood-planing Machine. — 
 
 A machine of this sort by A. Ransome and Co. is shown 
 in Fig. 13. The block that carries the cutters is of cast 
 steel. The edges of the cutters being set at from 2-F' to 
 3" from the centre of the spindle, the rate of revolution 
 of the block should be about 4,000 turns per minute 
 in order to give a cutting speed of 6,000 feet per 
 minute. This is about the highest speed at which it has 
 hitherto been found practicable to run a spindle without 
 the bearing becoming hot. Fig. 14 shows to a larger 
 scale than that of Fig. 1 3 the cutter block with its spindle 
 and bearings. 
 
 The bearing is made of the hardest gun-metal. It is 
 of essential importance to get the two bearings with 
 mathematical accuracy exactly in line with each other. 
 The brasses should, therefore, be first carefully fitted in 
 their seats in the sliding head-stock, and then, the covers 
 being firmly bolted down, they should be bored out in a 
 boring lathe with one setting only for the two. 
 
 10. Steadying Roller. — In Fig. 13 may be seen a 
 small roller in front of the cutter block. The object of 
 this is to press down the plank firmly on the table and 
 prevent it “chattering/ 7 Obviously this holding-down 
 pressure is not applied at a point so close to the cutting- 
 tool-edge as to be of service in preventing splitting, as 
 is the sole of a hand-plane. Its object is to prevent 
 vibration. This would occur if it were not for the roller, 
 because the cutting-edges have a motion which is mostly 
 forwards in the horizontal direction, but which has also a 
 small upward component. This latter has a continual 
 tendency to lift the plank up from the table. 
 
 11. The Feed. — 111 the machine illustrated, the plank 
 is fastened to a travelling table, which is then fed forward 
 by chain or rack .gearing, the speed of feed being capable 
 of variation. 
 
Chap. III.J 
 
 HATE OF FEED. 
 
 41 
 
 Iii other similar machines there is 
 what is called a “ roller ” feed. That 
 is, the plank to be planed is passed 
 between two rollers, either or both 
 of which are driven in rotation by 
 toothed or belt gearing. These two 
 rollers grip the plank between them, 
 and this is pushed forward by them as 
 they rotate. In Kansome’s machine, 
 shown in Fig. 13, a roller feed arrange- 
 ment may be mounted on the travelling 
 table, which is then thrown out of gear. 
 
 If the plank be fed forward at the 
 rate of 20 feet per minute and the 
 spindle make 4,000 revolutions per 
 minute, the advance per revolution 
 will be 4 ^ 00 ^ wo ft* = 0*06 inch. If 
 there be two blades in the block the 
 depth of each cut will, therefore, be 
 0* 03 inch, and with four blades it 
 would be no more than 0*015 inch. 
 This is just the thickness of a shaving 
 that can be easily taken with a jack 
 plane, and in consequence of the com- 
 bination of this very small depth of 
 cut with the very high speed of cutting, 
 these machines plane up wood surfaces 
 with a high degree of smoothness and 
 “ finish.” 
 
 Here again it is of the greatest im- 
 portance to set the different blades all 
 exactly at the same distance from the 
 centre line of the spindle. If this be 
 not carefully done, not only will one 
 blade do nearly all the work, but also 
 the planed surface will be found 
 covered with a regular series of 
 minute transverse waves or ripples. 
 
 14. — Cutter Block and Spindle for 14-in. trying-up Machine. 
 
42 CUTTING TOOLS. fClnp. III. 
 
 The reason of this is evident. Each time the high-set 
 blade comes into operation it makes a deeper cut than 
 the others, and also the wood travels forward a small 
 distance in each interval between such deep cuts. 
 
 12. Moulding Blades. — By “ profiling ” the edge of 
 the blade, that is, by shaping it, not straight, but so as 
 to fit exactly like a template to the outside of any desired 
 curved or angled section, grooves, tenons, mouldings, &c., 
 can be cut on the plank at the same time as its surface 
 is planed up. Sometimes, when one set of cutters is 
 operating upon the flat upper surface of the timber, the 
 sides are being simultaneously grooved, or tenoned, or 
 beaded, by other cutters driven on vertical spindles placed 
 at either side of the machine. 
 
 13. Tenoning and other Machines. — There is a large 
 class of tenoning, tongueing, grooving, beading, match- 
 boarding, dove-tailing, machines, &c., which are all con- 
 structed on very much the same principle as that of the 
 last described. Their appearance is often much compli- 
 cated by their being arranged with several different tools 
 to do as many different kinds of work, all mounted on 
 the same framing. 
 
 In America, where so much more timber is “ con- 
 verted ” than here, and where manual labour is much more 
 expensive, the designs of such machines show frequently 
 great ingenuity and skill in arrangement of parts, and 
 until lately their workmanship was probably superior to 
 ours y but during the last ten or twelve years great 
 advance has been made in the excellence of manufacture 
 of wood-working machinery in Europe, and those built 
 in England and France cannot be surpassed in arrange- 
 ment, solidity, and superior workmanship. In this 
 class of machinery, more than in any other, first- 
 class workmanship, most especially in the spindle bear- 
 ings,' is of immense importance in ensuring clean, true 
 work, and in giving durability to the machine itself. 
 
4 3 
 
 CHAPTER IY 
 
 SAWS AND MILLING MACHINES. 
 
 A class of machine-tools very much resembling in prin- 
 ciple that dealt with in the preceding chapter, includes saws 
 for wood, saws for iron, and milling machines for metal. 
 
 1. Difference from Machines of Chap. III. — Saws 
 for wood of the commoner and older sorts differ from 
 the tools described in last chapter, in having their 
 cutting chisels made all solid together in one piece. 
 This distinction, however, can no longer be made as 
 a general one between saws and other machines, be- 
 cause it is quite common now to have “ inserted” 
 teeth, in large modern circular saws. There remain 
 two essential distinctions, which separate saws for 
 wood and iron from planing machines, but which do 
 not apply to milling machines. These are, firstly, that 
 the object of the tool is not to flatten and true up a 
 surface, but to separate a block of material into two 
 distinct parts ; and, secondly, that in consequence of 
 this being the object, the teeth and blade on which 
 they are set are made as narrow as they can possibly 
 be made consistently with their having sufficient 
 strength to resist breakage. To obtain a maximum of 
 strength with a minimum of width of face, the thickness 
 of the tooth or cutting chisel, measured in the direction 
 of the cutting motion, is made as great as practicable. 
 
 2. Saving of Timber by Thin Saws. — By making 
 the width of face small, two objects of very great 
 importance are attained. In the first place as small an 
 amount of material as possible is converted into saw- 
 dust and thereby almost entirely wasted. This waste 
 in saw-dust does not appear at first sight to be of ex- 
 treme importance when one watches only a few planks 
 
44 - 
 
 CUTTING TOOLS. 
 
 [Cliap. IV. 
 
 being cut. But when one considers that this waste is 
 repeated millions of times in the course of a year in a 
 single saw-mill, the absolute necessity of economy in this 
 direction becomes evident enough. If, for example, a 
 14-inch square log is to be converted by sawing into £ 
 inch planks, if the saw cat away inch only between 
 each plank, 20 planks will be got from the log ; if it cut 
 -§- inch away only 18 boards •§• inch thick can be got out 
 of it; and if inch be lost in saw-dust, then only 17 
 boards will be obtained. Thus in the first case about 9, 
 in the second 17, and in the third about 23 per cent of 
 the timber is lost in the shape of saw-dust. 
 
 If these logs were 12 feet long, then in the first case, 
 there being 21 cuts, each 14 inches deep and inch 
 thick, there will be more than lj (exactly 1-||-) cubic 
 feet of timber converted into saw-dust for every log. In 
 the second case there would be 2f cub. ft. lost ; and in 
 the third 341- cub. ft. would be the waste in saw-dust. 
 
 If now we suppose that a single saw-frame cuts up 50 
 of these logs per day, and works 250 days per year, the 
 losses per year in the above three cases would be 19,150, 
 34,350, and 49,150, cubic feet of timber per annum. 
 Taking this at the price of 2/- per cub. ft., which is a fair 
 average for yellow pine, we find that the above three 
 yearly losses are represented in money by £1,915, £3,435, 
 and £4,915. This example serves to show the extreme 
 importance of saving by making as little saw-dust as 
 possible. 
 
 3. Saving of Power by Thin Saws. — Secondly, it is 
 almost self-evident that the power required to drive the 
 saw becomes greater in simple proportion to the width 
 of the cut it takes. To save horse-power in the steam 
 or water driving engines also, therefore, thinness of the 
 saw-blade is of the greatest utility. Even in hand-saws, 
 the difference in fatigue to the workman is very speedily 
 recognised by any one who tries saAvs of different thick- 
 nesses on the same Avood. 
 
 In the hand-saws used in England the cutting stroke 
 
Chap. IV.] ENGLISH AND FOREIGN HAND SAWING. 45 
 
 is a push outwards from the shoulder of the workman. 
 This mode of using the tool has been perpetuated by the 
 Anglo-Saxon race in the United States, Canada, and the 
 British Colonies. The blade of the saw is thus thrown 
 in compression , and in order that it may have sufficient 
 stiffness to prevent it buckling, it requires to be made far 
 thicker than if it had to transmit the same force in 
 tension only. This liability to buckle is illustrated by 
 lads beginning to learn to saw, who not unfrequently 
 injure a saw-blade by the unsteadiness of the thrust they 
 give to it, which leads to the teeth catching on one side of 
 the cut and a sharp bend or even a crack being caused in 
 the blade. As it is almost impossible to remedy such an 
 injury perfectly, the saw becomes permanently damaged. 
 On this account chiefly, also, English saw-blades for hand 
 work are (and require to be) made of a much better 
 quality of steel than would otherwise be necessary. 
 
 In Germany, Italy, and most of the European Conti- 
 nent, as well as throughout the chief peoples of Asia, 
 hand-saws are used in tension, the cutting stroke being a 
 pull towards the chest of the worker. In consequence, 
 the blades are made very much thinner than those of 
 English saws, less material is converted into saw-dust, 
 and less exertion is required for a given rate of cutting. 
 
 The English method, however, has this advantage, 
 that a man standing upright can exert a considerably 
 greater force in thrusting forward with his arms than he 
 can in pulling inward. This is still more the case if 
 he leans forward over his work, because he can then 
 throw a large portion of his iveight on the saw handle 
 to drive it forward. The result is, that if an English 
 carpenter be pitched against an equally strong German 
 carpenter, each armed with his own tool, the Englishman 
 will saw through as great, or possibly a greater, length of 
 the same thickness as the German will. But the Orientals 
 sit to this sort of work, and, planting the feet against 
 the log being sawn, pull outwards by the contraction 
 of all the muscles of the body. As is well known to us 
 
CUTTING TOOLS. 
 
 [Chap. TV. 
 
 U 
 
 from our familiarity with the English style of rowing, 
 this is by far the most powerful attitude into which 
 the human muscular system can be thrown. Thus, unless 
 the peculiar shape and position of his work compels, say, 
 the Japanese carpenter to assume an awkwardly cramped 
 position, he is enabled, with his thin, broad, saw blade, to 
 get through his work with far less fatigue and w T ith 
 greater rapidity than an Englishman can. 
 
 Thin saws worked in tension, being extremely pliable, 
 are more likely to make a cut that is not quite straight. 
 The thick saw-blade of English or American make has 
 superior stiffness, and, therefore, superior guiding power 
 to keep t the advance of the cut always in the same 
 straight line, but this superiority in guiding power is 
 again neutralised by the fact already mentioned of the 
 thrust tending to bend the blade, while the pull on the 
 thin saw tends to straighten its blade. 
 
 4. Frame, Band, and Scroll- band Saws. — In hand 
 
 and machine frame saws, the thin blade in tension is 
 almost universally used, as also in band- saws. The 
 
 superiority of the thin blade is recognised in France, 
 where the majority of machine-saws used is of the band- 
 saw class. In scroll-band saws the thickness and narrow- 
 ness of the band permit the saw to cut out comers and 
 holes of extremely sharp curvature. 
 
 5. Circular Saws. — Rotating circular saws, on the 
 other hand, are intermediate between the thrust and the 
 pull saws. In them we may imagine successive radial 
 segments of the circular blade to act as spokes of a 
 wheel, and the cutting teeth to be driven through the 
 wood by these spokes. The direction in which they are 
 driven is perpendicular to the spokes, which are, therefore, 
 on the whole, thrown neither into tension nor comj)res- 
 sion, but are simply bent. 
 
 6. Forms of Saw-teeth. — In all hand-saws and in 
 most machine-saws the teeth are made solid with the 
 blade. There is a great number of different shapes used 
 for the teeth, some of which are found better for cutting 
 
Chap. IV. 1 
 
 FORMS OF SAW-TEETII. 
 
 47 
 
 across tlie grain, and others for “ ripping ” in the direc- 
 tion of the fibre, some more especially suitable for hard, 
 and some for soft wood. Fig. 15 shows seven different 
 common forms of teeth. 
 
 The first four shapes are 
 for cross-cutting — a re- 
 ceiving the special name 
 “ peg ” tooth, and b that 
 of m tooth. The fifth (e) 
 is suitable for ripping J\/LJ\/1J\/[_J\/1_J\/1_J\^ b 
 
 soft wood, and, when 
 made of a smaller size, 
 for sawing iron ; f is one 
 of the shapes commonly 
 used in sash-sawing ma- 
 chines, in which logs are 
 converted into planks ; 
 g is a form suitable for 
 a circular saw. 
 
 In Figs. 16 and 17 
 are shown several forms 
 
 drawn to an enlarged 
 scale, and showing the 
 “set” of the teeth. 
 
 7. Setting Saw- 
 teeth. — “ Setting” is the 
 bending of successive 
 teeth alternately to one 
 side and the other. The 
 
 purpose of this is to 
 make the width of the 
 cut greater than the 
 thickness of the blade, 
 so that the blade may 
 pass to and fro without much friction. Greater power 
 being required for cross-cutting than for ripping and the 
 cut surfaces — composed, as they are, of bundles of fibres 
 perpendicular to the surface — being less yielding than 
 
 Fig. 15. 
 
48 
 
 CUTTING TOOLS. 
 
 [Cliap. IV. 
 
 those parallel to tlie grain, a large amount of set is given 
 to cross-cut saws, and very little to ripping saws. The 
 
 C^- 
 
 Japanese Saws. 
 
 WWW* AAAA/W V\AAAOAAAA/VVVV\0/\A s/ 
 
 |>\f JsWVY\ WVVvV s : 7 
 
 b 
 
 sotting is best performed by striking down alternate teeth 
 upon a small anvil specially made for the purpose. 
 
Chap. IV.] 
 
 suiting saw teetii. 
 
 49 
 
 When all the teeth that have to be set to one side 
 are struck down, the saw-blade is turned over, and 
 the others are struck down to the opposite side. The 
 
 teeth are, however, more 
 commonly set over by 
 means of a specially con- 
 structed pair of pliers 
 upon which there is a 
 stop which, as the pliers 
 
 pull the tooth over, 
 
 comes in contact with the 
 blade and thus regulates 
 the angle through which 
 the tooth is bent to the 
 side. Jn filing the teeth 
 to sharpen them, care must 
 be taken to bevel the 
 edges of alternate teeth 
 opposite ways, and in the 
 subsequent setting equal 
 care must be taken to 
 
 bend each set of teeth 
 
 r 
 
 Fig. 16 . (d, e.) 
 
 towards the side of the blade for which it has been 
 sharpened — that is, so that the sharp bevelled edge will 
 lie outwards on the side to which the tooth is bent. The 
 E 
 
50 
 
 CUTTING TOOLS. 
 
 [Chap. TV. 
 
 M tooth is intended to cut both on the forward and back- 
 ward strokes. The opposite sides of the M are, therefore, 
 bevelled in opposite directions. The result is shown in 
 b , Fig. 16. 
 
 The above method of setting is the commonly adopted 
 one, and is called “ spring ” setting. Another style is 
 what is called “ spread ” set. In this the tooth is not 
 bent, hut has its extreme point hammered, or “ swaged,” 
 so as to become broader than the thickness of the blade. 
 This is more suitable for ripping than for cross-cutting. 
 
 If the set is in excess of what is really needed, 
 evidently the “ kerf ” becomes so wide as to allow the 
 saw-blade to lean a little to one side from the direction 
 of that portion of the cut already made. This leads to 
 the saw cutting out a curved surface instead of a straight 
 one, 
 
 8. Inserted Teeth. — In Fig. 17 f shows a form of 
 tooth for a circular saw in which both spring and spread 
 set are used. The latter is so arranged as to spread the 
 point all to that side of the blade towards which the 
 tooth is bent. In the same figure, g and Ji are two forms 
 of “ inserted” teeth that have of late become much used 
 in America. They are used only in circular saws. The 
 mode of fixing them in place is sufficiently evident from 
 the diagram. The advantages of the inserted teeth are, 
 that if a few teeth are broken they can be replaced 
 easily, so as to make the saw once more as good as it 
 was originally; that the diameter of the saw is not 
 reduced by repeated filing in sharpening ; that the teeth 
 may be tempered much harder than the rest of the 
 blade ; and that the separate teeth being all individually 
 forged and ground to gauge — i.e., to one exact pattern — 
 they are of necessity all exactly alike in size and shape. 
 
 The last point is a specially important one. If any 
 tooth in a saw-blade does not stand so high as the 
 general level of the others, evidently it can do no work, 
 and might as well be non-existent. If, on the other 
 hand, its point is too high, it becomes buried too deep 
 
KEOULAElTY in saw teeth. 
 
 51 
 
 in the timber, and either will be rapidly worn and 
 blunted, or else will be broken off altogether. Until 
 it is injured in one of these two ways, it prevents the 
 neighbouring teeth coming into proper action. 
 
 9. Sawdust Space. — If a saw has a cutting stroke 
 of length L, and the spacing between successive teeth 
 be l y then, in the length L, the number of teeth will 
 be p If, in this single stroke, the bottom of the cut be 
 
§2 
 
 ctJTTi&G Tools. 
 
 [Chap. IV. 
 
 advanced a distance, cl , the thickness of the shaving 
 removed by each tooth is d ~ = 1 If the thick- 
 
 ness of the plank which is being cut is less than the 
 stroke of the saw (as it usually is), the volume of material 
 cut away in one stroke by a single tooth equals the width 
 of the kerf (i.e., a little more than the thickness of 
 blade), multiplied by the thickness of the timber and by 
 the depth of shaving. If the thickness of the timber be 
 called t, this volume will be l % t x width of kerf. 
 
 Now, while any tooth is passing through the timber, 
 this amount of material reduced to saw-dust has to 
 be stowed away in the notch between this tooth and the 
 next tooth in front of it. Reduce the area of this 
 notch to a rectangle standing upon the line drawn 
 between the points of the two successive teeth — that 
 is, find the mean depth of the notch, so that its area 
 may be represented by this mean depth multiplied by l . 
 Then, making an allowance for the greater bulk of the 
 saw-dust per unit of weight than of the uncut wood, 
 we should evidently have this : — 
 
 Mean depth of notch = | t x percentage allowance 
 
 for greater bulk of saw-dust. 
 
 Now, other things being equal, of course the depth of 
 cut increases proportionately with the length of stroke, 
 so that 4 would be found always to have the same value 
 for long and for short strokes. But if one supposes the 
 forward pressure put on the saw to be always the same, 
 then this ratio of depth of cut to length of stroke will 
 be smaller for harder woods, and greater for more easily 
 cut woods. On the same supposition it will be smaller 
 the greater is the thickness of the timber to be cut 
 
 O mm 
 
 through ; that is, it will be inversely proportional to t. 
 
 * Tkis is not mathematically exact. Each tooth advances along 
 a line, inclined to the line of the saw by an angle whose sine is 
 
 j-. The exact thickness of the shaving is, therefore, the above 
 
 multiplied by the cosine of this angle, but, the angle being ex- 
 tremely small, its cosine differs very little from unity. 
 
Chap. IV.] DEPTH OF NOTCH BETWEEN TEETH, 53 
 
 Thus the quantity ^ T is approximately a constant 
 
 quantity so long as the same quality of timber is 
 being dealt with in the same way. We infer from 
 this that the mean depth of the notch between the 
 teeth would be the same for widely spaced and for 
 closely spaced teeth, so long as the percentage allow- 
 ance for difference of bulkiness between the saw-dust 
 and the uncut timber is taken the same. Thus, if 
 deeper notches are used with more widely spaced 
 teeth (as is always the case) this means that for 
 them a greater percentage allowance is made than for 
 closely spaced teeth. The chief reason for this is to be 
 found in the fact that the larger saws are meant for 
 heavier work, that the feed pressure applied to their 
 blades is greater, and that, in consequence the saw-dust 
 is coarser. Thus for these the ratio 1 is made greater in 
 
 consequence of the greater feed pressure, and the allow- 
 ance for increased bulkiness of the material when con- 
 verted into saw-dust is also greater on account of the 
 coarseness of this latter. 
 
 The above calculation has been made on the suppo- 
 sition that the length of stroke is greater than the thick- 
 ness of the timber cut. In sash saws, where large logs 
 are cut up into planks, this is not always the case. If 
 it be not so, then to get the volume of wood cut off per 
 stroke by each tooth we must evidently substitute l, the 
 stroke, for t, the thickness of the log. We would then 
 get instead of t simply | L — d, and the rule would be 
 
 that the depth of notch should be simply proportional to 
 the depth of cut taken per stroke, being made greater 
 than the latter depth in a certain ratio indicating the 
 allowance made for increased bulkiness of the saw-dust. 
 
 In an example quoted from American practice by 
 Grimshaw, a sash saw had the spacing between the teeth 
 11". The stroke was 19" and the length of the saws 
 54", so that timber at least 30" thick could be taken in. 
 The maximum depth of cut per stroke for soft wood was 
 
54 
 
 CUTTING TOOLS. 
 
 [Chap. IV. 
 
 1", the minimum for hard wood being f". The depth of 
 the notch was 1 J", the same as the spacing. The mean 
 depth, of course, was much less, probably not more than 
 about half the extreme depth, or about -§". This being 
 much less than the maximum cut taken per stroke, we 
 infer that the depth of notch was much too small ; and, 
 indeed, it is difficult to imagine where the saw-dust was 
 packed away if the depth of cut (1") reported be not 
 one of those pleasant exaggerations in which American . 
 engineers occasionally indulge. If so heavy a cut as 1" 
 per stroke were to be taken, the depth of tooth should 
 have been made much greater, and the spacing at the 
 same time proportionately wider. 
 
 10. Cutting Speed and Feed. — Circular saws are 
 made to cut usually at the speed of about 9,000 feet per 
 minute, but in America it has been found practicable to 
 use one-and-a-half times that speed. Saws running at the 
 higher speeds are ground so as to make the thickness of 
 the blade at the periphery considerably thinner than at 
 the centre. The object of this reduction at the edge is to 
 obtain as little weight as possible at the points where the 
 velocity is highest, in order to reduce the risk of breakage 
 by centrifugal force, and at the same time to obtain as thin 
 a kerf as possible. At such high velocities the periphery 
 vibrates rapidly from side to side through a small range, 
 the consequence being that the kerf cut is much wider 
 than the breadth of the faces of the teeth. The greater 
 thickness at the centre is required for strength. The 
 resistance to cutting acts perpendicularly at the end of 
 the radius, and the maximum bending stress upon the 
 material of the blade is close to the point of attachment 
 to the spindle. On account of the great centrifugal 
 force given by these high speeds, the greatest care must 
 be taken in using inserted “ planer-bit ” teeth to secure 
 them with absolute safety. If they were not perfectly 
 secure, they would fly out with such violence as to kill 
 any man who was struck by one. 
 
 For the same peripheral velocity, however, the cen- 
 
Chap. IV.] 
 
 FEED OF CIRCULAR SAWS, 
 
 55 
 
 trifugal force is less the larger the diameter is. It is. in 
 fact, inversely proportional to the diameter. It is only 
 half as much with a double diameter. It is on this 
 account chiefly that a greater peripheral velocity may be 
 given to large saws than to small saws, and it is by 
 the employment of saws of very large diameter that 
 the Americans are enabled to cut at such a high 
 speed. These large saws, however, are suitable only 
 for rough work on account of the wobbling vibration 
 set up. 
 
 A saw cutting with the peripheral speed of 9,000 
 feet per minute can be fed forward at a rate varying 
 from 30 to 100 feet per minute, according to the nature 
 of the work done. If the feed is 60 feet per minute, 
 then the advance will be = T |- Q - foot = ’08 inch for 
 every foot of peripheral movement. If the distance 
 from point to point of the teeth is 2 inches, i.e, f 
 6 teeth to the foot, the depth of cut for each tooth 
 is evidently *° ¥ s = *013, or T y inch only. At the 
 rapid feed, 100 feet per minute, that is about ly mile 
 per hour, the depth of cut is no more than *022 or 
 y- inch. 
 
 The very rapid feed that can be employed with saws 
 in good order upon the softer qualities of timber is, there- 
 fore, by no means surprising, when considered in con- 
 nection with the very high peripheral velocity. Of 
 course, for cross-cutting the feed cannot be nearly so 
 rapid. Evidently, other things being equal, the more 
 rapid the feed is the more economically, as regards power 
 expended, is the work done. The thicker the shaving, 
 the smaller is the number of cuts to be taken to get 
 through a given length, and the less also, therefore, is 
 the total area of the cut surfaces perpendicular to the 
 plane of the saw-blade. The two opposing surfaces that 
 are cut by the side edges of the teeth parallel to the 
 saw-blade have, of course, the same amount whatever 
 be the rate of feed, so that there is largely increased 
 rate of doing work with the more rapid feed, but the 
 
56 
 
 CUTTING TOOLS. 
 
 [Chap. IV. 
 
 increase is not in so great a proportion as is tlie greater 
 quantity of timber sawn in a given time. 
 
 11. Horse-Power. — The power required for sawing 
 depends very greatly on the condition in which the teeth 
 are kept. It is the worst possible economy to spare 
 labour in keeping the teeth sharp, to their true shape, and 
 all equally high. Saws are most commonly re-sharpened 
 by hand-filing, but they can be more expeditiously and 
 more uniformly dressed by one of the numerous special 
 machines made for the purpose, in which the teeth 
 are ground by a revolving emery disc. Circular saws 
 have to be dismounted, and taken to the sharpening 
 machine. In order to save time, it is necessary to have 
 different blades for the same machine, so that it need 
 not stand idle 'while one blade is being re-dressed. In 
 view of the economy effected by keeping the teeth 
 constantly in good condition, it would probably be well 
 worth while, in mills where much work is done, to have 
 arrangements whereby a small emery-wheel, driven by a 
 rubber band, as a hair-dresser’s brush is driven, could be 
 used to dress up the teeth of circular saws without its 
 being necessary to dismount them. 
 
 The horse-power required for sawing machines varies 
 with the feed, and the horse-power actually supplied 
 to them in common practice depends greatly on the 
 character of the duty to be performed. If the saw 
 is infrequently used, only sufficient power is supplied to 
 enable the work to be done at a slow rate of feed, 
 because in this case the loss of time involved in the 
 slowness of feed is of little importance. But if the 
 saw is used for a constant special duty, if, for instance, 
 it is specially constructed and used for the production 
 of railway sleepers from the rough logs, or for the 
 conversion of heavy timber into planks, since such 
 work goes on continuously, ample power is given to 
 the saw to enable it to be used to its full capacity. 
 The following examples are given on the authority of 
 Grimshaw. 
 
GANG SASII SAWS, OR SAW FRAMES 
 
 rd rP 
 -+3 +3 
 
 0 CD 
 0 • 0 . • 
 r i Tfl r j t/3 
 
 n ©n o 
 «h rP 44 rP 
 
 o 2 o 2 
 
 4= -S &P-S 
 
 rP P . 
 
 .^5.^ 
 
 0 C3 
 
 M £ 
 
 e £ 
 
 M » 
 
 M 0 
 
 44 rd 
 
 O O 
 
 ,p.a 
 
 •S 
 
 s 
 
 TT* 
 
 2 w 
 
 .ts 
 
 O 4-i 
 
 d O 
 Pew 
 
 J* £ 
 
 Or^j 
 
 SO M 
 35 M 
 
 BAND SAWS. 
 
 Width of Blade 
 in inches. 
 
 <D 
 
 n3 
 
 cj 
 
 T—< • 
 
 CH kJ 
 
 | 
 
 P I 
 ca 
 
 O 
 
 Diameter of Saw | 
 Pulley in inches. 8 
 
 Revolutions per 
 minute. 
 
 Feed per minute I 
 in feet. | 
 
 Horse-power used. 
 
 Width of Single 1 
 Belt in inches. | 
 
 Diameter of Driving | 
 Pulley in inches. | 
 
 rd fj 
 
 0 • d) » 
 
 rjj TOC. | TO 
 
 i r» a> 
 
 o9°S 
 
 43 .9 bp. S 
 
 d .9 d 
 
 •g d 
 W QQ 
 
 Width of Kerf in 
 inches. 
 
 Capacity in one day 
 of 10 hours. 
 
 4 
 
 18 
 
 60 
 
 400 
 
 25 
 
 12 
 
 s 
 
 30 
 
 A 1-1 
 
 JL V 
 
 iff 
 
 10 
 
 5 
 
 16 
 
 72 
 
 350 
 
 30 
 
 15 
 
 10 
 
 30 
 
 1 2 
 
 i 
 
 20 
 
 CIRCULAR SAWS. 
 
 [ 
 
 I 
 
 Kind of Teeth. 
 
 Diameter of Saw 
 in inches. 
 
 Gauge at centre. 
 Gauge at Rim. 
 
 Number of Teeth. 
 Spacing of Teeth. 
 
 Revolutions per 
 minute. 
 
 ! 
 
 1 Feed per revolution 
 in inches. 
 
 *3 
 
 0 
 
 M 
 
 44 
 
 O 
 
 +3 
 
 n3 
 
 g 
 
 1 
 
 I 
 
 CD 
 
 w 
 
 d 
 
 0 
 
 £ 
 
 0 
 
 Pc 
 
 1 
 
 0 
 
 m 
 
 u 
 
 o 
 
 M 
 
 HH 
 
 Width of Double 
 Belt. 
 
 1 
 
 Diameter of Driving- 
 Pulley in inches. . 
 
 Capacity in one day 
 of 10 hours. 
 
 Solid . . 
 
 56 
 
 1 
 
 i 
 
 5 7 j 
 
 48 8| 
 
 60 0 
 
 r-<[!SI 
 
 CO 
 
 1 
 
 4 
 
 
 
 24 
 
 12 
 
 1 
 
 Inserted . 
 
 i 
 
 72 
 
 6 8 
 
 i 
 
 72 3J 
 
 680 
 
 i 
 
 12 
 
 1 
 
 4 
 
 
 IS 
 
 23 ' 
 
 1 
 
 t 
 
 
 Solid . . 
 
 1 
 
 . 60 
 
 4 8 
 
 64 2H 
 
 850 
 
 6 
 
 1 
 
 4 
 
 80 
 
 i 
 
 20 
 
 
 i 55 
 
 i 
 
 Inserted J 
 
 60 
 
 i 
 
 6 7 
 
 34 5J 
 
 400 
 
 2 
 
 1 
 
 4 
 
 i 
 
 25 
 
 1 
 
 1 ' 
 
 
 1 I 
 
 
 Inserted 
 
58 CUTTING TOOLS. [Chap. IV. 
 
 All the above saws — sash, band, and circular — were 
 used on pine with the above speeds, feeds, and horse- 
 powers. 
 
 12. Cold-iron Saws. — There is a class of machine tools 
 which, although in external appearance as different as 
 possible from wood saws, are really constructed on essen- 
 tially the same principle so far as the cutting tool is con 
 cerned. These are milling machines for iron, steel, and 
 brass. Intermediate between them and wood-sawing 
 machines are circular saws for metal, and these have more 
 apparent resemblance to the wood saws than milling 
 machines have. Small circular saws of one to three inches 
 in diameter are much used for cutting the slits in heads 
 of screw-nails and metal screws, and also for making slits 
 in various metal articles in the smallware trades. The 
 cutting speed of the teeth is very much smaller than 
 that of wood saws. It is greater for brass than for iron, 
 and greater for iron than for steel. Ho lubricant is used 
 with brass or cast-iron, but with steel and iron oil or 
 soap-and-water are used in order to keep the tool and 
 the work cool. 
 
 13. Hot-iron Saws. — Saws are also used for cutting 
 iron bars to the lengths desired. Except for the smallest 
 sizes, it is necessary to heat the iron to a red heat. The 
 heating softens the iron, and, of course, makes it much 
 more easy to cut it, so that bars and plates two or three 
 inches thick can be cut without destroying the saw teeth. 
 In saws intended for heavy work, the saw is arranged to 
 run through a trough of cold water, in order to keep it 
 cool, and prevent it from losing its temper. 
 
 14. Milling Machines. — Milling machines, as has 
 already been said, are in many respects very different 
 from wood saws. The difference is partly, of course, due 
 to the difference of the materials worked upon, which 
 require a slower cutting speed and greater power. It is 
 also in great part due to the general difference of object. 
 Whereas the saw has for its purpose simply to divide one 
 mass of material from another, the milling machine has for 
 
Chap. IV.] 
 
 MILLING, 
 
 59 
 
 its purpose the shaping and finishing plane and curved sur- 
 faces to the various desired forms. In this it is perfectly 
 analogous to the wood-planing machines, from which it 
 differs in having the cutting tools not inserted but solid 
 with the cutter-block. The cutter-block, or milling 
 wheel, is simply a disc of greater or smaller thickness, 
 and from one up to five or six inches in diameter, on 
 the periphery of which are cut small teeth. If a plane 
 surface has to be cut, the toothed surface of the milling 
 wheel is cylindrical. If notches are to be cut to special 
 forms, such as, for instance, the interspaces between the 
 teeth of wheels, the contour of the axial section of the 
 milling wheel is shaped accordingly, so as to fit exactly 
 into the recesses to be cut out. 
 
 This small sharp-toothed milling wheel is rapidly 
 revolved and moved gradually from point to point over 
 the whole surface that is to be operated upon. At any 
 one instant it operates upon only one line- of what will 
 be the finished surface, the length of this line being that 
 of each of the cutting teeth. In order to bring the cutter 
 successively over all the different portions of the work, 
 two “feed” motions are necessary. These feeds must 
 produce relative motions between the cutting axis and 
 the work, and, so far as the mathematical result is con- 
 cerned, it is a matter of indifference whether the work is 
 held fixed and the cutter-spindle moved over it, or whether 
 the bearings of the spindle are immovable, while the 
 work is made to move under the cutter revolving in 
 them. The one of the two feeds must produce relative 
 motion perpendicular to the axis of the spindle, either in 
 a straight or in a curved line, according to the character 
 of the surface to be produced. The other feed is in a 
 direction perpendicular to the first, usually parallel to 
 the axis of the spindle, and always in a plane passing 
 through this axis. If both these feeds are rectilinear 
 the surface produced is plane. Any shape of surface 
 may be produced by a suitable combination of these 
 feeds, and the revolving cutter-tool is usually guided to 
 
60 
 
 CUTTING TOOLS. 
 
 [Cliap. IV. 
 
 cut out any desired sliape by means of a “ copying” bar, 
 the form of which corresponds to that desired in the 
 finished work, and along which one bearing of the cutter- 
 spindle is made to slide. 
 
 Fig. 18 shows a milling machine for plane work. 
 The spindle, upon which the cutter is fixed by means of 
 a strong washer and nut, has upon its end a small three- 
 stepped cone. This is driven by a belt direct from the 
 counter-shaft overhead. The spindle revolves in two 
 conical bearings. These bearings are not made conical in 
 order to take any axial thrust. The actual axial thrust is 
 always small, and it is supported at the flat bearing b, 
 specially provided for the purpose at the back end of 
 the spindle, and which can be screwed up for re-adjust- 
 ment from time to time. The object of making the 
 principal bearings conical is simply to allow of the 
 spindle being drawn back by the adjustable screwed 
 collars after the brasses have worn a little, so as 
 always to have the spindle fitting quite closely in these 
 brasses, and thus to avoid the slightest unsteadiness in its 
 rotation. 
 
 These bearings are placed in a headstock, which is 
 bolted fast to the framework of the machine. The axis 
 of the spindle, therefore, always occupies the same 
 position. The work is fastened firmly to the cast-iron 
 table t. This table has two faces, to suit different shapes 
 of pieces to be bolted to it. The one is horizontal and 
 parallel to the spindle axis. The other hangs vertically 
 like a curtain on one side of the horizontal face. Such a 
 combination of two plates cast in one and intended to 
 bolt work to, is called in the technical language of tool- 
 makers an angle plate, and in this instance it is a right- 
 angle plate. Both faces are perforated with series of rect- 
 angular holes, through which are passed the bolts used for 
 clamping the work down. 
 
 15. Machine Vice. — A very convenient appendage 
 to such a table for small work is what is called a 
 machine vice, an example of which is shown in Fig. 
 
PLATE I. 
 
 Side View. Front View 
 
 Fig 18. —MILLING MACHINE, BY ARCHDALE & CO. 
 
Chap. tV.] 
 
 Machine vice. 
 
 61 
 
 .19.. This vice is bolted to the table, and the work fixed 
 in it. The work has usually to be cut on two, three, or 
 four different faces, and 
 has, therefore, to be 
 several times unfastened 
 and re-set. To do this by 
 simply unscrewing the 
 vice and re-screwing it, 
 is very mucli simpler 
 than to loosen all the 
 clamping bolts required 
 to hold the work steadily 
 by direct fastening to 
 the table. There is, how- 
 ever, one disadvantage in 
 the use of such a vice. 
 
 If two surfaces have to 
 be milled exactly paral- 
 lel to each other, after 
 one of them has been 
 finished, tbe work 19 * 
 
 must be fixed witb this 
 
 finished surface close and accurately pressed down on 
 the horizontal face of the table, or on some face accu- 
 rately parallel to this. If it is fixed in an ordinary vice, 
 during the tightening of the jaws there is always a 
 tendency to lift one or more corners of the work out 
 of contact with the plate upon which it has been laid. 
 To obviate this, Messrs Tangye have introduced a very 
 ingenious vice, in which, by the act of tightening up, the 
 jaws are forced downwards through a small distance and 
 scraping on the sides of the work during this motion, 
 draw down the work with them so as to ensure its close 
 bearing upon the accurately horizontal surface beneath. 
 
 This kind of table and machine vice is also used 
 in exactly the same form in shaping machines to be here- 
 after described, and very similar ones are used in slotting 
 and in drilling machines. 
 
62 CUTTING TOOLS. [Glia-. IV 
 
 16. Mechanism of Milling Machines. — The table 
 slides up and down in dove-tailed grooves on the vertical 
 face of the plate p, which is seen in Fig. 18 attached 
 to the front of the frame. It is raised and lowered 
 by means of a nut and screwed spindle. The spindle 
 is vertical, and has on its upper end a small bevel wheel 
 gearing into a similar bevel on the inner end of a 
 short horizontal shaft. This shaft projects beyond the 
 front edge of the horizontal table an inch or so, and is 
 squared at its outer end for the reception of a hand-crank 
 box-key, whereby the workman may turn the screwed 
 spindle so as to raise or lower the table at pleasure. In 
 some machines a rack and pinion take the place of the 
 screw and nut, but the arrangement shown is in every 
 way more satisfactory, the difference of cost between the 
 two being inappreciable. 
 
 This vertical motion is not one of the two feed- 
 motions previously referred to. It is more properly a 
 “ setting ” motion, whereby the work is brought (by 
 hand) to the required height. If, however, the surface 
 has to be gone over more than once, the table has to be 
 raised between the cuts by the above-described apparatus, 
 and the amount by which it is so raised would be quite 
 properly called “ feed.” 
 
 The vertical plate P slides horizontally (carrying the 
 table with it) along the dove-tailed slides cast on the 
 face of the frame. The plate carries a nut which gears 
 with a leading screw actuated at one end by a ratchet 
 wheel and pawl. The pawl can be reversed so as to 
 traverse the table in either direction, or it may be 
 thrown out of gear altogether, and the leading screw 
 actuated by hand. When it is in gear the table receives 
 a slow regular traversing feed, the amount of which per 
 revolution of the cutter is constant. By using a larger 
 or smaller ratchet wheel, or by altering the throw of the 
 pawl, the rate of feed per revolution of the cutter can 
 be changed. The pawl is attached to a slotted lever 
 which is oscillated by an eccentric and eccentric -rod. 
 
Chap. tV.' 
 
 MILLING! MACHINES. 
 
 63 
 
 The throw of the pawl, and consequently the number of 
 teeth on the ratchet wheel it passes over in each throw, 
 is regulated by the position in the slot of the lever of 
 the point of attachment of the eccentric-rod. 
 
 The second feed motion, which is horizontal and per- 
 pendicular to that last described, is obtained by making 
 the table “ compound ; ” that is, of two parts, the one 
 lying on the top of the lower and sliding on it. The 
 sliding motion is produced by a nut and screw actuated 
 by a detachable crank handle fitting on the squared outer 
 end of the screw-spindle. 
 
 This second feed motion is seldom or never actuated 
 by the machinery, but almost always by hand. In the 
 small sizes of milling machines both feeds are usually 
 hand-moved, although a machine feed in the one direc- 
 tion is extremely convenient. 
 
 Much of the work done on milling machines is cylin- 
 drical, or prismatic, in general outline. First one small 
 strip of the surface parallel to the axis of the cylinder 
 or prism is milled, and then in succession, other exactly 
 similar strips, at equal distances from the axis, are 
 operated on. Such work is conveniently fixed on a 
 mandril or otherwise, and placed between centres accu- 
 rately perpendicular to the cutter-spindle. These sup- 
 porting centres may be on separate brackets, each bolted 
 independently to the table, or they may be both on one 
 casting which has a resemblance to the fast headstock of 
 a lathe, this casting being similarly .bolted down. The 
 traversing feed being put in motion, the cutter will plane 
 off a surface parallel to the line of feed, and, therefore, 
 if the centres have been carefully set, accurately parallel 
 to the line of centres. Between each successive cut, the 
 mandril is revolved on the centres through any desired 
 small or large angle. During each cut it must be firmly 
 prevented from revolving. This may be simply managed 
 by fastening a small toothed wheel on the mandril, and 
 arranging a spring-catch to wedge in between any pair 
 of teeth corresponding to the desired position of the 
 
64 
 
 CUTTING TOOLS. 
 
 [Chap. IV 
 
 work on the mandril. For instance, if the work to be 
 done is cutting out the teeth of change, or other wheels, 
 a wheel is fixed on the mandril with either the same, 
 double, treble, or any multiple of the number of teeth 
 in the wheel to be cut ; and by setting the spring-catch 
 in the proper positions, the division of the wheel to be 
 cut will be accomplished with the same degree of accu- 
 racy, i.e., the pitch will have the same uniformity as is 
 found in the wheel used as a gauge, or u copy.” A more 
 accurate method of obtaining the same division is by fix- 
 ing on the mandril a “ dividing plate.” This is simply a 
 flat plate with a number of small holes drilled in it, 
 corresponding accurately to given aliquot parts of the 
 circle, and into which holes fits a little peg-stop passing 
 through a hole in the centre-bracket. If the desired 
 division of the circle is very simple — for instance, if it is 
 desired to divide it only into, say, 2, 3, 4, 6, 8, 12 parts — 
 the holes are often placed in the cylindrical periphery of 
 the dividing plate ; but if the division desired is to be 
 complicated, so that the necessary holes are very numerous, 
 the holes are placed in its flat face, and for important 
 work such a dividing plate should be made of hard gun- 
 metal or of phosphor bronze, in order to minimise the 
 wear of the holes by the frequent insertion of the stop. 
 By arranging the holes on four or five concentric circles, 
 sufficient room for them is obtained without making 
 their diameter very small, and without making the 
 dividing plate inconveniently large. 
 
 17. Cutting Speed and Bate of Feed in Milling 
 Machines. — The beautifully fine and smooth surface 
 obtained by properly conducted milling is the result of 
 using a high cutting speed and an extremely small 
 thickness of shaving. For finishing cuts, a cutter 
 of about 9” in circumference, or 2j" in diameter, 
 should be run at about 60 revolutions per minute to 
 cut tough wrought steel, about 80 for wrought-iron, 
 120 for ordinary cast-iron, and from 140 to 160 for the 
 various qualities of gun- metal and brass. For smaller 
 
Chap. IV.] CUTTING SPEED AND FEED IN MILLING. 65 
 
 cutters the rates of revolution are proportionately larger. 
 These rates correspond to the cutting speeds given in the 
 following table : — • 
 
 Steel 
 
 Wrought- iron . 
 
 Cast-iron 
 
 G-un-metal 
 
 Brass 
 
 These speeds are intended for very light finishing 
 cuts. For heavy cuts, the speed must be reduced to about 
 one half these amounts. Ordinarily, the speed cone by 
 which the spindle is driven has just three steps, which 
 may be taken to correspond with the proper speeds for 
 steel, cast-iron, and brass. 
 
 The rate of feed in the direction of cutting varies for 
 ordinary work from 40 to 70 revolutions of a four-inch 
 cutter per inch of feed. This, of course, gives shavings 
 of extreme thinness. For example, the circumference of 
 a four-inch cutter being 12|-, and there being about five 
 teeth per inch of circumferential length, the number of 
 teeth in the cutter is, say, 62, and the advance in the 
 coarser of the above two-feed motions corresponding to 
 the passage of one cutting tooth over the surface is x 
 yV = g- 4 :Vo an i nc h > while that in the finer feed is only 
 to x «V = isi o of an inch. 
 
 The rate of feed employed always depends on the 
 character of the work done. The power that can be 
 delivered through the belt friction on the cone limits the 
 rate of feed. The maximum possible within this limit 
 is inversely proportional to the length of the cutting 
 edge of each tooth, because the longer this is, the more 
 power is required for the cut. ' 
 
 Again, the rate of feed that may be used depends 
 greatly upon the shape of the piece of material that is 
 being cut, whether this is or is not so shaped as to offer a 
 stiff resistance to the pressure of the cutter upon it. 
 The quicker the feed, the greater is this pressure, and 
 
 F 
 
 45 feet per minute. 
 
 90 ,, ,, 
 
 105 „ „ 
 
 120 
 
66 
 
 CUTTING TOOLS. 
 
 [Cliap. IV.. 
 
 the greater is the tendency of the material to bencl out 
 of the way of the cutter. If it does bend appreciably, 
 the track cut out by the tool will not be a true reproduc- 
 tion of the shape of the tool. For instance, in cutting 
 teeth of fine pitch on small wheels, the tooth that has 
 been last cut is apt to spring to one side under the tool 
 pressure, if the feed be not very cautiously managed ; 
 and this more especially if the material be brass. 
 
 The feed must also be regulated according to the state 
 of the cutter. If this be blunt, it cannot cut so fast as 
 if it were freshly sharpened. Also, if some of the 
 cutting teeth do not stand so high as the rest they 
 will not perform so much work as the others, and may 
 even do none at all. This throws more work than their 
 fair share on the others, and the rate of feed must be 
 lessened to suit the capacity of the most severely used 
 of the teeth. Cutters very frequently become injured 
 by careless usage in this way, even when they are 
 originally made quite perfect. The workman often 
 sets them on the mandril slightly eccentrically, so that 
 only one half of the circumference actually does any 
 work, and this side becomes more rapidly worn than 
 the other. The cutter then loses its circular shape, 
 and cannot afterwards be made to cut evenly by re- 
 dressing and sharpening. The maximum of injury of 
 this sort is that of the breakage of a number of the 
 teeth. The cost of making or of re-sharpening and 
 dressing cutters being very considerable, milling wheels 
 are usually used for a long time after they have begun 
 to get broken. The rate of feed possible with them is 
 the less the more they are broken. 
 
 18. Sharpening Milling Cutters. — The common 
 method of sharpening the teeth of solid milling cut- 
 ters is to use the file. In order to allow of this the 
 cutter needs to be softened in the fire, and this having 
 been done, it ought to be re-turned to give it once 
 more its accurate circular shape. When the teeth 
 have been properly dressed up, it must be re-hardened 
 
Chap. IV. 1 SHARPENING MILLING CUTTERS. 67 
 
 in oil, or in an admixture of salt and flour in water. 
 The process of re-dressing being thus a long and 
 expensive one, it is extremely important to harden the 
 cutter, so that it will stand the work, and remain in 
 good condition for a long time, and therefore no temper- 
 ing is resorted to. The process of hardening without 
 tempering, and so as not to produce such great hardness as 
 to cause brittleness, and also and more especially so as 
 to avoid the correct circular shape being destroyed in the 
 process, is a very difficult one, requiring delicate manipu- 
 lation and much experience. During dipping the cutter 
 should be kept rapidly revolving round its axis. 
 
 Mr. George Hookham, of Birmingham, has recently 
 applied Tilghman’s sand-blast to the sharpening of 
 milling cutters. The results of his experiments were 
 highly successful, a set of cutters in very bad condition, 
 with many teeth half broken, being re-sharpened to a 
 condition almost as good as when they were new and 
 unused. Each cutter was simply placed loosely on a 
 rod held horizontally a little below the centre of the 
 sand-blast, so that this impinged on the faces of the 
 teeth, and kept the cutter revolving like a small mill. 
 As this process does away with the necessity of soften- 
 ing and re-hardening, it is likely to come into general 
 use. On p. 69 Messrs. Smith and Coventry’s improved 
 system of sharpening these cutters is referred to. 
 
 19. Face-plate Chuck with Milling Cutters. — ■ 
 Milling machines are sometimes used with a face- 
 plate of special construction, screwed on the end of the 
 spindle in place of the ordinary circular cutter. In the 
 face of this plate is a series of small square holes, 
 arranged at equal distances round a circle concentric 
 with the plate. In these small holes are placed small 
 cutting tools, all exactly alike and similar in shape to 
 the tools to be afterwards described as used in boring 
 
 o 
 
 and cutter-bars. A milling face-plate of this sort is 
 shown in Fig. 20. If the work is traversed crosswise, 
 the tools will produce a finely finished plane surface. If 
 
63 
 
 CUTTING TOOLS. 
 
 [Chap. IV 
 
 the work is not traversed, but simply fed up in tbe direc- 
 tion of the axis of the cutter-spindle, a circular groove 
 will be cut of the same shape as the tool edge. If the 
 face-plate have different circular series of holes in which 
 the tools may be fixed, circular grooves of corresponding 
 different diameters may be cut. Circular ends of pieces 
 or plates may also by the same means have their outer 
 
 Fig. 20. — Milling Machine Face-plate. 
 
 edges moulded to any desired profile, by shaping the 
 edges of the tools accordingly. The inner edges of 
 annular plates may likewise be moulded in the same 
 way. All the small tools must be shaped exactly alike, 
 and require to be set uniformly with the greatest care, in 
 order that each should stand out from the surface of the 
 face-plate precisely as much as all the others, and thus 
 do its fair share of the cutting. 
 
 20. Cutting Angles. — The cutting angles of these 
 tools, and of the teeth of the solid circular cutter, may 
 with advantage be made as keen as is possible consistently 
 with the retention of sufficient strength and depth of 
 tool. The angle is from 70° to 80 and the angle of 
 relief, i.e., the angle between the back of the tooth and 
 the face of the work, about 10°. 
 
 21. Traversing Headstocks for Milling Machines. — ■ 
 In many milling machines of large size the work is bolted 
 to immovable tables, while the headstock carrying the 
 
Chap. IV.] 
 
 IMPROVED MILLING CUTTERS. 
 
 69 
 
 cutter-spindle is traversed by a feed apparatus in two 
 rectangular directions over the work. 
 
 22. Improved Milling Cutter, — The accompanying 
 woodcut (Fig. 20) shows the special design of milling 
 cutter used by Messrs. Smith and Coventry, the different 
 
 Eig. 20. — Milling Cutter Tools. 
 
 
 diagrams giving examples of the various forms it may 
 take. The chief peculiarity is that the pitch of the 
 teeth is much larger than in other designs. This enables 
 the spaces to be made large enough to admit the edge 
 of a thin emery wheel, and thus the teeth can be 
 sharpened by grinding the faces only. The shape of 
 the teeth in profile is thus better preserved. The 
 maximum cutting speeds recommended with these 
 cutters are : — Cast-steel, 15 to 30 feet per minute; Cast- 
 iron, 18 feet ditto; Wrought-iron, 25 to 80 feet ditto, if 
 well lubricated ; Brass, 60 to 80 feet ditto. 
 
 In connection with this system Messrs. Smith and 
 Coventry use a specially designed grinding machine. A 
 very small emery wheel is mounted on a slide by which 
 it may be traversed along the edge of the milling cutter, 
 the cutter being held steady by a spring clip while the 
 emery wheel revolves rapidly. Details of this system 
 are described in a paper read before the Institute of 
 Mechanical Engineers in April, 1883. 
 
70 
 
 GUTTING TOOLS. 
 
 [Chap. Y. 
 
 CHAPTER Y. 
 
 PLANING, SHAPING, AND SLOTTING MACHINES. 
 
 1. Planing Tools for Metal. — Tlie next simplest class 
 of tools is that of planing tools for metal — a class which 
 is very comprehensive, and the members of which have 
 certain points of resemblance with the later mentioned 
 of the previous class. Planing tools differ from milling 
 tools chiefly in that they work at a much slower rate, 
 take much heavier cuts, require consequently to be much 
 stronger, and, therefore, are nearly always used singly, 
 and not in series as those of the milling machine are. 
 The principal machines included in this class are — 
 Planing machines proper, Shaping machines, and Slotting 
 machines. 
 
 Planing machines proper are for comparatively large- 
 sized work, and in them the tool is usually held fixed, 
 while the work is made to move under it in a horizontal 
 direction. 
 
 In Shaping machines the work is of smaller size, and 
 the tool performs the cutting stroke while the work is 
 held immovable. The stroke is here also in the hori- 
 zontal direction. 
 
 In the Slotting machines the size of work has the 
 same range as in shaping machines, the tool also makes 
 the cutting stroke, but the stroke is vertical. 
 
 2. Fixture of Tool or Work. — The distinction 
 between the fixture and movability of the work and 
 tool, or vice versd , however, is not consistently carried 
 out in any one of these machines. For instance, in 
 the planing machine, while the main cutting stroke 
 is, as abovesaid, performed by the work, both the 
 traversing feed-motion and the feed perpendicular to 
 
Chap. Y.] 
 
 PLANING ACTION. 
 
 71 
 
 the cut surface are performed by the tool. On the 
 other hand, in slotting machines these conditions are 
 exactly reversed, the feed-motions being always motions 
 of the work and not of the tool. In shaping machines, 
 in which the main cutting stroke is obtained by a move- 
 ment of the tool, the feed motions are sometimes given 
 to the table on which the work is fixed, and sometimes 
 to the headstock carrying the tool. 
 
 3. Action of Planing Tools. — Of these three 
 machines the thickest shavings are obtained from the 
 first, and therefore it is on this machine that one can 
 most readily study the special character of the cutting 
 action of planing tools. 
 
 This action is very different from anything that has 
 yet been described. 
 
 The first observation that one naturally makes in 
 taking up a shaving from a planing machine is the very 
 high temperature to which it has been raised during ‘die 
 process of being cut off. It becomes so hot that it cannot 
 be held in the fingers immediately after it has been 
 separated. The next fact to be noticed is, that the 
 length of the shaving is very much less than that of 
 the surface. It is quite easily seen, even at first sight, 
 that shortening has taken place, but owing to the shaving 
 being broken up into a great number of small fragments 
 of irregular size and shape, the surprising amount of this 
 shortening is not readily recognised at once. If, how- 
 ever, the small bent, twisted, and curled pieces are each 
 carefully measured, and the length each would occupy if 
 bent straight again calculated ; and if these lengths for 
 all the small shavings produced at one stroke of the 
 machine be added up, and their sum compared with the 
 length of the metal surface which they covered before 
 removal, the great difference cannot fail to astonish any 
 one who has not before made a similar exact comparison. 
 In the case of some rolled bar iron that was examined in 
 this way, the author found that the length of the shavings 
 was sometimes less than half that of the uncut surface. 
 
72 
 
 CUTTING TOOLS. 
 
 [Chap. V. 
 
 The whole of this shortening is not due to simple 
 compression of the material in the direction of the stroke. 
 A large portion of it, however, is due to this, and it is 
 readily perceived that the form of the tool is such as to 
 lead to the greatest amount of compression that the 
 material will stand before giving way altogether by 
 crushing. In order to support without breakage 01 
 injury the severe stress that is put upon it, the tool 
 point needs to be made very strong. This means that 
 the angle between its front and back surfaces, the line 
 of intersection of which forms the actual cutting edge, 
 must be made large. Since the back surface must stand 
 clear of the material to be cut, the front surface is 
 unavoidably perpendicular, or almost so, to the direction 
 of the cutting motion. This is the surface which exerts 
 the force that removes the shaving, and it is evident that 
 it cannot, being at right angles to the plane of division, 
 exert any appreciable pressure that tends directly to lift 
 the shaving upwards from the cut surface, that is, to tear 
 it off by direct tension perpendicular to that surface. 
 The force it exerts is wholly, or nearly wholly, parallel 
 to this surface, and the result is that the material of the 
 shaving about to be separated is simply shoved forwards. 
 This results in its very severe compression in this direc- 
 tion. As it is pushed forwards, it is compelled to slide 
 over the layer lying immediately underneath, from 
 which it is thus separated by shearing and not by 
 tensive tearing. But so far this action would result 
 in a mere accumulation of material heaped up in front 
 of the advancing tool. The amount of this accumula- 
 tion, before a regular shaving is formed and broken off, 
 varies with the kind of material operated upon, being 
 greater the softer and more ductile that material is. 
 The mode by which this crushed layer is raised up and 
 thrown to one side has still to be explained. The 
 material immediately in front of the tool is stressed in 
 all directions, and on the different planes or sections that 
 may be imagined lying at different inclinations to the 
 
Chap. V.] 
 
 CUTTING ACTION IN PLANING. 
 
 73 
 
 face of the tool, there exist stresses of different inten- 
 sities and of different kinds. On sections parallel to the 
 tool face the stress is wholly compression, and there is a 
 greater intensity of compression on these sections than 
 on any others. On sections parallel to the cut surface, 
 on the other hand, the stress is wholly shear, and it is on 
 these sections that occurs the maximum shearing stress. 
 On other sections inclined to these two, and lying in the 
 right angle between them, the stress is of a mixed 
 character, being partly shear and partly compression. 
 The intensity of neither shear nor compression is so 
 great on any of such sections as on the first-mentioned 
 rectangular surfaces, but their combination is such that 
 at some inclinations the strength of the material to 
 cohere together is more severely taxed than at either of 
 these two latter where the compression and shear exist 
 separately and singly. At one certain inclination the 
 tax on the strength of the material reaches a maximum, 
 and, of course, it is along this surface that the actual 
 rent or destructive crippling of the shaving takes place. 
 This extends diagonally upwards and forwards from the 
 under to the upper side of the shaving. The small part 
 of the shaving being formed in front of the tool is 
 forced to slide up this inclined section of most complete 
 disablement. It is thus made to ride on the top of the 
 material in front of it, and is forced out of the way of 
 the advancing tool. If the material be very ductile, nc 
 actual visible rent may take place, the metal being only 
 excessively stretched in the immediate neighbourhood of 
 the above-mentioned section. 
 
 The angle at which this plane of collapse, as it might 
 be termed, is formed must evidently depend on the ratio 
 of the shearing and compressive stresses on the two 
 principal sections ; and this ratio depends again on the 
 relative ultimate shearing and compressive strengths of 
 the material. 
 
 For the removal of the shaving it is not absolutely 
 necessary for distinct separation to occur along the 
 
74 
 
 CUTTING TOOLS. 
 
 [Chap. V. 
 
 inclined sections. The absolutely necessary shear is 
 confined to the horizontal surface which is the path of 
 the tool edge. This latter shear progresses continuously 
 from point to point, but on the former sections the 
 splitting is intermittent, the split surfaces being at short 
 irregular distances from each other, and the material 
 between them being merely twisted severely but not 
 actually rent. 
 
 Fig. 21 represents the result of this action. The 
 dotted horizontal line shows the line along which the 
 tool edge is about to advance. The ragged lines across 
 the shaving represent the inclined surfaces along which 
 splitting has taken place. In the position shown one of 
 
 these splits has just occurred along the line bb'. This 
 may not be a perfect split ; that is, the shaving may not 
 actually break off along this line, but may adhere by a 
 few of its still unbroken fibres to the material lying to 
 the right hand, out of which the continuation of the 
 shaving will be formed. But, although not actually 
 broken off, the material is so crippled that the cohesion 
 along the line bb ' is very feeble, and as the took advances 
 further, the layer aa'b'b offers little resistance to the tool, 
 and is pushed forward along with the rest of the shaving 
 above it, without dragging along with it any of the 
 material immediately underneath and to the right hand 
 of the line bb'. The point b' thus becomes pushed above 
 the still undisturbed surface at the extremity of the line 
 cc. Just before the split along bb' took place, the pres- 
 
Chap. V.] CUTTING ACTION IN PLANING. 75 
 
 sure of the tool was transmitted upwards from the small 
 surface ab of application along the layer abb' a, in such a 
 way that it was fairly distributed along the line bb' and 
 spent in producing shear along this line. Just after the 
 crack has occurred, there being no longer any appreciable 
 shearing resistance along this line, the whole effort of the 
 tool becomes concentrated at the point c. It produces 
 shear for a minute distance along the line c F, and severe 
 compression on all the material in the neighbourhood of 
 the point c , and along all the lines lying within the angle 
 c'cf, or rather within the space b'bcF. This material is 
 bound by cohesion to that lying below the line cf, and 
 this bond is not overcome until some portion of the sur- 
 face cf is actually shorn through. Thus the metal close 
 in front of c being pushed forward, drags forward along 
 with it the metal immediately below it. If this continue 
 long before the dragging force is destroyed by the shear- 
 ing through of the first part of cf, it is evident that a 
 small perpendicular crack would appear underneath the 
 tool in the cut surface, which of course it is desired to 
 leave as smooth and free from flaws as possible. Such 
 cracks do actually appear if it is attempted to plane 
 across the laminae of rolled plates of inferior quality 
 where the laminae have not been well welded together. 
 This cracking, if it occur, or tendency to cracking, is 
 evidently the result of tension across vertical sections 
 perpendicular to the cutting stroke. If the shearing 
 strength along cf, that is, along horizontal sections in 
 the direction of the cut, be less than the above tensive 
 strength,'* these vertical cracks will not appear. The ten- 
 dency for them to appear increases with the thickness 
 of the shaving, and decreases with the sharpness and 
 keenness of the tool. 
 
 The latter tendency can be easily understood. The 
 
 * Or, more properly, if the ratio of the former to the latter strength 
 is below a certain magnitude, which may be made the object of mathe- 
 matical calculation, but which it is unnecessary to investigate in a 
 book of the present elementary character. 
 
76 
 
 CUTTING TOOLS. 
 
 [Chap. V. 
 
 break along bb' having just occurred, and the surface ab , 
 therefore, no longer offering any resistance to the motion 
 of the tool, the whole resistance is that offered by the very 
 small surface be. This surface at the first instant is very 
 minute, and gradually increases in extent until the next 
 break occurs. The intensity of the resistance offered 
 per unit of area cannot be greater than the crushing 
 strength of the material ; and, therefore, the whole area 
 being very small, the total force exerted by the tool 
 must be correspondingly small at the first instant after 
 bb ' has been broken. This small force is partly trans- 
 mitted along the line cc, but only a fraction of it goes 
 in this direction, because it spreads out in all directions 
 radially from c. A very short crack may be caused 
 along cc, but it cannot extend far, because at only a 
 minute distance along cc' the force is wholly exhausted 
 in producing shear on this section. Thus at this time no 
 part of the force finds its way as far on the line cc as the 
 upper surface near b'. This, therefore, remains undis- 
 turbed in shape or in position, and the point b' of the 
 previous layer of the shaving rises above it so as to pro- 
 duce the ragged upper surface that is observed on these 
 shavings. At the same time it is to be noted that the 
 layer bcc is severely crushed in the direction cc in the 
 neighbourhood of be , and that the intensity of this com- 
 pression diminishes as the distance from be towards b' 
 increases. This crushing is naturally associated with 
 bulging in the transverse direction, that is, in the direc- 
 tion of the line cba. The bulging, or extension, in this 
 direction diminishes gradually from a maximum at the 
 tuol side abc of the shaving to zero at the ujDper side a!b\ 
 Now the result of stretching one surface of a bar while 
 the opposite one is kept at its original length is to bend 
 the bar. This is the cause of the shaving curling up. 
 
 As the tool progresses, the surface be on which it 
 presses becomes larger, the force exerted increases, the 
 thickness of the layer be becomes greater, so that this 
 layer has greater strength to transmit the force forward 
 
Chap. V.] 
 
 CUTTING ACTION IN PLANING. 
 
 77 
 
 towards tlie upper side of the shaving, the transmission 
 of the force reaches farther in this direction, and the 
 strain on the metal near the upper side becomes greater 
 and greater. Still, as the force is generated at be , and is 
 expended gradually in producing shearing strain along 
 the surface cc', the compression is always greatest at the 
 face of the tool, and always diminishes to zero near the 
 point b'. The shearing strain close to the point c on the 
 plane cc' is developed to its full extent almost instantly 
 after the breakage along bb' ; it then extends gradually 
 to successively higher points on the line cc', until it 
 reaches the outside of the metal ; but at this point it 
 never reaches nearly so great an intensity as it does at 
 the base of this same line, and the intensity diminishes 
 gradually from the base to the outer extremity of it. 
 The severity of the shearing stress is measured with, at 
 any rate, some approach to accuracy, by the angle through 
 which the material becomes twisted.* ISTow the line be 
 originally lay along the line gc. Thus the angle between 
 cc and cb , or between bb' and ba was, before the cut was 
 taken, equal to gcc', and has now been reduced to acc. 
 The whole of the material lying on that side of the 
 shaving next the tool is twisted through this large 
 angle. The amount of twist suffered on the other side 
 is comparatively small, as may be recognised by observ- 
 ing the points of the ragged edges on this side. The 
 angle of these edges is not much greater than what was 
 probably the original angle between the upper surface 
 Vf' and b'b, or, what is the same thing, the angle c'cf. 
 The average twist throughout the thickness of the shav- 
 ing may, therefore, be taken roughly as equal to half the 
 angle Gca. The power expended in performing this twist 
 forms a large portion of that required to drive the tool for- 
 
 * Tins is tlie correct measure of the strain, and according to Hooke’s 
 law, Ut Tensis sic Vis, the stress is proportional to the strain. This law, 
 however, is approximately accurate only for very small strain, while 
 the strains dealt with above are very large : are, in fact, the ultimate 
 strains the material is capable of standing without breakage. 
 
78 
 
 CUTTING TOOLS. 
 
 [Chap. V. 
 
 ward, and another large portion is that absorbed in produc- 
 ing the compression already explained. It is to be noticed 
 that both of these amounts of work are done upon the 
 under layer of the shaving along the line cf, and are 
 absorbed in altering its shape and density, and that 
 comparatively little is similarly spent in the upper layer 
 along the line 6V. It is this absorption of energy that 
 produces the great rise of temperature, and, therefore, 
 we find that this under surface of the shaving is very 
 much hotter than the other, the latter being heated 
 chiefiv bv conduction from the former. 
 
 t/ «/ 
 
 The amount of shearing work to be done is evidently 
 less the smaller is the angle Gca, that is, the keener the 
 tool is. Also, since the shearing and the compressive 
 stress decrease from a definite maximum at one side to 
 zero or nearly zero at the other, and since the work done 
 is proportional conjointly to the intensity of the stress 
 and the quantity of metal stressed, it is easy to see 
 that more power is needed the greater is the thickness of 
 the shaving. It does not follow that it is in simple pro- 
 portion either to the angle Gca, or to the depth of cut. 
 The ratio of increase with these quantities can only be 
 satisfactorily determined by actual experiment. This 
 has not as yet been done for planing tools for metal, 
 but in a later chapter will be given the results of a long 
 series of experiments made by the author to determine 
 these points for turning tools. Planing tools have a 
 very similar action, but it is impossible to say that the 
 laws of variation are exactly the same in the two cases. 
 
 4. Friction between Shaving and Tool. — One 
 other source of expenditure of power in the process 
 of cutting is the friction between the shaving and the 
 face of the tool resisting the motion of the former 
 as it slides up the latter. The speed with which the 
 sliding takes place is less than the cutting speed, in 
 the same ratio as the shaving is shorter than the planed 
 surface. This ratio depends on the angle c'gf. The 
 outer ragged side of the shaving is, as has already been 
 
Oliap. V.] 
 
 FRICTION IN TOOL CUTTING. 
 
 79 
 
 said, very litfle compressed in the direction bb' , and very 
 little, if at all, bulged out transversely to this direction. 
 The material is here comparatively unstrained, although 
 it has more appearance of being crushed and tom than 
 at any other part of the shaving. It is very nearly in 
 its original condition. The ratio of the length of this 
 side of the shaving to the length on the line 5V, along 
 which it lay before being lifted by the tool, is therefore 
 simply the ratio of the thickness of the layer a'b' to the 
 corresponding length along Vf . This ratio is that of the 
 line b'c ' to b'c in 
 
 Fig 22, where b'c" 
 is drawn parallel 
 to the face of the 
 tool ab. The angle 
 b'c'c" equals b'bF, 
 and the angle b'c'c 
 equals abb', which q 
 is 180° minus the 
 sum of b'bF and 
 abG. Since the 
 
 sides b'c " and b’c are proportional to the sines of the 
 angles opposite them in the triangle b'c’c", and since sin 
 [180° - (b'bF + aba)] = sin ( b'bF + aba), we find that the 
 ragged side of the shaving is shorter than the planed 
 surface in the ratio 
 
 sin b'b f 
 sin (b'bF-\-abG) 
 
 The inclination of b'b depends on the stiffness of the 
 metal being cut, and on the direction of the thrust of 
 the tool, and this direction depends on the inclination 
 of ab. Thus the above ratio depends wholly upon the 
 stiffness of the metal, and on the shape given to the 
 tool. 
 
 The thrust of the tool is not at right angles to the 
 face of the tool, but is inclined to this face at the angle 
 whose tangent is the coefficient of friction between the 
 
80 
 
 CUTTING TOOLS. 
 
 [Chap. V. 
 
 tool and the shaving. This tangent probably varies 
 from t X q to T % according to the lubrication that is 
 applied. If the lubrication is not good, then unless 
 the angle abG is made much less than 90°, it is probable 
 that the direct thrust of the tool will actually press the 
 shaving downwards instead of helping to lift it up. 
 Tan 23° = T 4 ^-, so that if this were the frictional co- 
 efficient, the angle of the tool-face, namely Gba, could 
 not be more than 90° — 23° = 67° in order that the 
 tool -thrust should not be directed downwards, i.e. 9 below 
 the horizontal line. 60 Q is a commonly used angle for 
 the edges of tools for wrought iron, and as 6 Q or 7 ° 
 is ample for the angle of relief, i.e. 9 between the line Gb 
 and the under surface of the tool, it is probable that in 
 these planing tools the thrust is nearly horizontal if no 
 lubricant be used. 
 
 If, however, the friction be reduced to a minimum by 
 injecting a lubricant between the shaving and the tool- 
 face, the thrust of the tool may with sufficient accuracy 
 be calculated as the requisite horizontal thrust divided 
 by the sine of the angle cibG. If p represent the required 
 horizontal thrust, and f be the coefficient of friction, then 
 the whole friction on the tool face will be 
 
 /* 
 
 sin abG- 
 
 The amount of work done in overcoming this friction 
 during the advance of the tool through unit length is 
 thus : 
 
 /V in b'b~p 
 
 p 
 
 sin ah g sin {b'bF + abG) 
 
 The whole work done in the same time is P, and the 
 ratio of the work lost in friction to the whole work is 
 
 / sin b'bF 
 
 sin abG sin (b'bF-\-abG) 
 
 In order to make this friction as small as possible, it is 
 advisable in the first place to make f small, of course, 
 
Chap. V.] 
 
 LUBRICATION OF CUTTING TOOIS. 
 
 81 
 
 and secondly to make angle b'bF small, and angle abo 
 large. But it must be remembered tliat the above for- 
 mula is only approximately true so long as f is small, 
 and that by making ccbG large we may make p large, that 
 is, increase the whole work done, although at the same 
 time diminishing the proportion of it spent in friction. 
 
 As an example, take the case already cited, in which 
 the angle abo was about 80°, and the shaving only half 
 as long as the planed surface. This would correspond 
 to an angle b'bF about 28°, or rather less than 30° ; and 
 the fraction 
 
 sin b ' bF .k 0 7 
 
 sin ab G sin (//b F+aba) 
 
 The coefficient of friction was in this case probably about 
 so that the work done on friction would be a little 
 more than 15 per cent of the usefully applied work. 
 
 5. Lubrication and Cooling. — The importance of 
 diminishing as far as possible the friction is not confined 
 to a direct saving of power. A large proportion of the 
 heat generated in the cutting operation is due to the 
 friction, and the consequent rise of temperature not 
 only destroys the temper of the tool (if, at any rate, 
 it is allowed to rise to excess) but it also makes the 
 metal more difficult to cut. The tool gets rapidly 
 blunted, and soon requires greatly increased power to 
 drive it beyond what is needed while its edge is still 
 keen. 
 
 Recently experiments have been made with great 
 success on the effect of making a jet of soapy water 
 impinge at a high velocity (produced by high pressure 
 in the supply pipe) upon the point of the tool, and 
 directed from behind the tool forwards to the point. 
 The effect was that a very much faster rate of cutting 
 was found possible without dulling the tool-edge than 
 had ever been attained before. In ordinary lubrication, 
 with the liquid falling in front of the tool, there is little 
 ol* no chance of the lubricant ever reaching the cutting 
 G 
 
82 
 
 CUTTING TOOLS. 
 
 [Cliap. V. 
 
 edge, because the shaving closely pressed down on the 
 tool-face is moving in the opposite direction to that in 
 which it is endeavoured to introduce the fluid. It can 
 thus be effective only as a cooling agent, and not really as 
 a lubricant. When, however, it is injected with con- 
 siderable force from behind, there is in the first place 
 no obstacle whatever to its reaching the cutting point, 
 and once there it seems to be carried up the tool-face 
 along with the shaving which is in course of formation. 
 
 6. Angles of Tool - edge. — The greater the angle 
 of the tool-edge, the larger is the amount of power 
 spent in breaking the shaving in fragments ; the smaller 
 this angle is made, the larger the power spent in 
 friction. At a certain angle, which for all materials 
 is found to be between 50° and 80°, the thrust 
 becomes a minimum. According to numerous experi- 
 ments made by the German, Hart, the angle abG 
 should be 54° for wrought iron, 55 ° for cast iron, 
 and 66° for gun-metal j and the same authority gives for 
 the angle of relief dbG 3° for wrought iron, 4° for cast 
 iron, and 3° for gun-metal. Hart also says that the same 
 angles are best for all depths of cut and for all qualities 
 of tool-steel. 
 
 These angles are from 5° to 10° less than are com- 
 monly used in England, and for very heavy cuts on the 
 planing machine still larger angles are considered advan- 
 tageous. The larger angles are employed in order to 
 give greater strength to the tool, and to prevent the edge 
 becoming so rapidly dulled as it would be with the above 
 keenness. 
 
 It very considerably improves the cutting power of a 
 tool for metal to rub the edge smooth upon any ordinary 
 hone after grinding it. If an emery-wheel is used for 
 grinding tools, it is very important to have a constant 
 stream of water over it, otherwise it is extremely difficult 
 to avoid taking the temper out of the ground edge. 
 
 It is not simply the bottom front edge of the tool 
 that cuts. A most important part of the cutting is done 
 
Chap. V.] 
 
 CUTTING ANGLES. 
 
 83 
 
 at the side of the tool. This is easily seen from Fig 23, 
 which represents the face of the point of a planing tool 
 and the cross-section of the work. 
 
 The dotted line shows the cross-section of the shaving 
 being removed. All round the cutting edge, both on its 
 horizontal and on its nearly ver- 
 tical parts, the hinder surface of 
 the tool should slope away at an 
 angle of 3° or 4° from the cut 
 surface. Thus, if the point were a 
 true circular arc, as seen in the 
 front view, Fig. 22, the back ought Fig. 23 . 
 
 to be part of a true cone. The 
 
 front also ought to be hollowed out to a true conical shape. 
 It would, of course, be impracticable to do this all round 
 on both right and left hand, but as the tool cuts only 
 on one side, it is unnecessary to do it on more than the 
 horizontal lower edge and on the one vertical cutting 
 side. It is impossible with ordinary or simple grinding 
 apparatus to produce the desired true hollow conical 
 surface, but it is not difficult to produce a sufficient 
 approximation to it. 
 
 Considering, however, that an accurate approxima- 
 tion to uniformity of cutting angle all round the cutting- 
 edge is quite unattainable by any ordinary or possible 
 means at the disposal of a workman in an engineering 
 establishment, it is not a little remarkable that the best 
 cutting angles for different materials should have been 
 discussed so keenly as they have been, and that authors 
 and experimenters should be so positive in stating to a 
 single degree what is the best angle, without even 
 mentioning whether they refer to the angle at the bottom 
 of the tool or to that at the side. The tools that are 
 commonly used, and presumably have been used in these 
 experiments, are flat faced, and in this case not even a 
 rough approximation to equality between the angles at 
 different points of the cutting edge is mathematically 
 possible. 
 
84 CUTTING TOOLS. [Chap. V. 
 
 For broad finishing cuts the formation of the lower 
 part of the edge is of most importance. For medium 
 cuts every part is of equal importance, and for heavy 
 cuts the side of the tool is of very considerably greater 
 importance than the other, because the greater part of 
 the length of the cut as seen in cross-section lies at the 
 side and because the bending of the shaving takes place 
 more nearly perpendicularly to the side portion of the 
 cut surface than to the horizontal portion. 
 
 7. Tool-holders. — The tools that have been most 
 commonly used until now are solid square bars of steel, 
 the lower end being forged to the desired shape and 
 ground. These are fastened by one or two set-screws 
 in the front part of the tool-box, an example of which 
 is shown in Fig. 24, A B, the arrangement in this instance 
 being suitable for a planing machine of large size. 
 
 For such solid tools have recently been substituted to 
 a large extent tools made of small pieces of steel inserted 
 in what is called a tool-holder. Of these there is a great 
 variety of patterns, some of which will be noticed in a 
 later chapter in connection with lathes. Of those suit- 
 able for planing machines, the best seems to be that 
 shown in Fig. 25. A small flat piece of steel, of tapered 
 section, of about 1-|" in depth and of thickness at 
 the bottom and T 9 -g at the top, is inserted in a groove of 
 the same shape at the bottom of the wrought-iron bar 
 of square section, which is the holder. This tool-steel of 
 tapered section is now very largely manufactured for 
 machine-tool purposes, and can be got of excellent 
 quality. The groove is made slightly larger than the 
 size of the steel, so as to allow for small irregularities 
 in the size of the latter. The steel is set forward to the 
 desired position by means of the set-screw a; which 
 also takes the thrust of the cut. It is also clamped 
 firmly sidewise in the groove by means of the set-screw 
 b. As the steel is shortened by re-grinding, its edge is 
 maintained in the same position by advancing a. In the 
 diagram the edge is shown considerably in advance of the 
 
Chap.'V.] 
 
 TOOL-HOLDERS, 
 
 85 
 
 vertical centre-line of the shank of the holder. For 
 
 some classes of work, where there is danger of the tool 
 springing into the cut, this would be disadvantageous, 
 but it can be simply avoided by using a shorter piece of 
 steel than that shown, and setting it farther back in the 
 
 groove, the front lower corners of the holder at the sides 
 of the groove being cut away, so as to leave the face of 
 the cutting tool free for the ascent of the shaving. 
 
 The advantages of these tool-holders are evident. 
 In the first place, a very large unnecessary expenditure of 
 costly tool-steel in the formation of the shank is avoided, 
 the whole holder being of forged wrought iron. Secondly, 
 the tool point can be removed for re-grinding with much 
 greater ease and rapidity; and thirdly, this small piece 
 
 of steel can be treated 
 on the grindstone or 
 emery wheel with far 
 greater facility and 
 exactitude than a 
 large and clumsy 
 piece. There is also 
 the very important 
 advantage that there 
 is no forging, re- 
 hardening, and re- 
 tempering required 
 with this style of 
 tool. The steel of 
 tapered section is 
 supplied to the work- 
 shops in long bars. 
 Short pieces are ob- 
 tained from the bar 
 
 simply by nicking Fig. 24a. — Vertical Section of Planing 
 and breaking off cold. Machine Tool-box. 
 
 These pieces are then 
 
 ground, hardened, and tempered. If carefully used, they 
 need never be again tempered until the time when they 
 
86 
 
 CUTTING TOOLS. 
 
 [Cha^. Y. 
 
 have been so often re-ground for sharpening that they 
 have become too short to be of further use. The temper- 
 ing of such small pieces is also much more easily and 
 accurately performed than is that of the points of long 
 bar-tools. 
 
 8. Tool-box. — In Fig. 24 the binding straps zps t are 
 tightly dove-tailed into the front of the tool-box. Each 
 contains one clamping screw. In Fig. 28, page 95, 
 which shows a similar tool-box for a shaping machine, 
 the only modification of this part is that the screws, 
 instead of passing through separate binding straps, 
 penetrate a projection cast on the front piece of the 
 tool-box. 
 
 This front piece, marked 2 , is hinged on a long 
 horizontal bolt seen clearly in the sectional plan b, 
 Fig. 24. It swings loosely on this hinge, so that the 
 tool-point may be drawn forwards, although it cannot 
 be pushed farther back than is shown in the figure. 
 The object of this is to allow the point to be slightly 
 raised during the back stroke when no cutting is being 
 done, so as to press only lightly against the surface. If 
 it were kept rigidly down against the metal while going 
 backwards, the rubbing action would slightly bend over 
 and dull the cutting edge. Even with the above hinge 
 arrangement, the rubbing that still takes place under the 
 pressure caused by the weight of the tool and the swing 
 flap in which it is screwed is injurious to the edge, and 
 some tool-makers put a balance-weight on this flap, which 
 has the effect of tilting it up during the back stroke, so 
 as to entirely clear the tool edge of the work, while the 
 resistance to the cut brings it down to its proper cutting 
 position during the forward stroke. The tool edge must 
 be prevented by a stop from being raised by the balance- 
 weight to a greater height above the surface than the 
 depth of the cut, otherwise it would not catch the metal 
 at the beginning of the new cut in its forward motion. 
 
 The plate y to which z is hinged rests on the front 
 vertical face of the plate x. It is fastened thereto by 
 
Chap. V.] 
 
 TOOL-BOX OP PLANING MACHINE. 
 
 87 
 
 two bolts seen in the vertical section. The lower bolt 
 
 forms an axis round which the whole plate y can be 
 
 swivelled in front of x through a certain limited angle. 
 
 This is possible in consequence of the upper bolt passing 
 
 through a circular slot whose centre coincides with the 
 
 lower bolt. By tightening 
 
 the upper bolt the plate 
 
 may be fixed in any desired 
 
 position. The object of 
 
 this circular motion is to 
 
 make it possible to throw 
 
 the tool-point to one side 
 
 of the tool-box so that no 
 
 part of this latter will in- * 
 
 terfere with the planing of 
 
 vertical faces on the work. 
 
 If the tool-point were not 
 
 thrown to one side in this 
 
 way, then the top edge of 
 
 the vertical face on the 
 
 work to be planed could 
 
 not be higher than the bot- Pig. 24b.— Horizontal Section of Planing 
 . -i ° « . i -i Machine Tool-box. 
 
 tom edge oi the tool- box. 
 
 There passes vertically 
 
 through the plate x a spindle, 5, screwed with a square 
 thread, and having on its upper end a hand- wheel, 
 by which it can be turned. This screw gears in a 
 gun-metal nut which has bearings on the plate w 
 which prevent it (the nut) moving along w in the 
 direction of the screw. These bearings, however, allow 
 the nut to rotate, and at its lower end there is 
 formed on the nut a small mitre-wheel, y. This gears 
 along with the similar mitre-wheel y n fixed on a horizontal 
 freely-rotating bolt at the other end of which gears the 
 other pair of similar mitre-wheels, /h and /3. This last, /3, 
 slides along a horizontal shaft extending to the side of 
 the planing machine, and is forced to rotate along with 
 this shaft by having a feather sliding in a groove cut on 
 
88 
 
 CUTTING TOOLS. 
 
 fCliap. V 
 
 the shaft throughout its whole length. If this shaft' dot's 
 not turn, the nut on the screwed spindle 8 cannot turn, 
 and if the spindle be then turned by hand by means of 
 the wheel at its upper end, the spindle will rise in front 
 of the plate w, and will, by means of the collar near the 
 top of it, lift x, y and z and the tool along with it. In 
 this motion, the plate x is guided rectilinearly by a straight 
 dovetailed groove with internal wedge-shaped packing- 
 strips. If, on the other hand, the hand-wheel be held 
 steady and prevented from turning, then by turning the 
 long grooved shaft from the side of the machine the gun- 
 metal nut will be turned, and the result will be, as before, 
 to raise the whole front portion of the tool-box. This 
 latter mechanism is worked mechanically by a ratchet- 
 wheel and pawl, moved once for each stroke of the 
 machine, so as to give a self-acting feed to the tool in 
 the vertical direction. 
 
 The small horizontal pin on which the mitre-wheels 
 y and /3i are fixed, rotates inside another pin of large 
 diameter and concentric with it. This larger pin forms 
 part of the casting of the circular plate w, and it fits in a 
 round hole in the rectangular plate v. Round this pin 
 the former plate may rotate in face of the latter one. It 
 is fastened in any desired position by the four clamping 
 T-headed bolts, two of which are shown in the horizontal 
 section. The slide plate x with its feed-spindle 5 can, 
 therefore, be fixed at any inclination to the vertical, so 
 that the feed may be in the proper direction to plane any 
 oblique surface on the work. 
 
 Finally, the rectangular plate v slides horizontally on 
 the plane front surface of the hollow beam u , the cross- 
 section of which is seen in the vertical section of Fig. 24, 
 and again to a smaller scale on Fig. 26, Plate II. This beam 
 stretches transversely over the table from side to side of 
 the planing machine, so that the tool-box may be brought 
 into any transverse position over the table. The sliding 
 motion to effect this is actuated by a long horizontal 
 screw, a, lying in the hollow face of the beam, and directly 
 
Chap. V.] 
 
 QUICK RETURN MOTION. 
 
 89 
 
 underneath the grooved shaft that drives the before- 
 mentioned mitre-wheels. This transverse feed-motion- 
 screw is worked at its one end by a ratchet and pawl 
 which is made to have one throw per stroke of the 
 machine, and the extent of which throw, i.e., the number 
 of ratchet-teeth moved over by the pawl, and conse- 
 quently the fraction of a turn made by the feed-screw, is 
 regulated by the point of attachment on the slotted 
 pawl-lever of the connecting-link which works it. 
 
 The tool-box for a shaping maching, or for a small 
 sized planing machine, as shown in Fig. 28, is arranged 
 on precisely the same principles, and differs only from 
 
 that already described in its having fewer adjustments, 
 and therefore consisting of fewer parts, and being 
 throughout much simpler in construction. 
 
 9. Quick Return Motion in Planing Machines.— 
 In all planing machines proper the tool is kept fixed 
 during the stroke, and the work is moved under- 
 neath it. This movement is a back and forward os- 
 cillatory one, and in the common form of the machine 
 cutting is done during one half of the oscillation. The 
 speed of cutting being from 15 to 20 feet per minute 
 only, each half oscillation occupies a considerable 
 fraction of a minute ; and as the time occupied by the 
 back-stroke is wasted, this back-stroke is made to take 
 place at a threefold or fourfold faster rate than that of the 
 cutting stroke. The means by which this is managed 
 
90 
 
 CUTTING TOOLS. 
 
 [Cliap. V. 
 
 may be seen in Fig. 26. This shows (a) a longitudinal 
 section, and (b) a vertical cross-section, of a planing 
 machine, with a maximum stroke of 3 metres (10 feet) 
 capable of planing a surface 1 metre (3 feet 4") wide on 
 a piece of a maximum depth of 1 metre. 
 
 The table on which the work is bolted is marked c. 
 The surface of this is perforated with a large number of 
 rectangular holes, through which the clamping-bolts for 
 the work are passed. This table has two long ridge-like 
 feet stretching its whole length, and by these it rests in 
 two v-shaped grooves formed in the top of the bed-plate. 
 Along these grooves the table slides, being actuated by the 
 spur-pinion i gearing in the toothed rack, h , which is 
 screwed to the under side of the table. The pinion i 
 is keyed on a transverse horizontal shaft, on the outer 
 end of which is also keyed a larger spur-wheel, h , This 
 wheel gears into two different pinions g 1 and g on different 
 centres. The first g x drives the wheel h during the back- 
 ward non-cutting stroke. It is either keyed or cast on 
 the end of a long hollow boss, that runs loose on the shaft 
 upon which the three pulleys d d l d n are mounted. This 
 boss is in one piece with the nearest of these three 
 pulleys d v The driving belt runs over these pulleys, 
 and is shifted from one to another by means of a fork 
 moved by a rod and bell-crank lever, actuated by stops 
 bolted to the under side of the edge of the table. These 
 stops can be bolted in any desired positions, to suit the 
 stroke that is needed for the particular work to be per- 
 formed. At each end of the stroke the bell -crank lever 
 is struck and thrown through a certain angle by one or 
 other of these stops, and this movement throws the 
 driving belt from the pulley d l over the pulley d u (which 
 runs also loose on the shaft) on to the pulley d , or vice 
 versa. When the belt is on d x it drives the table through 
 g { A, i and h. When, during the cutting stroke, the 
 belt is on cl , its motion is transmitted to the table by a 
 much more circuitous route. This pulley is keyed on 
 the shaft which passes through the hollow boss of d x and 
 
Fig. 26.— PLANING MACHINE. 
 
Chap. V.] STARTING BACK AN1) FORWARD STROKES. 91 
 
 g lf and runs transversely under the table to the opposite 
 side of the machine. About the centre of the machine 
 there is keyed on this shaft a pinion e, that gears into a 
 wheel /, keyed on a third shaft lying a little lower down. 
 This third shaft passes towards the pulleys to the outside 
 of the machine, and has keyed on its end the pinion g, 
 which has already been mentioned as one of the two 
 pinions gearing with the wheel h. By this roundabout 
 method, with two reductions of speed at the pair of wheels 
 e and f and at the pair g and A, the motion and power 
 are transmitted to the table on which the work is bolted. 
 The number of teeth in the wheel f is thrice that in the 
 pinion e in the special example in Fig. 26, and the 
 pinions g L g are of the same size, so that the back-stroke 
 takes place at a speed thrice faster than the forward 
 stroke. 
 
 10. Acceleration of Momentum at Beginning of 
 Stroke. — The table and the work upon it together having 
 a very considerable weight, they possess a large amount 
 of momentum even at the slow rate of 17 feet per 
 minute, and cannot, therefore, be reversed in their 
 motion quite suddenly. It is partly in order to allow 
 a brief interval of time to elapse between the instant 
 at which the driving force applied by the belt is taken 
 off the pulley d l which moves the table backwards, and 
 the instant at which the same force is applied to the 
 pulley d which moves it in the reverse direction, that 
 the loose pulley d n is placed between them. Also, when 
 it is desired that the machine should stand still while the 
 counter-shaft is running, the fork is so placed as to keep 
 the belt upon the loose pulley. 
 
 ISTo mass can attain even a small velocity quite 
 instantaneously, and in this case we have a very Jar ge 
 mass, which therefore requires two or three seconds to 
 acquire the full velocity of the stroke, even when urged 
 to it by the full power that the belt is able to exert 
 through the friction between it and the surface of the 
 pulley. At the begining of the stroke, therefore, 
 
92 
 
 CUTTING TOOLS. 
 
 [Chap. Y. 
 
 (whether backward or forward) the belt slips a little, 
 and there is a gradual quickening of the speed of the 
 table as the slipping of the belt becomes less and less. 
 Also, during these first instants, all the driving power is 
 used up in producing this acceleration of velocity. 
 There is none left for cutting the material. It is 
 thus needful to make the stroke of the table several 
 inches longer than the length of cut desired, and the 
 stops must be adjusted so as to give this extra length 
 of stroke. 
 
 11. Reversible Tool-holders. — Even with the above 
 arrangement for quickening the speed of the non-cutting 
 stroke, there is still, of course, a large portion of the time 
 of the machine unproductively spent. In order to do 
 away with this objection, Sir Joseph Whitworth has for 
 many years past constructed his planing-machine tool- 
 boxes so that at the end of each stroke the tool is turned 
 through two right angles round a vertical axis, and is 
 thus thrown into jiosition to cut on the succeeding stroke 
 in either direction. The tool is clamped in a vertical cylin- 
 drical tool-holder, which revolves inside a hollow cylinder 
 made to fit it on the front of the tool-box. Cords attached 
 to the tool-holder and passing over pulleys, actuated by 
 the stops in a similar manner to that in which they shift 
 the fork, reverse the tool. The table is made to move at 
 the same speed in both directions. This arrangement, 
 however, although introduced and approved by the most 
 celebrated tool-maker in the world, has never come 
 into extensive use, and in fact there are inconveniences 
 about it which make the workmen very averse to 
 use it. 
 
 Another system of reversible tools recently intro- 
 duced is more likely to be found practically advan- 
 tageous. In this there is, as in the common system, a 
 hinged flap-plate on the front of the tool-box, in 
 which the tool is clamped. The tool is made with two 
 oppositely directed and exactly similar edges, the bottom 
 surface of the tool joining these edges being at right 
 
Chap. V.J 
 
 REVERSIBLE TOOL-HOLDERS. 
 
 93 
 
 angles to the centre-line of the tool-holder, so that when 
 this centre-line hangs vertically the two edges are exactly 
 on the same level. On one stroke the tool swings back- 
 wards from this vertical position through an angle equal 
 to the proper angle of relief for the under surface of the 
 tool-edge, that is, through 3° or 4°. It is prevented 
 from swinging farther than this exact amount by 
 abutting against the bearing surface provided on the 
 rigid part of the tool-box. On the opposite stroke it 
 swings to the opposite side of the vertical to an angle 
 of the same amount, and is there supported by a similar 
 
 abutment facing the former one. In this simple way, 
 the tool, actuated by the resistance to the cut itself, is 
 automatically brought at the beginning of each stroke 
 into the correct position for cutting in the direction 
 of that stroke. Fig. 27 shows a tool-holder constructed 
 on the same principle as that of Fig. 24, but modified 
 to provide the two opposite cutting edges. An obvious 
 objection to this method is, that both the cutting edges 
 must necessarily lie in front of the point of suspension 
 at the hinge and still more in advance of the point of 
 abutment on the tool-box. If the tool-box and tool- 
 holder be made sufficiently rigid, however, this is not 
 a serious objection for most classes of work. 
 
 If instead of the tapered section of tool-steel a 
 parallel-sided section were used, then the tool-holder 
 
94 
 
 CUTTING TOOLS. 
 
 [Cliap. V. 
 
 might be fixed rigidly, and the requisite rocking motion 
 of the tool in reversing its direction of cutting might 
 take place round the central pin jointing it to the bottom 
 of the bar-holder. In this case the bottom of the groove 
 in which the steel is Inserted would be bevelled 3° or 4° 
 on each side of the central pin, and the whole horizontal 
 thrust on the tool would be transmitted through this 
 pin. To preserve steadiness, it would also be necessary 
 that the vertical sides of the groove should be planed 
 out accurately parallel, and that the tool-steel should 
 be ground accurately parallel and to fit the groove. 
 
 The objection to this and the previous arrangement 
 for a back cutting stroke is, that it is troublesome to 
 grind the two cutting edges of the tool so that the 
 forward and backward cuts will be of precisely the 
 same depth. If these two edges are not exactly at the 
 same distance from the point of suspension, or not 
 at exactly equal distances to right and left of the 
 vertical line through the above point when the tool 
 is pressed against its abutment on the one side and 
 the other, the two cuts will not be accurately of the same 
 depth. 
 
 12. Systems of Driving Planing Machines. — As 
 
 above mentioned, the ordinary system of driving planing 
 machines is through a pinion gearing into a rack screwed 
 to the under side of the table. Each pair of teeth 
 in the pinion and the rack first comes into contact 
 near the point of the rack tooth. The point of contact 
 gradually slides from this point up to near the root of 
 the rack tooth. The pressure exerted between the two 
 surfaces therefore varies slightly in direction, at first 
 having a vertical upward component, and at last being 
 wholly horizontal or nearly so. This produces a minute 
 irregularity in the planed surface, because of the driving 
 force being variable both in amount and in direction. 
 The vertical component at first contact between each 
 pair of teeth relieves a part of the bearing pressure 
 on the guide grooves, and in consequence of the unavoid- 
 
Chap. V.] 
 
 DRIVING PLANING MACHINE. 
 
 95 
 
 able elasticity of materials of construction, this has the 
 effect of lifting the table to a minute degree. To avoid 
 the small imperfections due to these causes in the plane 
 surfaces produced, Sir Joseph Whitworth has en- 
 deavoured to obtain a continuously steady driving 
 force by discarding the rack and pinion, and substi- 
 tuting for them a screw and nut. The nut is fixed to 
 the under side of the table at the middle of its length. 
 
 Pig. 28. — Vertical (a) and Horizontal (b) Sections of Shaping 
 
 Machine Tool-box. 
 
 The long leading screw lies along the centre line of the 
 machine in plan, and stretches the whole length of the 
 maximum desired stroke. This construction is much 
 more expensive than the rack and pinion. Sellars, of 
 Philadelphia, the excellence of whose machine-tools is 
 hardly surpassed by those of any other maker, has 
 adopted a combination of a rack and a screw. His 
 screw shaft lies diagonally underneath the table, and 
 a small portion in the centre of its length only is 
 screwed. A rack is screwed as usual to the bottom of 
 the table along the longitudinal centre line. The teeth 
 of this rack are slightly oblique, like those of a worm- 
 wheel. The degree of obliquity is such that at the 
 
96 
 
 CUTTING TOOLS. 
 
 [Chap. V. 
 
 touching point between the tooth rack and the screw- 
 thread the two surfaces lie in the same direction. It 
 would be as easy to produce this coincidence of the 
 touching surfaces with the teeth perpendicular to the 
 length of the rack. But owing to the friction between 
 these surfaces, the pressure between them is not per- 
 pendicular to them, but inclined at a small angle to 
 that perpendicular direction. The obliquity of the 
 teeth is so chosen that the effect of the friction is to 
 make the driving effort be directed approximately in the 
 direction of motion during the cutting stroke. On the 
 return stroke no cutting is performed, only small pres- 
 sure is exerted, and it is not of great consequence 
 whether it is much oblique to the motion or not. In 
 this arrangement the expense of a long leading screw 
 of large diameter is avoided, and the design is certainly 
 ingenious, but it is difficult to admit that it possesses 
 advantages that make it superior to that of the ordinary 
 rack and pinion. A peculiarity of the gearing is, that 
 the point of contact between the worm-thread and the 
 rack-teeth moves to and fro from side to side of the 
 rack with an oscillatory motion. 
 
 13. Shaping Machines. — When the surface to be 
 planed is short, and the piece of work of which it 
 forms a part is of small size, a shaping machine is 
 used in preference to a planing machine. In this 
 the tool is driven forwards and backwards the length 
 of the cutting stroke, while the work is fixed. Fig. 29 
 shows a side-view of one so designed. The tool- 
 holder forms the outer end of a ram of rectangular 
 section, which slides in a massive guide-box of the same 
 internal section. In a very common form of the machine 
 this ram is driven by a short connecting-rod from a disc 
 crank keyed on a shaft at the back of the machine. On. 
 this shaft is the cone pulley upon which the driving belt 
 runs from the counter-shaft overhead, and, there being 
 ordinarily three steps on this pulley, the machine can be 
 driven at three different speeds. 
 
PLATE III. 
 
 Fig. 29—6' SHAPING MACHINE. (AKCHDALE & CO.) 
 
Cliap. y.] 
 
 SHAPING MACHINE. 
 
 97 
 
 In the machine shown in Fig. 29, however, the ram 
 is jointed to the upper end of an oscillating slotted lever, 
 the fulcrum of which is situated near the level of the ram. 
 In the slot in this lever slides a block bored and bushed for 
 the insertion of the crank pin on a disc crank that revolves 
 on one side of the lever. The shaft which carries this 
 crank lies somewhat below the middle of the height of the 
 lever, and is geared into by a pinion on a shaft carrying 
 the driving cone-pulley. The cutting stroke is performed 
 during the lower half of the crank’s rotation, and the back 
 stroke during its upper half. During the former semi- 
 revolution the crank pin is at a greater distance from the 
 fixed fulcrum of the lever than during the latter. The 
 upper extremity which is jointed to the ram being always 
 at the same distance from the fixed fulcrum, the result is 
 that the forward cutting stroke is much slower than the 
 backward non-cutting stroke, the ratio of the whole 
 length of the lever to that part of it lying between the 
 fulcrum and the crank pin being much smaller during 
 the former than during the latter. This is called a 
 “ quick return motion,” and was first introduced into 
 shaping and similar machines by Sir J oseph Whitworth. 
 Its object is to save part of the lost time in the non-cut- 
 ting stroke. The form in which Sir J oseph Whitworth 
 uses it is more compact than that shown in the illustra- 
 tion. In this latter the crank pin does not pass above 
 the fulcrum of the lever, and the lever is consequently 
 long. In the Whitworth machine a second disc with a 
 slot in its face takes the place of the lever, and the crank 
 pin block slides freely along this slot past the centre of 
 the disc. The second disc has its centre placed higher 
 than that of the first, and drives the ram by means of a 
 crank pin and a connecting rod. 
 
 The work is either bolted to the table or clamped in 
 a vice bolted to the table. This table is a compound 
 sliding table similar to that of the milling machine 
 already described. The bracket on which it rests slides 
 horizontally along dovetailed guide surfaces that form 
 H 
 
98 
 
 CUTTING TOOLS. 
 
 [Cliap. v. 
 
 part of the vertical front face of the standard of the 
 machine. This traversing motion is effected bj means of 
 a leading screw worked by a ratchet-wheel and pawl. The 
 pawl is on a small slotted lever, driven by a light connect- 
 ing rod from a crank pin on that end of the driving shaft 
 opposite to that of the main crank disc. This crank pin is 
 fixed in a T groove across the face of a small crank disc. 
 The rate of this traverse feed can be altered by shifting 
 the end of the connecting-rod in the slot of the crank 
 disc. The ratchet-wheel is coupled to the leading 
 screw spindle by means of a friction cone-clutch. The 
 cone is upon a screw cut on the spindle, and is grasped 
 in the hand by a milled head. A very small fraction of 
 a turn is sufficient to throw it in or out of gear. When 
 it is out of gear, the feed-screw can be turned by a hand- 
 crank placed upon the end of the spindle, which is 
 squared for this purpose. The traversing feed is occa- 
 sionally given to the head carrying the tool and driving 
 shaft and crank, instead of to the table on which the 
 work is fixed, but the arrangement described is the most 
 common. 
 
 14. Circular Shaping. — It is frequently desired to 
 plane portions of cylindrical surfaces in the shaping ma- 
 chine. In machinery there occur frequently cylindrical 
 surfaces which are not complete circumferentially. At 
 one part of the circumference the metal protrudes beyond 
 the cylinder radius. Such surfaces cannot be cut by con- 
 tinuous motion in the lathe, and the plan of rotating 
 the lathe through a part of a revolution and then pulling 
 it backwards, is extremely clumsy and tedious, and it is 
 difficult to produce good work by means of it. The 
 most important examples of this kind of work are the 
 bosses at the ends of cranks and levers. The part of the 
 boss standing above the web is turned in the lathe, and 
 the rest may be finished in the shaping machine if it is 
 of such a size as is admissible. The boss is clamped 
 between two cone mandrils on a spindle whose axis is 
 parallel to the stroke of the tool. Each stroke of the 
 
Chap. V.] 
 
 SLOTTING MACHINES. 
 
 99 
 
 tool thus cuts a straight line on the cylindrical work 
 parallel to its axis : — such a line as is called in mathe- 
 matical language a generating line of the surface. The 
 spindle on which the work is clamped is in gear with the 
 ratchet and pawl feed motion, and is thus rotated through 
 any desired small angle once for every stroke of the tool. 
 The connection between this spindle and the ratchet 
 motion is by means of a shaft parallel to the leading 
 screw and connected with it by spur gearing, and a worm 
 and worm-wheel on this shaft and the spindle itself. This 
 is called the “ circular motion ” of the shaping machine. 
 
 15. Slotting Machines; Tool-box. — The slotting 
 machine is intended for the same class of work as that 
 done on the shaping machine, but in which it is more 
 convenient to place the surface to be planed vertically 
 instead of horizontally. As in the shaping machine, the 
 invariable arrangement is that the cutting stroke is made 
 by the tool, not the work. The line of motion of the 
 tool is invariable, so that all the desired feed motions 
 are performed by the table on which the work is fixed. 
 
 Fig. 30 contains five views of a slotting- machine of 
 good ordinary construction, a is a side elevation ; B, a 
 front elevation ; c, a section parallel to the plane of A 
 through the lower part of the frame and through the 
 table ; p, a transverse central section through the table ; 
 and E, a section through the driving gear h and m. 
 
 The machine shown is designed for a maximum stroke 
 of 11 inches. The whole height of the machine is 6 feet 
 7 inches. It is driven through the cone pulley h, with 
 four steps which give four different speeds, i.e ., four 
 different numbers of strokes per minute, suitable for 
 various metals and for various lengths of strokes. If 
 the counter-shaft be run at 120 revolutions per minute, 
 these different speeds are 13, 23, 39 and 69 double (i.e,, 
 up and down) strokes per minute. With the lowest of 
 these speeds and the greatest stroke, the average linear 
 velocity of the tool would be 2x11x13 inches = 286 
 inches = 24 feet per minute. But, as will be explained, 
 
100 
 
 CUTTING TOOLS. 
 
 [Chap. V. 
 
 the downward cutting stroke is made more slowly than 
 the upward non-cutting stroke, i.e., there is a “ quick 
 return motion.” The tool during its cutting stroke has 
 thus an average velocity of about 21 \ feet, and during 
 its up-stroke a velocity of about 28 \ feet per minute. 
 
 The tool is fixed in the lower end of the long upright 
 casting, b. The projection in front of this casting, seen 
 best in A, has a vertical square hole through it, in which 
 the tool is gripped by the six set-screws, b x . It is thus 
 connected rigidly to the casting b , and since this latter 
 is immovable, except in a vertical line, the tool is not 
 relieved during its up-stroke from close contact with the 
 cut surface. In this respect the slotting machine of 
 ordinary design is at a decided disadvantage as compared 
 with the shaping machine. The difference results from 
 the fact that in the latter machine gravity acts perpen- 
 dicularly to the direction of the stroke, and, therefore, 
 the weight of the hinged tool-holder is easily available to 
 keep the tool in close contact with the metal without 
 much jDressure during the back stroke, whereas this is 
 impossible in the slotting machine of ordinary design, 
 whose stroke is in the same direction as that of gravity. 
 In order that the weight of a hinged tool-holder in a 
 slotting machine should act in the same way as in the 
 shaping machine, the hinge would need to stand farther 
 out in front of the frame than did the centre of gravity 
 of holder and tool that hung from the hinge. This would 
 bring the hinge so far forward as to prevent it from 
 passing below the upper edge of the work, and thus the 
 length of cut would be limited by the length of the tool. 
 A cranked tool might be used to overcome this difficulty, 
 but the weakness introduced into a tool-shaft by a long 
 crank would be a decided objection. # 
 
 In some of the more expensive slotting machines a 
 hinged tool-box is used, which is pressed in one direction 
 by a spring, and is shifted slightly in position at the end 
 
 * The centre of gravity of the hinged part can be thrown back by 
 a counterbalance weight on a small side lever. 
 
Chap. V.] 
 
 DRIVING SLOTTING MACHINES. 
 
 101 
 
 of each stroke by a small cam shaft that is oscillated by 
 striking pallets fixed on the frame. 
 
 For cutting outside faces on work, there would be no 
 difficulty in arranging a hinged tool-box with the too] 
 inserted in a horizontal hole and projecting horizontally 
 so as to clear the hinge. This system would be clearly 
 inadmissible for slotting an inside surface in a confined 
 space, such as a key- way in a wheel-boss ; but in such 
 work it is in any case a necessity to use a tool so long 
 that it will project downwards beyond the bottom of the 
 tool-holder rather more than the length of the cut to be 
 taken, because the tool-box itself cannot usually enter 
 the confined space. There seems, therefore, to be no 
 good reason why a hinged tool-box should not be used in 
 which there are two recesses for the insertion of tools, 
 one of these horizontal for outside work, and the other 
 vertical for inside work. The horizontal tool would have 
 its cutting edge farther from the frame than directly 
 underneath the hinge, and the tool-box would have its 
 abutting surface during the cut higher than the hinge. 
 
 16. Mode of Driving. — In Fig. 30, the already-men- 
 tioned casting, 6, slides up and down in two dovetailed 
 grooves with packing strips forming the extremities 
 of the two horizontal brackets projecting from the 
 standard frame. It is driven up and down by 
 means of the connecting-rod, n. The lower end of 
 this is on a crank pin which is bolted in a radial T 
 groove in the face of the circular disc, m. This is 
 shown distinctly in Fig. E, where the crank pin is 
 lettered m 1 . It is formed with a T head that fits the 
 groove, and can slide along it when the clamping nut is 
 loosened. The pin can thus be fixed at any position in 
 the groove so as to be at different distances from the 
 centre of the disc. This disc is keyed, and rotates along 
 with the shaft g , Fig. e. According to the distance of the 
 crank pin from the axis of rotation, the stroke of the 
 slide b and of the tool held in its lower end is varied. 
 The shifting of the position of the crank pin in the groove 
 
102 
 
 CUTTING TOOLS. 
 
 [Chap. Y, 
 
 can only be accomplished when the machine is not in 
 motion. The driving shaft should be pulled round until 
 the groove lies horizontally, as in this position the pin 
 can be moved in it without the necessity of raising or 
 lowering, except through a very small height, the heavy 
 slide, b. 
 
 The shaft, g , lies in a bush, marked l in Fig. E, which 
 is screwed fast to the standard. This bush has an en- 
 larged eccentric end, which forms the fixed axis round 
 which the spur-wheel, revolves ; k, therefore, rotates 
 about an axis higher than that round which m turns. 
 In the back face of the disc m is cut another radial 
 groove, along which is free to slide a small square block 
 fitting the groove. This block is driven by a crank pin 
 fixed in the wheel k, and entering a hole in the centre of 
 the block. This connection between Jc and m is seen 
 clearly in the section E, where the crank pin in k is 
 lettered k x ; k drives m in rotation by this connection, 
 and during the revolution the crank pin and block k Y 
 slide backwards and forwards in the groove because of k 
 and m not revolving about the same centre. The rota- 
 tion of m is, therefore, not uniform, being faster when 
 the pin \ is nearer its centre, and slower when farther 
 away. During the slow half of its revolution, the tool 
 is descending and doing its cutting work. During the 
 fast half of the revolution it is being lifted and is doing 
 no work. This is the “ quick return,” and is the same 
 as was mentioned as the system adopted by Sir Joseph 
 Whitworth in shaping machines. 
 
 The spur-wheel k is driven by the pinion i, which is 
 keyed on the same shaft as the driving cone pulley. 
 
 VI. Table and Feed Motions. — The construction of 
 the table of the slotting machine is somewhat com- 
 plicated, but is shown clearly in Figs. A, B, c, and 
 D. There are three feed-motions to be given to this 
 table. The first is rectilinear and parallel to the axis 
 of the driving shaft. The leading-screw by which this 
 feed is effected is marked v in the section c, and 
 
Chap, v.-] FEED MOTIONS OF SLOTTING MACHINES. 
 
 103 
 
 its cross-section, and the nut in which it gears and 
 which is screwed to the under side of the plate c , are 
 seen well in Fig. d. The end bearings of this screw are 
 in the base-plate of the standard frame. As it rotates 
 the nut travels along it, and carries with it the whole of 
 the compound table composed of the superimposed plates 
 c, d , and e. The outer squared end of this screw-spindle 
 bears the spur-wheel u L , which gears with the spur-wheel 
 u on the parallel shaft t. This wheel u is not keyed on 
 t , but is connected to it by means of a feather and slot. 
 When it is drawn back along the slot it is put out of 
 gear with u 19 and the shaft t does not then drive the feed- 
 screw v. At the other extremity of t is a pair of mitre 
 wheels gearing it with the short upright hollow shaft r. 
 This revolves loosely on the lower end of the vertical 
 shaft q l9 and is driven by q Y through a pawl, r, on a lever 
 keyed to q x and a ratchet wheel keyed on top of the 
 short hollow shaft. The shaft q v is oscillated by a lever 
 q keyed on its upper end, and jointed by a connecting 
 link p l with a lever p. This lever has on its other 
 end a small pin and roller which runs in the cam groove 
 o. This groove is cut in a casting fixed on the end of 
 the spindle g , already mentioned as being that along 
 with which the driving disc m revolves. Thus the 
 feed-screw v, when it is put in gear by tightening the 
 nut upon the wheel u, receives a small fraction of a 
 turn for each stroke of the tool. 
 
 The second feed motion is also rectilinear, and is 
 perpendicular to the first. It is given to the second 
 plate d of the compound table sliding on the lowest 
 plate c. The feed screw for this motion is marked y Y in 
 the diagrams, and has its end bearings in the plate c, 
 and its nut is bolted to the under side of d. A side 
 view of this screw is seen in Fig. d, and a cross section 
 in C. Figs. A and d show how it is driven by the shaft 
 t. Along this latter slides the mitre wheel w, which 
 is rotated by having a feather fitting in the key-slot, 
 which may be seen (Fig. a) extending nearly the whole 
 
104 
 
 CUTTING TOOLS. 
 
 [Chap. V. 
 
 length of t. A bracket on the carriage makes the mitre 
 wheel travel with it. This mitre gears with the other 
 mitre w x on a short shaft inserted in this bracket, and 
 having on its other end the wheel x. The wheel x gears 
 with the wheel y on the end of the feed-screw y x . It 
 can be put in or out of gear in the same way as has 
 already been described for the first feed-motion. 
 
 The upper plate e is capable of rotation about a 
 vertical axis. In this rotation it moves on the hori- 
 zontal upper face of the plate d which is made in three 
 pieces immovably bolted together, and lias a circular 
 recess turned in it that forms the guide for the top plate 
 in its circular motion. This is the third feed motion. 
 It is called the “ circular motion, 5 ’ and its object is to 
 facilitate the slotting of cylindrical surfaces. The feed 
 is actuated by the spindle z l7 with the spur-wheel z on its 
 end gearing with the wheel x. Either or both of the 
 wheels z and y can be drawn back on their spindles so 
 as not to be in gear with x. When they are desired 
 to be in gear they are pushed forward. The spindle z x 
 has on it a worm, and drives it by a feather sliding in a 
 longitudinal slot. This worm gears into a worm wheel 
 cast on the lower part of the table e , which thus receives 
 a uniform small circular feed per stroke of the tool. 
 
 The table cannot be moved vertically upwards or 
 downwards. The adjustment of the height of the tool 
 to the work it has to cut is effected by bolting in a 
 higher or lower position in the slot of the slide b the 
 block by which this slide is driven by the upper end of 
 the connecting rod n. 
 
 18. Improvements in Planing Machines. — There is 
 given in Fig. 30 # an illustration of a very good form of 
 planing machine by Smith and Coventry of Manchester. 
 One special feature in the design is that the slide 
 bearings of the table are flat instead of being V grooved 
 as usual. A fitting strip at one side can be set up by 
 set-screws so as to make an accurate fit to steady the 
 table side-wise, and to take up the side wear. Also a 
 
Chap. VI*] 
 
 LATHES 
 
 105 
 
 tappet motion connected to the tool-box by cord gearing 
 gives the tool a positive lift of small amount at the end 
 
 Fig. 30*. — Planing Machine (Smith and Coventry). 
 
 of the cutting stroke which effectually prevents any 
 rubbing at all between the tool and the work during the 
 back stroke. 
 
 CHAPTER Y I. 
 
 LATHES. 
 
 1. Primitive Lathes. — The Lathe is so important a 
 machine-tool, does such a variety of work, and has 
 so many different forms, that it requires a chapter to 
 
106 
 
 CUTTING TOOLS. 
 
 [Chap. VI. 
 
 itself. It is by far the oldest machine cutting tool, 
 and its early history is very interesting to those who 
 think it profitable to trace the development of machi- 
 nery in its infancy. The first form which it assumed 
 in Europe may still be seen at work in Japan and 
 other Asiatic countries, where very useful and in- 
 genious, although not very accurate, work is per- 
 formed by its help. The rotation of the spindle is 
 not continuous. It makes a certain number of revolu- 
 tions in one direction during which the tool cuts, and 
 then this motion is reversed through the same number of 
 turns while the tool stands idle. To mechanics who are 
 now so familiar . with the crank and connecting-rod link- 
 work for producing continuous rotation, it may seem at 
 first sight surprising and absurd that the machine should 
 remain for long in such a condition that during half the 
 time it was in motion it did no work ; but it must be 
 remembered that the three kinds of planing machines 
 described in the last chapter are even now in very much 
 the same state of advancement, and that it is not at all 
 improbable that even the next generation of engineers 
 may look upon our present planing machines as being as 
 antiquated and absurdly wasteful of time as these primi- 
 tive lathes appear to us now. 
 
 2. Geometrical Character of Turned Work. — The 
 surfaces cut in lathes are all surfaces of revolution : 
 that is, the finished work has a geometrical axis which 
 has this property, that if sections be imagined to cut it 
 perpendicularly and at all positions along it, the lathe- 
 cut peripheries of all these sections are circular. The 
 diameter of the circle may vary in any manner, so that 
 a longitudinal section taken through the above geo- 
 metrical axis may have any shape, its bounding lines 
 being either straight and joining at sharp corners, or 
 being curved in any manner, or being any combination 
 of curved and straight lines. 
 
 The work being fixed to the rotating spindle of the 
 lathe, and the cutting tool being held steadily against it, 
 
Chap. VI.] 
 
 LATHE FEED MOTIONS. 
 
 107 
 
 the axis of the lathe spindle becomes the above geo- 
 metrical axis of the work, and the tool cuts out the circu- 
 lar peripheries of the transverse sections. In order that 
 the tool should cut successive peripheries, it must be 
 moved parallel to the axis of rotation. In order that 
 it may cut circles of different sizes at different parts, it 
 must be moved nearer or farther from that axis — that is, 
 perpendicularly to it. These two motions of the tool are 
 called feed motions. They may be combined in any ratio, 
 and this ratio may be kept constantly the same or may 
 vary from point to point. The ratio may vary from zero 
 to infinity : that is, the reciprocal of zero. If a shaft has 
 to be turned truly parallel — i.e., of the same diameter 
 throughout its length — the feed motion perpendicular to 
 the axis must be zero, and its ratio to the longitudinal — 
 or, as it is technically termed, traversing — feed motion is 
 zero. If a surface of the work has to be faced truly flat 
 and perpendicular to the axis, the traversing motion must 
 be zero, and the ratio of it to the perpendicular — or, as it 
 is called, surfacing — motion is zero, while the ratio of the 
 latter to the former is infinitely great. If the two mo- 
 tions are combined in a ratio remaining constantly the 
 same, the surface is turned to a conical shape. This 
 shape is referred to as having a straight taper. If the 
 two are combined in a ratio that constantly changes, then 
 a surface is produced that is curved longitudinally. 
 
 3. Hand and Power Mechanism. — The rotational 
 motion of the lathe spindle is always produced by means 
 of some sort of mechanism. The feed motions are given 
 to the tool in the simpler class of lathes directly by 
 hand,, and in the more complicated by mechanism which 
 can be worked either by hand or by the same power 
 that rotates the spindle. 
 
 In lathes for turning wood the feed is nearly always 
 given directly by hand. The exceptions are some lathes 
 specially constructed for the manufacture of one particu- 
 lar article in large quantities, such as reels and bobbins 
 for winding cotton, linen, or silk thread upon. In these 
 
108 
 
 CUTTING TOOLS. 
 
 [Chap. VI. 
 
 theri being no variation in the successive feed motions to 
 be given to the tool, there is an immense saving of time 
 in guiding these mechanically, and in limiting their extent 
 by stops. Thus the required shape is given with certainty, 
 without the necessity of much — or, indeed, hardly any — 
 thought on the part of the workman, and, therefore, 
 is accomplished with extreme rapidity and consequent 
 cheapness. 
 
 In general wood turning, however, an infinite variety 
 of shapes is desired, and the constant change of requisite 
 feed motions for the tool demands the unremitting atten- 
 tion of the turner. There are two special considerations, 
 depending on the character of the material, that cause the 
 direct hand guidance of the tool to be more convenient 
 than mechanical guidance. The first is that the quality 
 varies much more largely and more rapidly from point to 
 point in timber than it does in any metal. When the 
 turner comes to a knotty or cross-grained portion, he 
 must alter the manner of holding the tool to suit the 
 different texture. The tool is keen-edged, and corres- 
 pondingly weak. To avoid the risk of breaking it, it 
 must be delicately managed. The alterations in texture 
 are reached more suddenly in dealing with wood than 
 with metal, not only because the differences lie closer 
 together, but also because the cutting speed is very much 
 greater, and the tool, therefore, passes from one spot to 
 another more rapidly. The second consideration is that, 
 in consequence of this high cutting speed and of the 
 softness of the material, the whole work is performed 
 much more quickly and the necessary successive changes 
 of position and direction of tool feed motion follow each 
 other much more rapidly than in metal turning. There 
 is greater advantage, therefore, in the handiness of direct 
 hand guidance of the tool than there is in the greater 
 accuracy of mechanical guidance. 
 
 4. Tool-rest for Wood Turning. — Fig. 31 shows the 
 hand tool-rest for a, wood-lathe. 
 
 (a) i)s a side view looked at parallelly to the lathe 
 
Chap. VI.] 
 
 WOOD TURNING. 
 
 109 
 
 spindle axis ■; ( b ) is supposed to be seen perpendicularly 
 to the same direction. The horizontal bar, from four to 
 ten inches in length, has an overhanging section. On this 
 the tool is firmly held down with the left hand, while the 
 right grasps the end of the wooden handle. In roughing 
 out a gouge is used — that is, a tool formed as if made by 
 bending a strong flat chisel into a semi-cylindrical channel 
 shape. The right hand traverses the tool-point by sweep- 
 ing it through a small angle round its resting-point on 
 
 Fig. 31. 
 
 the rest as a pivot, then pushing this resting-point a 
 short distance along the rest, and repeating these move- 
 ments alternately. This plan allows the tool to be field 
 more firmly down on the rest than if the point of sup- 
 port of the tool were continually pushed along. In 
 finishing, however, a broad flat chisel with a straight 
 cutting edge is used, and evidently, in giving the 
 traversing feed to this tool it is necessary to keep the 
 cutting edge always exactly parallel to the axis of rota- 
 tion in parallel work, or to the surface of whatever work 
 is being cut. To do this, the chisel must be moved always 
 parallel to itself, and, therefore, the above oscillatory 
 feed motion cannot be given to it, but it must be slid 
 along the rest gradually and continuously. 
 
 5. Tools for Wood Turning. — Among the tools used 
 for lathe turning is the gouge already mentioned. The 
 bevel to produce the cutting edge is ground on the out- 
 side, and at a somewhat greater angle than that used for 
 paring-gouges and chisels. Sectionally, it is of small size, 
 
110 
 
 CUTTING TOOLS. 
 
 [Chap. VI. 
 
 both inside and outside being fashioned to small radii. 
 The end is ground so as to give a cutting edge, not square 
 across the length of the tool, but sharply pointed to an 
 oval curve. Deep cuts of very short axial length may 
 thereby be taken, and a large amount of material 
 turned off without the need of running the tool back- 
 wards and forwards frequently. Finishing cuts are 
 hardly ever taken by means of a gouge, and, in fact, 
 it is impossible to cut the surface with this instrument 
 so as not to leave a series of small ridges between the 
 cuts. The turning-chisel is ground with a bevel on 
 each side, therein differing from the paring-chisels 
 formerly described. It also is much thicker and 
 stronger than these, and has a larger cutting angle. 
 The edge is usually ground obliquely to the length of 
 the blade, and chisels with various breadths and various 
 degrees of obliquity of the cutting edge are used. The 
 advantage of this obliquity is in facilitating the cutting 
 out of sharp corners and in “ cutting in” — i.e., in taking a 
 cut straight into the wood in a plane perpendicular to 
 the axis of rotation. The best finishing tool for wood 
 turning is an old paring-cliisel, which has been by use 
 worn down short to the upper end of the blade where 
 it is tolerably thick and strong and void of spring. In 
 using this in order to take just the last cut, it is a useful 
 practice, after carefully sharpening the edge on the oil- 
 stone, to turn up a minute feather edge by drawing a 
 gouge blade once or twice with considerable pressure 
 across the cutting edge of the chisel. 
 
 A fiat-faced chisel may also be used very effectively 
 in cutting in, with the flat face next the surface which 
 is to be preserved. In doing so, the flat face must 
 be carefully held obliquely inclined to that side of the 
 vertical away from the edge that must be preserved 
 as the finished one. 
 
 6. Tool-rest for Metal Turning. — A tool-rest for a 
 lathe for metal turning is a much more complicated 
 structure. It consists of a series of plates, one on the 
 
Chap. VI.] 
 
 METAL TURNING SLIDE-RESTS. 
 
 Ill 
 
 top of the other, on the topmost of which the tool is 
 firmly clamped by a flat piece pressed down on it by 
 screws. The plates slide one over the other with dove- 
 tail groove slide surfaces. It is therefore called a slide - 
 rest ; and because the motion given to the tool is com- 
 pounded of the sliding motions of the plates one over 
 the other, it is called a compound slide-rest. 
 
 The grooves along which free sliding takes place are 
 all rectilinear. One set is placed perpendicularly to the 
 other, and they are usually placed so that one is parallel, 
 and the other perpendicular, to the centre line of the 
 lathe. But it is sometimes desirable to give the tool an 
 oblique feed motion without having recourse for that 
 purpose to a combination of two simultaneous motions, 
 and therefore provision is made for turning the upper 
 portion of the rest round a vertical axis, so as to set the 
 slide at any inclination to the lathe bed. 
 
 There are two classes of such rests, according to 
 whether or not it is desired to have the feed motions 
 not only mechanically guided, but also propelled by 
 lathe power, and not by hand power. When this 
 power propulsion is applied, there are again two sub- 
 divisions, according to whether both the traversing and 
 the surfacing feeds are actuated by power, or only one 
 of them. The word “ self-acting ” is inserted in the 
 name of the lathe to indicate this power propulsion of 
 the tool in its feed motions. Thus we have self-acting 
 traversing (or sliding) lathes, and self-acting traversing 
 and surfacing lathes. 
 
 When these self-acting arrangements are introduced, 
 it is still necessary for the workman to have power to 
 move his tool either way through a small range by 
 hand for the purpose of setting it, or for manipulating 
 in a rapid convenient manner any short, bevelled, or 
 rounded part of the surface to be wrought. To meet 
 this need the slide surfaces are duplicated, the main 
 slides driven by power being at the base of the rest, 
 while at its top two short slides at right angles to 
 
112 
 
 CUTTING TOOLS. 
 
 [Chap. VI. 
 
 each other are introduced, these being worked solely 
 by hand. Between the upper and the lower pairs comes 
 the circular grooved slide surface, by which the upper 
 slides may be set so as to work obliquely. 
 
 An example of the more complicated of the ordinary 
 styles of slide-rest will now be described. The simpler 
 kinds contain merely portions of this form, one or other, or 
 both, of the self-acting slides being dispensed with. With 
 the disappearance of each set of slides there disappears 
 also, of course, the whole train of mechanism that drives it. 
 
 7. Mechanism of Slide-rest. — Fig. 32 shows a slide- 
 rest of this class. F is a section parallel to the bed of 
 the lathe, and e is a cross-section. 
 
 The topmost piece is a bracket-formed plate. This 
 is held down to the plate n L by a stout bolt, round which 
 it may be swivelled into any position by slackening the 
 nut. Underneath the projecting part of this the tool is 
 laid and fixed down firmly by two square-headed screws, 
 and as this piece may be swivelled as mentioned, the 
 tool may be set at any horizontal angle with reference 
 to the other parts. 
 
 The plate % slides over the plate n underneath it, 
 the pair of guide surfaces being dovetailed in the usual 
 way with a bevelled packing strip. The motion is 
 effected by a screw and nut, the former having its 
 bearings in the upper plate %, and advancing along 
 with it, while the nut is set in the plate n so as to 
 be immovable in it. The screw at its front end, 
 where it is easily accessible, has its end squared for 
 the reception of a crank handle by which the workman 
 turns it. This motion in the ordinary position of the 
 slide-rest is perpendicular to the rotational axis of the 
 lathe. This is the motion most frequently required by 
 the turner to set the tool in to take the desired depth of 
 cut, to withdraw it at the end of a cut in order to slide 
 the whole rest to the other end of the work for the 
 purpose of beginning a new cut, or to withdraw it quickly 
 from its work in case of anything going wrong. For 
 
Chap. VI.] 
 
 LATHE SLIDE-REST. 
 
 113 
 
 this reason, this slide is placed highest. The least weight 
 rests upon the topmost slide, and it is therefore the most 
 easily moved. 
 
 The plate n now slides by a similar pair of dovetailed 
 surfaces over the plate m. This motion is parallel to 
 the lathe spindle, and it is effected also by a screw and 
 nut. The nut is bolted to the under-side of the plate n, 
 and the screw has its bearings in m. This screw is squared 
 at its right-hand end, and is worked by hand, similarly 
 to the upper one. 
 
 The plate m is deeper than, any of the others. Its 
 top part is elongated in the direction of the sliding of n 9 
 and its lower part is flat and circular. The latter fits 
 over a similar surface turned on the upper side of L 
 In two holes in this circular part are fixed two bolts, 
 with hexagon nuts on their upper ends and with dove- 
 tailed heads at the lower ends. These pass into two 
 circular concentric slots of similar section, shape, and size, 
 and cut out in the under part of m. By this means the 
 whole of the rest lying above l x may be swivelled round 
 the short pin seen in the middle of m, and clamped in 
 any position by the two bolts already mentioned. 
 
 The lower plates \ and l are larger in size than the 
 others, and give a greater extent of motion, one along the 
 surface of the other. As may be observed in the cross- 
 section, the nut is bolted to the higher of the two plates 
 l l9 and the screw is placed in the lower one, l. This 
 screw, marked z J9 is a long one, about twice the breadth 
 of the bed of the lathe. There is thus a long range 
 of motion obtainable on this slide. At the end of the 
 screw in front of the lathe the screw spindle is square, so 
 that it may be turned by hand by means of a crank 
 handle. It is driven mechanically by a spur-toothed 
 pinion z upon its extremity at the back of the lathe. 
 This pinion is not keyed fast on the screw spindle, but 
 may slide along it the length of the teeth, and drives the 
 spindle by a feather fitting a key slot in the spindle. 
 
 On an extension cast on the pinion is a clutch groove, 
 2 
 
114 CUTTING TOOLS. [Chap. YI. 
 
 which is embraced by a fork on the end of the rod %, seen 
 In the plans B and G, and in end view in H. 
 
 This rod extends to the front of the tool-rest, from 
 which position the workman can push it forward, and 
 thereby slide the pinion z along its shaft. In one 
 position the pinion is in gear with the spur-wheel u , 
 driven by the worm £, which is rotated by a feather 
 lying in a long groove in the shaft s . When it is 
 not desired that the transverse slide-screw z 1 should 
 move, the pinion is pushed out of gear with u. The 
 shaft s extends the whole length of the lathe, and is 
 driven at the fast head-stock end by means of spur 
 gearing and a narrow belt running over a pair of small 
 stepped cones. Since this belt is apt to slip on the 
 cones to a small and irregular amount, it is evident 
 that the above mechanism is incapable of giving an 
 exact and constant ratio between the u surfacing ” feed 
 of the slide-rest and the rotation of the spindle in the 
 fast head-stock, and of the work that is being turned. 
 The maintenance of exact constancy in this ratio is, 
 however, not of importance. 
 
 The shaft s runs, as has been said, the whole length 
 of the lathe-bed, as may be seen in the plan B. As 
 the slide-rest moves along the bed into new positions, it 
 is necessary that the worm t should move with it. It is 
 therefore compelled to slide along the key-slot in the 
 shaft by a fork bracket bolted on the rest “ saddle,” this 
 fork embracing the boss of the worm. 
 
 8. Along with the boss of the worm-wheel u is 
 keyed a spur pinion, marked v. This pinion gears with 
 the wheel w, seen in Figs. G and H. The wheel is 
 fastened by a feather sliding in a key-slot to a short 
 hollow shaft, on the other end of which is keyed the 
 pinion x. It is also pinned to a rod which lies in 
 the interior of this hollow shaft and is continued to 
 the front of the slide-rest. By means of this inside 
 rod the wheel w may be pushed back so as not to be 
 in gear with the pinion v , when also the pinion x will 
 
Chap. VI.] 
 
 TRAVERSE FEED MOTION. 
 
 115 
 
 therefore not be moved by the rotation of the shaft s 
 with the worm t; x gears with the toothed rack y, 
 which is bolted on brackets, seen in the cross-section 
 E, to the back cheek of the lathe-bed. Thus when s 
 is in motion, and also in gear with x, this pinion travels 
 along the rack, and since the shaft on which it is keyed 
 has its bearings in the saddle of the slide-rest, the latter 
 is carried along the bed, or “ traversed.” 
 
 The self-acting traverse motion is slightly irregular, 
 not only on account of the above mentioned slipping of the 
 belt driving s , but also because the teeth of a rack are 
 never spaced with exact mathematical uniformity. But 
 for ordinary parallel turning it gives a perfectly sufficient 
 degree of constancy to the feed motion, and a much 
 higher degree than could be obtained by hand. There 
 is one important advantage in having this gear driven 
 by a belt. In roughing out work in the lathe, the 
 depth of cut always varies to a slight extent, owing to 
 the irregularity of the outside surface of the casting 01 
 forging that is being turned. There are also here and 
 there variations in the hardness of the metal to be cut. 
 On both these accounts the resistance to the cutting 
 action of the tool varies during the traversing motion of 
 the tool. Now, when a place is reached at which the 
 resistance would be greater than elsewhere with the 
 same rate of feed, it is, of course, desirable that the 
 rate of feed should be diminished, so as to reduce the 
 width of shaving cut, and thereby decrease the resistance 
 to cutting. The frictional driving of the feed motion by 
 a belt tends towards this equalisation of cutting effort, 
 because the belt slips slightly, and the more so the 
 greater is the strain put upon it. 
 
 When very exact regularity in the traversing feed is 
 desired, as in screw-cutting, another mechanism is used, 
 which will be described presently. 
 
 9 . The mechanism described in the last paragraph is 
 in many respects clumsy. In order to throw the pinion 
 % and the wheel w out of gear, they have to be slid 
 
116 
 
 CUTTING TOOLS. 
 
 [Chap. VL 
 
 along their respective shafts, and to do this, in the one 
 case at least, an extra rod with a fork is required. It 
 is also to be noticed that u is a worm-wheel, and that 
 this is made to gear with the pinion %. The teeth of 
 both of these must be made oblique in order that they 
 may gear at all, and even when placed at the same angle 
 
 Fig. 33. 
 
 of obliquity in both pinion and wheel, the teeth of the 
 latter cannot be made to fit well both the worm t and the 
 pinion z. 
 
 The design shown in Fig. 33 is a great improvement 
 and simplification of the necessary mechanism. The 
 diagram shows the saddle in plan, with the top slides 
 removed, and with the lathe bed and the rack y broken 
 off. The latter is secured to the front side of the bed, 
 and the pinion x (seen dotted) exerts its driving pressure 
 on the rack much more nearly in a direct line underneath 
 
Chap. VI.] FEED BY FRICTION — CONE CLUTCH. 117 
 
 the cutting point of the tool, where the resistance to mo- 
 tion is generated, than in the former design. 
 
 The worm-wheel w, which gears into the worm t , not 
 shown in the figure, is keyed fast on the shaft which runs 
 to the front of the saddle. Near the front end of this 
 shaft there is formed a cone, which fits into an internal 
 cone cut in the boss of the pinion v 9 and another similar 
 cone stands on the opposite side of this pinion, fitting 
 into a similar recess in the front end of the boss. The 
 pinion and the latter cone both run loose on the shaft, 
 except when, by means of the large nut seen at the end 
 of the shaft, the external and internal cones are tightened 
 and locked together by friction. The friction-cone 
 coupling takes the place of the sliding of the spur-wheels 
 on their feathers, and the tightening or loosening of the 
 cones is effected by a very small rotation of the clamping 
 nut. The putting the self-acting rack feed into and out 
 of gear is by this means made very much more handy 
 and expeditious. The importance of this advantage is 
 not limited to the saving of a little trouble on the part 
 of the turner. If the workman has to turn a parallel 
 length on his work which joins on to a flat surface per- 
 pendicular to the axis of rotation, he must exercise the 
 greatest care in turning the last portion of the parallel 
 run close to the corner, because if he goes the least 
 distance too far he may spoil the flat face, and break his 
 tool as well. With the mode of engagement shown in 
 Fig. 32 there is always a risk of the teeth sticking so 
 hard together when they are in gear that the first effort 
 of the workman will not be sufficient to disengage them. 
 The turner cannot afford to run this risk at the last 
 instant of the parallel cut, and he must, therefore, throw 
 the self-acting feed out of gear when his tool is still at 
 some considerable distance from the corner, and must 
 finish the cut up to the comer by hand feed with the 
 top slide. This process is altogether clumsy and waste- 
 ful of time ; and although the hand feed at the last small 
 fraction of an inch from the corner cannot be dispensed 
 
118 
 
 CUTTING TOOLS. 
 
 [Chap YI. 
 
 with even with the friction-cone engagement, still the 
 latter is so much more certain and rapid in its action 
 that a great deal of time is saved by means of it. 
 
 The pinion v gears into the wheel w 9 seen dotted 
 underneath the saddle, and this is keyed on the same 
 short shaft as the pinion x 9 which engages with the 
 rack y. Another small pinion, sc 1 , is fixed on a bolt with 
 bearings in the saddle, and with its outer end squared 
 for the reception of a crank handle ; x 1 gears into the 
 wheel w 9 and being turned by hand, traverses 1 the slide- 
 rest along the rack. 
 
 On the same shaft that carries the worm-wheel u is 
 also fixed the wheel r. This drives the pinion z 19 which 
 runs loose on the screw-spindle z, except when clamped to 
 it by a friction-cone coupling similar to that already 
 described. In this case the outer cone forms the end 
 of a rod which runs through the screw spindle, this 
 being bored out hollow to admit its passage. The other 
 cone is formed on the end of the hollow screw spindle. 
 The interior rod projects at the front of the saddle, and 
 has its end screwed for the reception of a long nut, rotated 
 by a small hand wheel and cut in the boss of this wheel. 
 By screwing this nut up, which has its flat bearing on the 
 front end of the hollow screw spindle, the spindle, with 
 its cone at its other extremity, is pushed back, while the 
 rod with the opposing cone is drawn forward, so that the 
 pinion z 1 becomes firmly clasped between the two cones. 
 The pinion being thereby put in gear with the screw z, 
 and this working in the nut fastened to the lower side of 
 the surfacing slide, the tool-rest is drawn towards or 
 moved outwards from the axis of rotation of the work 
 by means of the revolution of the worm t 9 driven by the 
 belt at the fast head-stock. 
 
 10. Feed Motion for Screw Cutting. — As already 
 said, a more accurate traversing feed is required for 
 screw cutting. This is obtained by a nut fixed to the 
 underside of the saddle of the slide-rest, and gearing in a 
 long screw, called a “ leading screw,” that runs the whole 
 
Chap. VI.] 
 
 SCREW-CUTTING FEED. 
 
 119 
 
 length of the bed of the lathe. In first-class lathes this 
 screw should be preserved from wear with all possible 
 care. It should, therefore, not form the only self-acting 
 traverse motion, but should be combined with the rack 
 motion described last, and the rack should be used for all 
 work in which great regularity of feed is not necessary. 
 
 In Fig. 32, the leading screw, marked a, is seen in the 
 front elevation A, in the plan B, and in the sections 
 E and F. The nut in which it gears is best seen in E 
 and F. This nut and the casting in which it is held 
 are split in halves, which may be separated so as to 
 stand clear of the screw, and not be in gear, therefore, 
 with it. They slide up and down in a vertically 
 slotted plate, and the engaging or disengaging motion is 
 given to them by two studs which enter the eccentric 
 curved slots in the circular disc seen most plainly in the 
 front view, A. This plate swivels on a central pin, and 
 is moved through the requisite circular arc by a lever 
 bolted to one side of it. 
 
 The nut shown in this figure is of gun-metal set 
 in cast-iron. G-un-metal is still very commonly used 
 for the purpose, but a nut of cast-iron or of malleable 
 cast-iron answers the purpose perfectly if made of extra 
 length. The modern improved custom is also to use only 
 the upper half of the nut. This upper half is all that is 
 required. The use of it alone very much simplifies the 
 mechanism for throwing it into and out of gear, which 
 is reduced to a short hand lever, with an eccentric pin 
 turned on the face of its boss. The upper half-nut also 
 keeps comparatively free of dirt and dust, which readily 
 lodges in the lower half when it is standing clear of the 
 screw. The most important advantage in this improve- 
 ment is, however, that it renders possible the support of 
 very long leading screws by half bearings on the under 
 part of the surface. These bearings are supported on 
 brackets bolted to the lathe bed or legs, and are bored 
 out to a diameter equal to that of the top of the thread 
 of the screw. The complete nut would not permit of 
 
120 
 
 CUTTING TOOLS. 
 
 [Chap. VT. 
 
 these bearings, because thev would interfere with its 
 
 'W * m 
 
 passage along the screw. Leading screws are of a consi- 
 derable weight, and when very long, as in lathes designed 
 for the turning of long lengths of shafting, they bend 
 very considerably if not supported at points intermediate 
 between their ends. 
 
 11 . The best position for the leading screw in the 
 lathe bed is still a matter upon which difference of 
 opinion exists among tool-makers. It is occasionally, 
 but not often, placed at the back of the bed. It is 
 very often put in the hollow space between the back 
 and front slide-surfaces of the bed, as close as is com 
 venient to the front cheek, in order to be protected by 
 the front slide-surface from dirt falling from above, and 
 in order to be as nearly as possible directly under the 
 cutting edge of the tool. It is sometimes said that this 
 position protects the screw from getting dirty. This is a 
 mistaken idea, however, because in consequence of its 
 inaccessible position it seldom or never gets properly 
 cleaned by the lathe man. The sole real advantage of 
 this position is the protection it affords from accidental 
 blows from tools, spanners, &c., falling on it, and from 
 other ill-usage. If the screw is placed in front, as is 
 the commonest and most approved position, it is not 
 infrequently used by thoughtless workmen as a rest 
 in lifting heavy weights from the floor on to the lathe bed, 
 and in this way gets often bent, bashed, and generally 
 ill-treated. The advantage of the front position is its 
 great accessibility for cleaning. It would not appear 
 
 difficult to arrange so that it should be protected by a 
 projecting ledge or shelf cast on the front cheek of the 
 bed. Such a shelf would also be found very useful for 
 laying tools and spanners upon. These are at present 
 usually found in heaps lying all along the bed, whose 
 
 surface it is really important to keep free from 
 
 bruises or defacement of any kind. Besides doing 
 
 injury to the surface of the bed, these heaps of tools 
 are a continual nuisance i*n being swept off and thrown 
 
Chap. YI.] 
 
 SCREW-CUTTING FEED. 
 
 121 
 
 on the floor by the advance of the saddle in its self- 
 acting traverse motion. 
 
 12. There still remains to be mentioned the means 
 by which the leading screw is rotated. The chief 
 object of the leading screw is to traverse the slide- 
 rest and tool in the operation of cutting screw-threads. 
 For each revolution of the piece upon which the thread 
 is being cut. the tool must traverse a distance equal 
 to the desired pitch. If the pitch were equal to that 
 of the leading screw, then evidently the leading screw 
 would need to make one revolution for every revolu- 
 tion of the main spindle. If the pitch were to be half 
 that of the leading screw, then the leading screw must 
 revolve once for every two revolutions of the lathe 
 spindle. Whatever be the thread desired, the ratio 
 between the rate of revolution of the leading screw 
 and that of the lathe spindle must be made the same 
 as that of the pitch of the thread to be cut and the 
 pitch of the leading screw. If this ratio between the 
 speeds of rotation of these two shafts be kept with 
 accuracy constantly the same, the thread will be cut 
 to a uniform pitch, or rather its accuracy will be pro- 
 portional to that of the leading screw. In order to 
 maintain this ratio always the same, the leading screw 
 is driven by the lathe spindle through a train of spur 
 gearing, the teeth of which ought to be cut out accu- 
 rately in a milling machine to a proper shape, and to a 
 uniform pitch. This train of gearing is mounted on a 
 swivelling plate, or, as it is called, the “ radial arm,” 
 which pivots round the screw spindle as a centre. It can 
 be swung round this centre and clamped in any position 
 by means of nuts on a couple of studs projecting from 
 the flat surface against which the swinging-plate bears. 
 The studs pass through two segmental slots made in the 
 plate. This plate is seen in the end view, c, in Fig. 32, 
 and is there marked / 3 . 
 
 Besides the two arched slots, there are two straight 
 slots made in it. In any position in these straight slots 
 
122 CUTTING TOOLS. [Chap. YI. 
 
 may be bolted two studs, the tightening on the plate 
 taking place between collars on the studs and nuts on 
 their screwed ends. On these studs are placed the 
 wheels of the spur gearing. They are called “ change 
 wheels,” and a large number of them is supplied with 
 each lathe. According to the speed desired for the 
 screw spindle, one or other pair of these wheels may 
 be placed on the above studs, and the wheel on the 
 screw itself may also be changed. . Thus different sizes 
 of wheels being in use at different times, it is necessary to 
 have means of mounting them with their centres at 
 corresponding distances apart, and this is done by 
 sliding the studs along the straight slots into suitable 
 positions. The wheel gearing with that on the screw 
 spindle is first set on the stud in the outer slot, and 
 then that which must gear with this is placed suitably 
 in the inner slot. This latter is brought into gear with 
 the pinion on the lathe spindle, either directly by swing- 
 ing the radial arm into such a position that the teeth of 
 the two interlock, or else intermediately through the 
 small wheel Oj, of the same size as that on the lathe 
 spindle, with which it always remains in gear. The 
 object of this intermediate wheel is to reverse the 
 direction of motion of the leading screw, so as to draw 
 the slide-rest from left to right instead of in the opposite 
 direction, which is considered the forward direction for 
 its motion. With the arrangement shown in Fig. 32 
 for this reversal, it is necessary to shift the large radial 
 arm, which is an inconvenient operation. In order to 
 avoid this inconvenience, a small swinging plate with 
 two equal idle wheels gearing with each other is intro- 
 duced. This can be placed either in such a position 
 that the first wheel in the radial arm is driven through 
 one only of these, or so that it is driven through the pair. 
 In the latter position of the plate on which they are 
 mounted one of the pair gears with the pinion on the 
 lathe spindle, while the other gears with the wheel on 
 the radial arm. 
 
Chap. VI.] 
 
 LATHE CENTRES. 
 
 123 
 
 13. Headstock. — Fig. 34 shows the details of the fast 
 headstock of a double-geared lathe. A is a longitudinal 
 vertical section ; c is a sectional plan. The chief part is 
 the spindle, or mandril. The right-hand end of this has 
 an axial hole bored in it, slightly tapered, for the reception 
 of a pointed piece of steel, called the “centre.” This 
 should be carefully fitted to the hole, so as to be perfectly 
 firm in it, and after the lathe has been completely fitted 
 up and put in working trim, the centre must be turned 
 in place. This ensures that it will run absolutely true, 
 with an accuracy that could not be obtained by any other 
 method. Two small holes are made in the work at 
 opposite ends of the axis round which it is desired to 
 turn it. Into these holes are inserted the “ centre ” on 
 the fast headstock, and the similar centre of the loose 
 head-stock shown in d. 
 
 The work is thus suspended between these two points, 
 and is free to rotate about the line joining them. It is 
 carried round with the rotation of the mandril by means 
 to be presently mentioned. The cutting tool turns the 
 work to a surface of revolution, all the centres of whose 
 circular sections lie upon the line joining these centres. 
 If, now, the object is to be turned to the cylindrical 
 shape, or, as it is termed in the workshop, “ parallel ” — 
 referring to the parallelism of the sides of its sections 
 through the axis— the tool must be traversed so as 
 always to stand exactly at the same distance from the 
 line between the “ centres ” in the two head-stocks. If it 
 does not do so, the diameters of the various sections will 
 not all be accurately equal. The slide-rest is guided in 
 its traversing motion by the “bed.” Hence arises the 
 necessity for having the outside edges of the bed, which 
 form the surface that guides the slide-rest, very exactly 
 parallel to the line joining the two centres. This is 
 accomplished, not of course by cutting the bed to suit 
 the centres, but by fitting the tongue-shaped projection 
 on the bottom of the movable head-stock that enters and 
 slides in the groove of the bed, so that the centre on this 
 
124 
 
 CUTTING TOOLS. 
 
 [Cliap. YI. 
 
 head stock will stand above the edges of that groove in a 
 precisely similar position to that occupied by the centre 
 on the fast head-stock. The two centres must stand 
 exactly the same vertical height above the flat upper 
 surface of the bed, and exactly the same horizontal 
 distance measured perpendicularly to the bed from either 
 edge of the inside groove. These inside edges also must 
 be exactly parallel to the outside edges of the bed. Thus 
 this adjustment of the movable head should be the last 
 thing done in the manufacture of the lathe, the turning 
 of the mandril centre being the second last operation, 
 
 14. Centre-point. — It is often stated, in books and 
 elsewhere, that the exact angle of the conical points of 
 the centres is of great importance for accurate work. The 
 writer does not recognise any importance in exactitude 
 in this matter. The best angle certainly varies with the 
 kind and quality of the material turned in the lathe. The 
 considerations which determine that best angle in any 
 special case are the following. The pressure exerted by 
 the cutting tool on the work has two components : one 
 of these is perpendicular to the axis of rotation, and is 
 due to the rotation of the work ; the other is parallel 
 to this axis, and is due to the traversing feed. These 
 pressures are for the most part transmitted to, and borne 
 by, the centres. The bearing surface here is small, and, 
 therefore, the material in the centre hole of the work is 
 gradually crushed proportionally to its degree of soft- 
 ness.- As soon as it is appreciably crushed, the work 
 hangs slightly loose between the centres, and it becomes 
 impossible to turn true work until the centres are 
 tightened up once more. Now this crushing and wear of 
 the material in the centre holes are produced by both the 
 above components of the pressure. The vertical pressure 
 will be better resisted the more acute is the angle of the 
 steel centre, because in that case its sides will be more 
 nearly perpendicular to this component of the whole 
 pressure. But at the same time the material will be less 
 favourably situated to resist the axial pressure component, 
 
Cliap. VI.] 
 
 LATHE CENTRES. 
 
 125 
 
 because the surface will be very oblique to the direction 
 of that thrust, and the conical steel point will penetrate 
 into the metal like a keen-edged wedge. Any change in 
 the angle of the cone is thus advantageous with reference 
 to one component of the pressure, and disadvantageous 
 with regard to the other. The best angle is that with 
 which the combined advantages with reference to ths 
 two are found to be a maximum. It must evidently 
 depend to some extent on the softness of the material 
 being wrought, and also on the ratio between the two 
 components of the pressure. This ratio depends again on 
 the nature of the material, and also still more on the 
 ratio of the amount of traverse-feed given per revolution 
 to the depth of cut. It also depends to a large extent 
 on the form given to the cutting edge of the tool, and the 
 manner in which this is held. As these elements of cal- 
 culation vary greatly in the work of the same lathe, and 
 even during the process of turning one piece of metal, 
 it would be futile to attempt to construct a role for the 
 best angle for the cone of the centre that would be 
 generally true. 
 
 In order to diminish this wear at the centre-points, it 
 is, however, very important to make the centre holes of 
 the same degree of conicity as the centres, so that the 
 two surfaces will bear fairly together. These holes are 
 commonly made by driving in a 1 ‘ centre punch ” with a 
 hammer. This may be a convenient practice for small 
 work, but it is a bad one in any case if the workshop 
 contains facilities for drilling the holes. The centre 
 punch has its point always more obtuse than the farther 
 back portion of its conical surface. The result is that 
 either the punch does not make the hole deep enough, 
 and the lathe centre itself has to complete its formation, 
 whereby too much pressure is brought on its extreme 
 point, or else the centre punch must be ground to an 
 acuter angle than that of the lathe centre, and the surface 
 of the hole it stamps in the work does not conform to 
 that of the lathe centre, and a fair bearing is not obtained. 
 
126 
 
 CUTTING TOOLS. 
 
 [Chap. VI. 
 
 None of tlie pressure should be borne by the extreme 
 point of the centre. In order to avoid this, it is necessary 
 to drill a small hole deeper than the centre-point is in- 
 tended to penetrate. The outer end of this hole is then 
 to be counter-sunk to the right angle to fit the centre. 
 The small drill and the counter-sinking drill may con- 
 veniently form parts of the same tool, which may be 
 used in a hand-brace, or may be inserted in a specially 
 constructed “ centring ” machine. 
 
 The forging or cast-iron piece to be turned has 
 usually an irregular outer surface, and although at 
 some parts a considerable depth of metal has to be 
 removed in order to reduce it to the desired size, at 
 other places there is an extremely small quantity to be 
 taken off. At these places, where the metal in the rough 
 condition is “ scrimp/ 5 it would be impossible to turn off 
 the whole of the outer skin, so as to leave everywhere a 
 clean-cut surface, if the above centre holes were not 
 placed correctly with extreme exactitude. A misplacing 
 of the centre by inch would reduce the diameter to 
 which it would be possible to turn up the scrimp section 
 by ■— inch. With the centre punch it is seldom that the 
 workman can make the hole as exactly as is necessary in 
 the correct position without making a correction in the 
 first hole he makes. He punches the holes as nearly 
 right as he can judge by eye ; he then places the piece in 
 the lathe, and by slowly turning it, and holding apiece of 
 chalk steadily so as just to touch the side farthest from 
 the centre of rotation, he discovers in which direction he 
 must correct his centre hole in order to get a nearly uni- 
 form chalk mark all round. He then removes the piece 
 from the lathe, and alters the hole as required by driving 
 the centre punch to one side or the other. This process 
 evidently must result in a hole that is neither regular in 
 shape nor in the hardness of the metal round about it. 
 The metal on that side to which the punch has been last 
 driven is more compressed than the rest. On account of 
 this difference and the irregularity of shape, the hole will 
 
PLATE VI. 
 
 Fig. C4. -LATHE HEAESTOCKS. 
 
Chap. VI.] 
 
 MANDRIL BEARINGS. 
 
 127 
 
 not wear evenly during the subsequent turning. The 
 position of the centre will gradually shift, and it will be 
 found impossible to produce perfectly true work. 
 
 The centring machine above mentioned finds the true 
 exact centre of the rough surface mechanically. The 
 end of the bar is placed in a concentric chuck with four 
 jaws, and these are screwed down upon it simultaneously. 
 The centring drill, which is made to run exactly true 
 with the jaws of the chuck, is then brought forward, 
 and bores the hole without possibility of error in the 
 exact centre of the largest circle that can be turned on 
 the part gripped in the jaws of the chuck. In the case 
 of bar iron, the ends are the important parts to get 
 well centred. If when these are exactly true other 
 parts of the bar are found to run untruly, they 
 are to be corrected by bending the bar by striking 
 it with a hammer on an anvil or some other solid resist- 
 ing surface. The centring machine is hot, however, 
 applicable to pieces of large size. In the turning of 
 shafting and spindles of all sizes it is a very valuable 
 tool. 
 
 15. The mode of driving the work when it is placed 
 between the centres, and other methods of fastening it in 
 the lathe, will be presently described. 
 
 16. Parallel and Conical Bearings in Headstocks. 
 
 ■ — In Fig. 34 , A and c, it will be seen that the 
 mandril of the fast headstock runs in parallel brass 
 bearings. These brasses are split horizontally, and 
 the upper halves are held down by cast-iron caps, 
 bolted to the standards of the headstock by studs 
 and nuts. As wear occurs, these can be tightened 
 up by screwing down the nuts. The end-pressure due 
 to the traverse feed is partly delivered by a collar on 
 the mandril to the face of the right-hand pair of 
 brasses. The greater portion of this axial pressure 
 is intended, however, to be borne at the left-hand end 
 of the mandril. In the sectional jilan c are seen two 
 horizontally placed pillaret studs attached to the left- 
 
128 
 
 CUTTING TOOLS. 
 
 [Chap. VI. 
 
 hand standard of the head-stock, and both at the level 
 of the mandril centre. Across the extremities of these 
 is bolted a small cast-iron bridge. The mandril thrusts 
 upon this bridge through the intervention of a steel 
 pin that is passed through it and is placed so that 
 its centre-line is a continuation of that of the man- 
 dril. This bearing-pin has its ends screwed, and is 
 clamped by two nuts, one on each side of the bridge. 
 By turning these nuts in either direction, the pin can 
 
 Fig. 35. 
 
 be set forwards or backwards to the right amount, so 
 as just to bring the collar on the front end of the 
 mandril into contact with the brasses without allow- 
 ing any large amount of pressure to be borne by these 
 brasses. 
 
 The mandril is kept from moving forwards axially by 
 two nuts that are placed on a screwed portion of it, 
 immediately behind the left-hand brasses. These nuts 
 are screwed gently against the brasses, and tightly 
 against each other. 
 
 Fig. 35 shows another system that is very commonly 
 adopted for the mandril bearings. Here the bearings 
 are conical and in solid brass bushes. There is here 
 no utility in having a bolted-down cap over the brasses, 
 so that these are simply placed in holes bored to fit them 
 
PLATE VII 
 
 Fig. 38.— FACE LATHE 
 
Chap. VI.] 
 
 CONICAL V. PARALLEL MANDRIL BEARINGS. 129 
 
 in the solid tops of the headstock standards. The wear 
 is “ taken up” by thrusting the cone of the mandril 
 farther into the hollow cone of the brass. In the 
 example shown, the two cones at the two ends are 
 oppositely inclined. It must, therefore, be possible to 
 draw the two cones on the mandril nearer each other 
 as wear proceeds. The one is, therefore, made solid 
 on the mandril, while the other slides loosely on a 
 parallel portion at its back end which is screwed. On 
 this screw there are two nuts, by means of which the 
 sliding cone is pushed forward until the two cones fit 
 closely into their brasses. A small part of the end feed 
 pressure is borne by the conical surface of the front 
 brass, but the main portion of it is borne at the ex- 
 tremity of the mandril by a steel bearing-pin, in a 
 bridge exactly similar to that described in Fig. 34. 
 
 The two cones are not necessarily inclined oppositely 
 as in this example. If, however, they are inclined in 
 the same direction, that at the left-hand end must be 
 made small. Its largest diameter cannot be larger 
 than the smallest diameter of the other cone, in order 
 that the spindle may be passed through the solid brass 
 for this latter and put in place. This results in the 
 screw for the nuts behind the left-hand brass being 
 very small, as also the end of the mandril which rests 
 against the pin for taking the axial thrust. 
 
 The construction (Fig. 35) with conical bearings is 
 considerably less costly than that with parallel split 
 bearings in Fig. 34. Opinion as to the relative merits 
 of the two constructions independently of cost is divided. 
 There is a common idea that the mandril runs truer in 
 conical bearings when equally well finished as the 
 others. The writer has, however, been unable to find 
 any rational ground for this opinion. If the wear at 
 the axial-thrust bearing pin takes place at the same 
 rate as that at the conical bearings, then there may 
 be an advantage in these after wear has taken place. 
 This bearing pin can also be set back from time to 
 j 
 
130 CUTTING TOOLS. [Chap. YI. 
 
 time, as tlie wear ' of the brasses proceeds. But it 
 
 J. 
 
 must not be overlooked that the pressure on the brasses 
 is constantly in one direction, so that the wear of these 
 does not merely make them larger, but results in their 
 becoming oval. To make them true once more, it is 
 necessary to take them out, and either to re-bore them 
 or to bring them back to the circular form by scraping. 
 The same has to be done with parallel bearings, but not 
 so often, because these can be tightened up in the direc- 
 tion of wear by the cap-bolts. Also when re-scraping 
 at last becomes necessary, it is more readily performed 
 on the split than on the solid brasses. 
 
 It is probable that the conical solid bearings are to be 
 preferred, on account of cheapness, for small lathes, while 
 in large lathes the parallel split brasses are decidedly the 
 better. 
 
 17. Double Gear. — Upon the mandril in the fast head- 
 jtock is mounted a stepped cone pulley. A belt from a 
 similar stepped cone pulley on the “ counter-shaft ” over- 
 head drives this. The overhead pulley has its large 
 diameter directly above the small diameter, and its small 
 diameter directly over the large end of the lathe pulley. 
 The belt may be put upon any pair of the “ steps.” When 
 it runs from a large size above to a small size on the 
 lathe, the lathe pulley runs faster than the counter-shaft, 
 and vice, versa. Thus for one and the same speed of 
 the counter-shaft as many speeds may be obtained for 
 the lathe pulley as it has “steps.” In Fig. 34 there 
 are five speeds, and in Fig. 35 there are four. If this 
 variation of speed be considered sufficient for the pur- 
 poses to which the lathe is to be applied, the pulley is 
 keyed to the mandril, and drives it directly. In this 
 case there are no other wheels about the headstock, and 
 the lathe is said to be “ single geared .” 
 
 In the lathe shown in Fig. 34 this number of varia- 
 tions of speed is doubled by the addition of extra toothed 
 gearing, and the lathe is said to be “ double geared .” In 
 this case the cone pulley is not ke^' cd to the spindle, on 
 
Chap. VI.] 
 
 DOUBLE-GEARED HEADSTOCK. 
 
 131 
 
 which, it runs loosely. On the small end of the pulley is 
 keyed a spur pinion, marked e in the sectional plan C 
 and vertical section A. In plain bearings in the side of 
 the headstock is placed a horizontal bolt, upon which 
 revolves a hollow cast-iron shaft, having keyed to its ends 
 the spur wheel f and the spur pinion g. This bolt can 
 be' shifted in position so as to stand nearer or farther 
 away from the cone pulley. When placed in its nearer 
 position, the teeth of f engage with those of e, and the 
 teeth of g engage with those of the spur wheel h, which 
 is keyed on the mandril on which the cone pulley revolves 
 loosely. The cone pulley thus drives the wheel f at a 
 slower rate than itself in the ratio of the number of 
 teeth in e to that in which ratio is in the example 
 shown • and this being keyed on the same shaft as < 7 , 
 drives h and the lathe mandril at a still slower rate in the 
 ratio of the number of teeth in g to that in h, or in this 
 example in the same ratio again -f-^. Thus the mandril 
 runs slower than the cone pulley in the ratio foxfi = T 17. 
 With the belt on the five different speeds of the cone, five 
 rates of slow revolution of the mandril are obtained. 
 
 When the bolt, or back shaft, as it is termed, on which 
 are fixed f and g is moved to its position farther away 
 from the cone pulley, these fall out of gear with the 
 pinion e and the wheel h , so that the rotation of the 
 pulley has no effect in moving f and g does not interfere 
 in any way with the motion of h ; h can now be fastened 
 to the cone pulley by means of the belt seen in figure A. 
 The pulley then drives h and the mandril at the rate 
 at which it runs itself. Thus, by again shifting the 
 belt, five new speeds are obtained different from the 
 previous five. The largest step on the cone has a dia- 
 meter of about 16 J inches, and the smallest one of 4f 
 inches. As the sizes of the cone on the counter-shaft 
 overhead are the same, the fastest of these speeds is 
 
 faster than the slowest in the ratio = about 13. 
 
 If the fastest of these speeds be combined with the 
 double gear, which reduces the speed in the ratio T17, 
 
132 
 
 CUTTING TOOLS. 
 
 [Chap. VI. 
 
 calculated above, the resulting speed of the mandril will 
 be 13 x *117 = about 1J times the slowest speed obtain- 
 able in single gear. Thus the two sets of speeds overlap 
 each other, and the dimensions of the example are so 
 arranged as to give two different methods of approximat- 
 ing to any desired medium speed. This is not entirely 
 without utility. The medium speed in single gear causes 
 less frictional waste of power, because of the spur gear- 
 ing not being in action. On the other hand, in the use 
 of the double gear for the medium speed, the belt passes 
 over the surface of the larger end of the lathe pulley, and 
 gets a better hold of it. At the same time it passes over 
 the smaller end of the driving pulley overhead, but here 
 the belt is somewhat tighter than on the lower pulley, in 
 consequence of its own weight. This difference in tight- 
 ness is slight, but a very small increase in tightness is 
 sufficient to enable a considerably greater driving pull to 
 be transmitted by the friction between pulley and belt. 
 
 The actual speeds of the lathe mandril in the example 
 shown in Fig. 34, when the counter-shaft runs at forty 
 revolutions per minute, would be approximately : 
 
 In single gear, 11, 22J, 40, 71, and 142J turns per 
 minute. 
 
 In double gear, 1-J, 2J, 4^, 8|, and 16 J turns per 
 minute. 
 
 18. The back shaft on which f and g (Fig. 34, c) 
 are mounted is approached and receded from the cone 
 pulley by having its ends turned eccentrically. By 
 rotating the eccentric ends through half a turn in 
 their fixed cylinclric bearings, the centre line of the 
 shaft is shifted, since that of the eccentric ends main- 
 tains its position unaltered. These ends are shown 
 in c. It will be observed that while the left-hand 
 end is solid in one piece with the shaft, the right- 
 hand end is, on the contrary, a separate loose piece. 
 This is necessary because the ends are made larger 
 in size than the main body of the shaft, while this 
 has to be passed through the ends of the hollow shaft, 
 
Chap. VI.] MOVABLE POPPET-HEAD. 133 
 
 into which it is made to fit. It would be impossible to 
 put the pieces together if both ends were larger than the 
 intermediate part fitting the hollow shaft. 
 
 19. Loose Headstock. — In d we have a vertical 
 longitudinal section through the movable headstock, or 
 poppet-head. This can be shifted along the bed of the 
 lathe into any position, so that longer or shorter pieces 
 may be supported between the centres. The bolt, passing 
 downwards through its centre, clamps it to the bed in 
 any desired position by means of a small cross-bridge 
 spanning the under side of the shears in the hollow space 
 between the cheeks of the bed. 
 
 After clamping in this way, a further longitudinal 
 motion can be given to the centre-point by means of the 
 screw which is seen in the diagram to be attached to the 
 small hand-wheel at the right-hand extremity of the 
 poppet-head. The object of this wheel is to turn the 
 screw. The screw is prevented from longitudinal motion 
 by collars — of which one is formed by the boss of the 
 hand-wheel keyed on it — on each side of a plate screwed 
 fast to the end of the headstock. The steel centre is 
 fitted in a tapered hole in the end of a cylinder, which 
 may slide out and in in the interior of the head which is 
 bored to fit it. A longitudinal groove, or key slot, is cut 
 in this cylinder, and a feather in the casting fits in this 
 slot and prevents the cylinder from turning. At the in- 
 side end of the sliding cylinder is a nut, into which the 
 screw enters. Since the nut cannot turn, it must advance 
 along the screw when this latter rotates, and thus the 
 point is moved out and in. 
 
 20. As before explained, for parallel turning it is 
 very important that the centre in this movable poppet- 
 head should stand in exactly the same position relatively 
 to the edges of the bed as does the centre in the fast 
 headstock. If it stands a little to one side of this 
 correct position, then the ordinary traversing motion 
 of the slide-rest results in a smaller section being 
 turned at the one end of the traverse than at the 
 
134 
 
 CUTTING TOOLS. 
 
 rClmp. YI. 
 
 other, the difference in the diameters of the two end 
 sections being twice the difference between the positions 
 of the two centres, measured relatively to the bed. 
 Advantage is frequently taken of this fact for slightly 
 taper turning. For this object the movable poppet- 
 head is purposely put backward or forward out of its 
 true position by an amount corresponding to the degree 
 of taper required. Some poppet-heads are for this 
 purpose made of two parts, the lower being a flat 
 plate on which the upper part may slide to a small 
 extent. It is made to slide the desired amount by 
 set screws and is then clamped in position. This 
 construction is strongly disapproved by many good 
 makers of tools because of the risk of the poppet being 
 carelessly left set to one side, when work may be spoilt by 
 its being forgotten to set it back to its central position 
 for parallel turning. It is also a troublesome operation 
 to set it again in this central position with the needful 
 accuracy. 
 
 21. Modes of Driving and Chucking Work. — The 
 front end of the sjundle in the fast-head is screwed for 
 the reception of various “ face-plates ” “chucks” and 
 “ drivers.” 
 
 In Fig. 36 a shows a “driver” of the kind most 
 
 O 
 
 commonly used. It is simply a small solid plate screwed 
 on the mandril, and having firmly fixed in its face, near 
 
 the edge, a strong projecting pin. 
 a The figure b represents what is 
 in technical language called a 
 “ carrier.” This is a cross-piece, to 
 be fixed on the bar or other work 
 to be turned. It has through it a 
 hole of oval, or rather, egg-shaped, 
 form. The bar is put through this 
 
 hole, and is screwed down tight into the smaller end of this 
 
 hole. In consequence of the tapering egg-shaped form of 
 the hole, one size of carrier will admit, and hold fast, bars 
 
 whose sizes differ considerably. The size of the bar being 
 
Cliap. VI.] 
 
 DRIVERS AND CARRIERS. 
 
 135 
 
 greater than that of the circle to which the small end 
 of the hole is formed, it rests on two points at the 
 sides of the hole. The end of the screw comes on a 
 third part of the circumference of the bar, which is thus 
 securely gripped between these three points. This 
 carrier being placed at the extremity of the work, where 
 it rests on the centre in the mandril, one or other end of 
 the carrier catches on the projecting bolt of the driver, 
 and by this means the rotation of the mandril is commu- 
 nicated to the work. The part of the work on which the 
 carrier is fixed is ordinarily in the rough condition and, 
 owing to the inequalities of the surface, a large amount 
 of power can be transmitted by this fastening. When a 
 similar carrier is used ujion work that has already been 
 turned, the driving effort is exerted wholly by means of 
 friction, and on this account the thick end of the carrier, 
 which forms the nut for the clamping screw, must be 
 made longer than the usual length of a nut of corres- 
 ponding diameter, in order that the bolt may be screwed 
 down very fast without risk of stripping the threads. 
 The carrier should either be forged or made of malleable 
 cast-iron. 
 
 Sometimes the driver has two projecting prongs on 
 opposite sides of its disc. If- these are fixed immovably, 
 it will be found that the opposite ends of the carrier 
 seldom both catch on the prongs because of the two ends 
 of the carrier not being alike. A bearing may be got on 
 the pin at the small end of the carrier,- so that this as 
 well as the opposite pin should share the driving work, 
 by slipping over it one or more short ferrules as packing 
 between it and the carrier end. A number of pieces of 
 ferrule of different thicknesses may be kept by the lathe 
 ready to hand. 
 
 In Clements’s driver the two prongs, are upon a front 
 plate, which may slide a short distance on the face of the 
 plate screwed on the mandril. The prongs may thus be 
 thrown to one side by an amount just necessary to let 
 them both catch equally on the work, and in this position 
 
136 CUTTING TOOLS. [Chap.VX. 
 
 the front plate bearing these prongs is clamped by a 
 couple of studs and nuts to the plate behind it. These 
 drivers are a good deal used, but they do not appear to 
 possess any superiority of merit that compensates for 
 their extra complication and cost. Instead of a “ driver” 
 proper, a face-plate, with a bolt fixed in one of its holes so 
 as to project from the face, may be used and does equally 
 well. 
 
 22 . Driving by Face-Plates. — The above carriers 
 are made of various sizes, but never of such a size 
 as to admit of their application to work of more than 
 three or four inches in diameter. When the piece is 
 larger than this, and is placed between the centre-points, 
 it is usually driven by bolts, fastened so as to project 
 from a face-plate such as that shown in Fig. 32. Such 
 large pieces of work have ordinarily some projecting 
 parts, either internal or external, which serve as abut- 
 ments against which these bolts may thrust. 
 
 When the work has no great length in proportion to 
 its diameter, it is not usually supported between the 
 centres, but is secured rigidly to the mandril by either .a 
 face-plate ora“ dog-chuck.” The face-plate is simply a 
 large circular disc screwed on the end of the mandril, 
 and with a large number of square holes and rectangular 
 slots cast in it. Through a convenient number of these 
 holes are passed bolts, by which, with the help of clamp- 
 ing-plates, the work is firmly secured. This mode of 
 securing it is especially convenient when a central hole 
 has to be bored out in the lathe, and when flat surfaces 
 perpendicular to the axis of rotation and of greater radial 
 width than can be reached by the projecting length of 
 the tool-shank, have to be cut. The movable headstock 
 is slid back so as to be out of the way, and so as to allow 
 the slide-rest to be brought near the centre of the bed. 
 
 When two such parallel surfaces have to be turned, 
 the piece is bolted to the face-plate, in the first place, in 
 its rough condition, and as nearly as possible in the 
 correct position. The one face is then turned. This 
 
Chap. VI.] 
 
 FACE-PLATES. 
 
 137 
 
 flattened surface is next bolted to the face-plate ; and if 
 this latter be truly perpendicular to the mandril, the 
 second face may now be turned, with the certainty of 
 getting it accurately parallel to the first provided it is 
 made flat — that is, neither hollow nor round. This latter 
 result is attained if the slide along which the tool-rest 
 travels be accurately perpendicular to the mandril. It 
 is evidently of the greatest importance to have the 
 surface of the face-plate to run perfectly true. To 
 ensure this it is in the first place necessary that it 
 should screw on the end of the mandril quite tightly. 
 The external and internal screws of the joint must, 
 therefore, be made very carefully to fit each other. In 
 the manufacture of the lathe after this fit has been 
 attended to, the face-plate should be screwed in place, 
 the lathe driven as it will be in after use, and the face- 
 plate turned up in the lathe itself. This finishing of the 
 face-plate in place is the only method by which it can be 
 got true. In the course of time and use the thread of 
 the screw may get slightly bent or otherwise injured, 
 the fit between the face-plate boss and the mandril collar 
 may get worn, and the metal of the plate may warp 
 slightly. To re-true the face-plate, it should, in the 
 first place, be bolted with its face against the face of 
 another face-plate, either on the same or another lathe 
 that has been ascertained to be true, and the back face 
 of the boss should be trued up. The front face of the 
 mandril collar should then be re-turned, and finally the 
 face-plate screwed against it in the ordinary position and 
 re-turned. 
 
 Two or three face-plates of different sizes should be 
 furnished with every lathe that is intended to do a 
 variety of work. For very large lathes they are the 
 almost exclusively employed means of fixing the work. 
 Those of these large lathes that are used chiefly for plane 
 surfaces are called “ face-lathes/’ and have generally only 
 one large face-plate, which is kept permanently fixed to 
 the mandril. Such a large face-plate may be seen in 
 
138 
 
 CUTTING TOOLS. 
 
 [Chap. YI. 
 
 Fig. 38 (Plate VII.), which, represents one of 7 feet 
 6 inches in diameter. 
 
 23. Driving "by Jaw-Chucks. — A third way of fast- 
 ening the work to the mandril is by means of “ dog- 
 chucks/ 5 These are used for the same sort of work 
 as are face-plates, but are only suitable for moderately 
 small sizes. 
 
 The commonest form is the 4-jaw chuck, an example 
 of which is shown in Fig. 34. There are four radial 
 screws in the face-plate, marked 7c', and seen in the 
 figs. A and B. Hear the edge of the plate the shafts 
 of these screws are squared down, so that they may be 
 turned by the application of a box key. They are pre- 
 vented by a collar from moving radially, and each passes 
 through a large nut that may slide to and fro in a radial 
 slot, but is prevented by the sides of this slot from 
 turning. The rotation of the screw thus forces the 
 nut inward towards the centre, or vice versa. The 
 nut forms part of a piece that projects from the sur- 
 face of the plate in the form of a miniature staircase 
 of two, three, or more steps. There being four of these 
 on two rectangular diameters of the plate, the work is 
 gripped between the four of one series. There are also 
 sometimes one or two steps on the part of the jaw 
 farthest from the centre, in order that the work may 
 be grasped by an internal surface. The cylindrical 
 faces of the steps directed towards the centre, as also 
 the outer cylindrical faces, are ribbed, so as to grip more 
 securely on the work. These pieces are called the 
 “dogs,” or “jaws.” Each may be screwed in inde- 
 pendently. The ribbed surfaces should be either faced 
 with steel, or at any rate case-hardened, because the 
 gripping pressure applied through them rapidly wears 
 the ribs down, after which they cannot be depended 
 on to hold securely. The gripping pressure is applied 
 only, and not maintained, by means of the screws. 
 From the back of each nut a stud stands out behind 
 the face-plate. This stud being screwed, a strong 
 
Chap. VI.] 
 
 JAW-CHUCKS. 
 
 139 
 
 washer and a nut serve to clamp the dog in any 
 position on the plate to which it may be brought by 
 the radial screw. 
 
 Similar chucks are made occasionally with two dogs 
 only, and more frequently with three. If the cutting 
 power proposed to be applied can be transmitted by the 
 frictional grip of three dogs, this arrangement is more 
 scientific, as well as cheaper, than that with four, three 
 being all that are needed in order to keep the work 
 centrally in place. 
 
 These dog-chucks are, of all methods of fastening the 
 piece to be turned, the most unsatisfactory. There is a 
 continual tendency to drag the piece out of the jaws 
 forwards. The cutting pressure of the tool does not 
 only tend to hinder rotation. Its moment to hinder the 
 rotation of the mandril is equal to the product of the 
 force by half the diameter of the section being turned. 
 But the force also exerts another moment, tending to lift 
 the right-hand end of the work bodily up — that is, tend- 
 ing to rotate it round a horizontal axis passing along the 
 face of the jaw-chuck. This moment is equal to the 
 cutting force multiplied by the horizontal distance by 
 which the point of the tool stands from the jaws. At 
 each instant its effort is exerted to tear the work out of 
 the jaws at the lowest point, and to push it farther in at 
 the topmost part of the chuck. Each jaw comes alter- 
 nately to the top and bottom, and the above action results 
 in each part of the work being pushed in and pulled out 
 with very considerable force once per revolution. The 
 consequence is that the grip which the jaws have of the 
 metal is gradually loosened, the work may shift in posi- 
 tion, and not unfrequently the turner finds that it has 
 done so in the middle of his operations, so that the latter 
 half of the parts he has turned are not concentric or co- 
 axial with the former half. ITe has then to loosen his 
 chuck, re-set the piece, tighten up the jaws once more, 
 and go over the whole work a second time in order to 
 true it — if, indeed, he does not find that he has already 
 
140 CUTTING TOOLS. [Chap. VI. 
 
 cut so much material off as to leave him nothing, or in- 
 sufficient to enable him to make this correction. 
 
 These jaw-chucks have one other defect, in that it is 
 difficult to get the face of the work to lie close against 
 the flat face of the jaw. The flat faces of all the three or 
 the four jaws are turned together, so as to form one 
 accurately plane surface perpendicular to the axis of 
 rotation upon which it is intended that the work should 
 be in close contact. But when the jaws are tightened on 
 the work, any little irregularity on the cylindrical surface 
 that is thus grasped leads to one or both sides being 
 
 slightly thrust for- 
 ward, so that the 
 two faces which are 
 desired to be together 
 are separated by a 
 small space. Thus 
 two accurately paral- 
 lel faces cannot be 
 turned in a chuck of 
 this sort as they can 
 on the face-plate as 
 explained above. 
 
 The construction 
 shown in Fig. 37 has 
 been designed to 
 rectify these faults 
 as far as possible. 
 The ribs on the jaw 
 are slightly pointed 
 towards the face of the plate, being shaped like the 
 teeth of a saw, so as to hold the work better in the 
 direction most needed. The jaw is made in two parts, 
 the one with a nut and clamping stud and shaped 
 like the common jaw, the second hinged to this and 
 forming the gripping face, or Actual jaw. This second 
 part is wholly made of steel, and being of small size, 
 is inexpensive and can easily be renewed if the teeth 
 
 Fig. 37. 
 
Cliap. VI.] 
 
 CONCENTRIC JAW-CHUCKS. 
 
 141 
 
 become broken or worn away. Behind the foot of this 
 smaller piece there is inserted in a recess drilled in 
 the larger one a small block of india-rubber or a small 
 spiral spring. This throws the hinged part into the 
 oblique position shown in the diagram, so long as there 
 is no pressure applied to the toothed face. The upper 
 back edge of this part rests against the back of the 
 recess in the hinge casting, and the jaw is thus pre- 
 vented from being thrown out by the spring to any 
 greater inclination than that shown in the figure. 
 When the jaw is screwed down on the cylindrical sur- 
 face of the object to be gripped, the spring is crushed 
 back, and the jaw recedes to a position perpendicular to 
 the plate. In this backward motion all the teeth have a 
 small component movement towards the plate. Since 
 they are at the same time always bearing harder and 
 harder on the work, and are becoming to a minute 
 degree pressed into and embedded in its surface, they 
 effectually prevent any risk of the work separating 
 farther apart from the plane face than it has been set, 
 and, on the contrary, draw it down close on that surface 
 with very considerable force. 
 
 24. Concentric Jaw- Chucks. — The jaw-chucks of 
 which a description has been given in the last para- 
 graph, all have their jaws, or dogs, moved independently 
 by separate screws. The jaws themselves, therefore, 
 are of no use for the purpose of centring objects 
 in the lathe. This must be done by trial and error, 
 the error being discovered by running the lathe with 
 the work clamped in the chuck and marking it with 
 chalk to show the high places, and the correction 
 being applied by screwing one jaw outwards and 
 the opposite one inwards to the same extent. This 
 process occupies some time ; and if the lathe is used for 
 odd jobs, each of which takes only a short time to finish, 
 or for work which has to be frequently taken out of the 
 chuck and re-set in it — as, for example, in turning pins 
 which are to be exactly fitted in the lathe to the holes in 
 
142 
 
 CUTTING TOOLS. 
 
 [Chap. VL 
 
 which they are to he inserted — there is expended in this 
 centring operation a considerable and wasteful proportion 
 of the whole time spent in the work. In such circum- 
 stances a chuck in which all the jaws are made mechani- 
 cally to move simultaneously out and in from and to the 
 centre by precisely equal amounts is of very great ad- 
 vantage. Such a chuck is called a concentric jaw-chuck. 
 If the jaws are once placed so as all to lie accurately in 
 one cylindric surface whose axis coincides with that of 
 the lathe spindle and of the chuck, then the jaws may be 
 moved together to any other distance from the centre, 
 and they will still be accurately in one and the same 
 cylindric surface concentric with the mandril. The jaws 
 themselves, therefore, will bring any object clasped in 
 them to coincide axially with the mandril. The work is 
 thus mechanically centred. 
 
 There have been invented many forms of chucks of 
 this description. The different jaws have to be con- 
 nected by one or other kind of gearing, and this com- 
 plication in the construction makes the chuck not only 
 expensive in first cost, but also very apt to get broken 
 if not used with special care. These disadvantages, 
 however, do not by any means counterbalance the great 
 saving in time attained by their use in the class of work 
 above mentioned. But they are not suitable for large 
 lathes, and, therefore, have never been made except of a 
 small size. 
 
 The pattern that is at present the most favoured — - 
 and will continue to be so until something new and 
 simpler has been invented — is Weston’s American 
 Scroll Chuck. This consists of four plates, which are 
 put together so that three of them are immovably 
 attached to each other and form one rigid piece, in 
 which there is a deep circular groove. In this groove 
 the fourth plate fits, and can revolve. This revolving 
 plate has a square-thread spiral cut on its face. In 
 front of this spiral there are cut three radial grooves 
 in the face of the chuck, and in these slide out and in 
 
Chap. YI.J 
 
 LATHE-BEDS. 
 
 143 
 
 three stepped jaws. These are prevented from falling 
 forwards out of the grooves by feathers running radially 
 along the edges of the grooves. The back or interior 
 surface of each jaw has formed on it several square 
 teeth which tit into the spaces between the successive 
 turns of the thread of the spiral. When the spiral 
 plate is revolved without any corresponding rotation 
 of the jaw-plate, the jaws, being in gear with the spiral 
 through their teeth, are compelled to move radially, and 
 all move by the same amount. 
 
 The jaws of this and the other previously mentioned 
 chucks are too large to admit of their coming so close 
 together as to grip pieces of very small diameter. A 
 special chuck, called a drill chuck, is required for this 
 purpose. It is a concentric chuck, and does not differ 
 in principle from that last described. Its jaws have 
 very narrow faces, and the whole instrument is of small 
 size. It is suitable for use in small lathes. 
 
 25. Function of Lathe Bed. — The bed of a lathe 
 has two functions. In the first place, it bears the 
 slide-rest and the two headstocks. The cutting thrust 
 on the tool is delivered to the bed by the bottom 
 plate of the slide-rest, and is transmitted by it hori- 
 zontally to the points at which the headstocks stand. 
 Between these two latter points the bed acts as a 
 beam, loaded at a point intermediate between its 
 supports. The dimensions of the section, of which the 
 depth is most important, need not be calculated with 
 reference to strength. The depth chosen is always 
 enormously in excess of that needed to prevent breakage 
 from the tool-thrust. Considerations of stiffness rather 
 than of strength ought to regulate this depth. For 
 accurate work it is evidently necessary that the bed 
 should not yield in the minutest perceptible degree to 
 this force. If it did, the position of the tool would sink, 
 and regularity of the diameter cut would not be main- 
 tained. The fact that the piece of work being turned 
 is nearly always pliable to a greater degree than the bed, 
 
144 CUTTING TOOLS. [CJiap. VI. 
 
 and that, therefore, inaccuracy is more to be feared from 
 the spring of the work than from the spring of the bed, 
 is no good reason for making the bed weak enough to 
 have appreciable spring. The spring of the work is 
 unavoidable ; it occurs as a necessity of the shape 
 required to be given to the work ; that of the bed 
 is avoidable, and there is the more reason to avoid it 
 because the other source of error is inevitable. 
 
 The other function of the bed is to guide the tool- 
 rest in its traversing motion. It is necessary that this 
 guidance should keep the motion of the saddle very 
 exactly in one straight line throughout its whole 
 length, and that this line should be accurately parallel 
 to the line between the steel centres. It is of the 
 greatest importance, therefore, to have the upper 
 surface of the bed quite plane, and the edges per- 
 fectly straight. These are . not only planed very 
 carefully in a planing machine, but are also scraped 
 up true throughout their whole length. The vertical 
 edge is necessarily very limited in depth and there- 
 fore does not present a large wearing surface. It is 
 well worth considering whether this edge may not 
 with advantage be made considerably deeper than is 
 at present usual. The under oblique surface of the 
 dovetail projections also partake in the work of guid- 
 ance. Their straightness and exact flatness require 
 to be attended to as carefully as those of the other 
 finished surfaces of the bed. If the thickness of this 
 dovetail be not exactly uniform from end to end of 
 the bed, or if the angle which its lower surface forms 
 with the upper horizontal surface be not maintained 
 precisely regular throughout the same length, the 
 result is that the dovetailed groove of the saddle that 
 spans the groove and should clasp it with the proper 
 degree of tightness, will fit tightly at some places and 
 loosely at others. If this is so, the straightness of the 
 guidance is inevitably lost, and it is thus evident that 
 the careful formation of the under surfaces of the dove 
 
Cliap. YI.] 
 
 GAP-LATHES. 
 
 145 
 
 tail edges of the bed is as important as that of any other 
 part. 
 
 28. Size of Lathe; Gap-Lathes. — The size of an 
 ordinary lathe is stated by the vertical height of the 
 steel centre-points above the flat upper surface of the 
 bed. If this surface be continued underneath the 
 work, it is evident that the diameter of the work 
 cannot be greater than double this height. Indeed, 
 no portion of the work underneath which it may be 
 necessary to bring the saddle of the slide-rest can be 
 of so great diameter. In this case the largest possible 
 diameter is less than the above by twice the thickness of 
 the plate forming the saddle. This does not imply, 
 however, an impossibility of operating upon parts of 
 the work of greater diameter than this, because the 
 cutting-edge of the tool may be made to project to 
 either the right or left of the rest, so that it may 
 cut on a part that does not lie over the saddle. The 
 tool being held so that the saddle does not interfere, the 
 size of the object turned may be twice the height of the 
 centres above the slide-surface of the bed; or it may be 
 even greater than this, if part of the bed be cut away so 
 as to allow the work to come below its upper line. 
 
 Lathes whose beds are shaped in this way are called 
 “gap ’’-lathes, because there is an opening or gap between 
 the part of the bed on which the fast headstock stands 
 and that on which the slide-rest moves. 
 
 Between these two parts the bed is bent downwards 
 in the shape of a crank. The bed is continued of its 
 full depth throughout this cranked portion, so that the 
 whole retains nearly all the stiffness it would have if it 
 were not so cranked. The gap is 6 to 16 or 18 inches 
 wide, according to the size of the lathe. The length of the 
 large part of the work is limited by the width of the gap, 
 and its size may be twice the height to the centre from 
 the bottom of the gap. When the gap is not required, 
 it is filled up by a bridge-piece fitted carefully to the 
 planed edges of the gap, and bolted down securely to the 
 K 
 
146 
 
 CUTTING TOOLS. 
 
 [Chap. VI. 
 
 under part o£ the bed. If the bridge-piece is made to 
 fit very exactly, and is properly fastened, it strengthens 
 the bed so that it may be as stiff as if the gap did not 
 exist ; but this will not be effected if there is the minutest 
 degree of slackness in the fitting of the piece. 
 
 27. Break-Lathe. — In this last construction the con- 
 tinuity of the bed is maintained from end to end, 
 although the straightness of its top surface is sacri- 
 ficed to the gap. When the size of the work is to 
 be so much greater than the height of the centres 
 that the depth of the gap would be inconvenient, the 
 bed is made in two pieces, each of which is bolted on 
 a shallow base-plate on the ground. The one part is 
 fixed permanently at one end of this lower plate, and 
 carries the fast head stock ; the other may be shifted 
 nearer or farther from the first, so as to leave the space 
 between them narrower or wider. This construction is 
 referred to by the name of “break-lathe.” On the second 
 right-hand portion of the bed stands a movable poppet- 
 head and a slide-rest, to which can be given a self-acting 
 traverse feed motion by means of a longitudinal shaft 
 near the level of the ground. The shaft is slotted through- 
 out its length for the reception of a feather upon a 
 pinion which slides along it, and forms the connection 
 between it and the gear, actuating the feed motion. By 
 means of this gear, not only a traversing, but also a sur- 
 facing, feed may be obtained. 
 
 28. Face-Lathe. — In what are termed “face-lathes” 
 the work operated on has only a small axial length, so 
 that the length of traverse feed required is not more 
 than can be given by the motion of the upper upon 
 the lower part of the slide-rest itself. At the same time, 
 a large extent of surfacing motion is required to be given 
 to the tool. In these lathes, therefore, the bed for tra- 
 versing the slide-rest upon is discarded altogether. Fig. 
 38 (Plate VII.) shows such a lathe. A very large face- 
 plate, in the example illustrated 90 inches in diameter, is 
 mounted on the mandril, about 8 inches in diameter, of 
 
Chap. YI.] 
 
 FACE- LATHES. 
 
 147 
 
 a correspondingly large headstock. This is secured by 
 four large bolts to a strong base-plate of about 8J inches 
 deep. This plate extends no farther than the front of 
 the headstock. In front of this lies a second base-plate, 
 which is marked p in the diagrams A, B, and c. It has 
 only a small breadth in the direction of the axis of the 
 mandril, but stretches parallel to the face-plate a distance 
 of 10J feet to one side of the centre. In the direction 
 of its length it has three pairs of undercut grooves 
 planed in its surface, which receive T-headed bolts by 
 which to fix in any desired position the bottom plate of 
 the slide-rest. The slide-rest is a high massive pile of 
 five pieces, movable one over the other. The lowest of 
 these stretches over two of the three pairs of grooves. 
 It may stand over the space between the second and 
 third pairs of grooves, or may be shifted into the space 
 nearer the face-plate between the first and second pairs. 
 It is moved along these grooves to any desired distance 
 from the centre of the face-plate by hand with the assis- 
 tance of a crow-bar. This lowest plate is marked q x , and 
 on its upper surface is a pair of grooves at right angles 
 to the direction in which it is movable. In these lie the 
 T-heads of bolts which fasten the second piece q 2 to q L . 
 This piece is moved by hand along these grooves to any 
 desired distance from the face-plate, and clamped in that 
 position by the bolts. It has a height of 16 inches. Its 
 upper surface is a horizontal circular table, on which the 
 third plate q 3 rests. In q s are circular grooves which 
 allow it to be slewed round so that the slides above q 3 
 may run at any specified angle to the surface of the face- 
 plate. The upper part of q 3 is a long dovetailed slide, in 
 which the screw r v gives a surface feed motion to the 
 plate r that lies above q 3 . This plate r has a similar, but 
 much shorter, slide at right angles to that on q 3 , and a 
 screw having bearings in r gives traversing motion to the 
 uppermost plate s , upon which is clamped the tool in the 
 usual manner. The two upper slides may be worked by 
 hand, or may be made self-acting by a ratchet-wheel and 
 
148 
 
 CUTTING TOOLS. 
 
 [Chap. VI. 
 
 pawl. The pawl is oscillated by a chain which hangs 
 from a short; lever on an overhead rocking shaft. The 
 shaft extends along the roof of the workshop to over the 
 hindmost end of the headstock. Here a small disc 
 crank, with its crank pin in a radial slot, so that it may 
 have different throws according to its position in the 
 slot, drags downwards once per revolution of the man- 
 dril the end of a chain attached at its upper end to 
 a second lever on the rocking shaft. 
 
 In the surfacing bed-plate p the space between the 
 two further pairs of grooves is filled up by a strong web 
 of iron. That, however, between the first and second 
 pairs, and partly directly underneath the face-plate, is left 
 open. Underneath this open space in the base-plate is 
 dug in the foundation a trench, in the form of a quarter 
 circle. This space is left open, in order to admit of flat 
 objects of great diameter, such as large fly-wheels, being 
 turned. Pieces of twenty feet diameter can be taken in 
 the lathe illustrated. 
 
 The two baseplates of this lathe ought to be placed 
 upon a solidly-built foundation of concrete, and bolted 
 down firmly to it, in order that both may at first be 
 placed accurately level, and thus have the plane of the 
 second parallel to the axis of the mandril, and that they 
 should maintain this relative position permanently. If 
 the adjustment of the one plate to the other be disturbed 
 by the sinking of part of the foundation, then the tra- 
 versing slide remains no longer perpendicular to the face- 
 plate, and it becomes a very troublesome job to turn a sur- 
 face truly cylindrical. 
 
 29. Treble Gear. — This lathe is “treble-geared”: 
 that is, with the belt running upon any given step 
 of the cone pulley, the face plate may be run at each 
 of three different speeds, according to the arrange- 
 ment of the spur-wheels and pinions. As there are 
 five steps on the cone, there are, therefore, fifteen 
 speeds at which the lathe may be driven. The cone 
 runs loosely on the mandril, and at its large end 
 
Cliap. YI.] 
 
 TREBLE GEAR. 
 
 149 
 
 there is a spur-wheel, which is keyed on the mandril. 
 The pinion on the hack shaft being slid along this shaft 
 so as to be out of gear with this wheel, the wheel may 
 be bolted directly to the cone pulley, and thus the fastest 
 of the three sjDeeds is obtained. The second is obtained 
 through the pinion ./, cast in one piece with the cone, 
 gearing into the toothed wheel g, and the pinion h gear- 
 ing into the wheel i, which must now be unbolted from 
 the cone pulley. On the back of the face-plate is bolted 
 a large internal spur-wheel, marked n. Into this gears a 
 pinion m on the end of the shaft d. This shaft lies below 
 the shaft c carrying g and h. Its level is seen in the side 
 and end views A and b. At its back end it bears the 
 wheel l that engages with the pinion k. This latter is 
 keyed on the back shaft c. The pinion m can be put in 
 or out of gear with the large internal toothed wheel by 
 sliding it along the shaft, there being a key slot in the 
 shaft and a feather in the pinion. When it is in gear, h 
 must be out of gear with i, and this latter must also be 
 unbolted from the cone pulley. This arrangement gives 
 the slowest speed of rotation, and is suitable for turning 
 very large diameters. 
 
 It may be observed that the bearings of the mandril 
 of this lathe are unsplit conical ones, and that the end 
 thrust is taken by a steel pin in the bridge, bolted to the 
 back end of the headstock in the manner previously 
 described. 
 
 30. Wheel-Lathe. — Fig. 39 shows a lathe specially 
 constructed for turning the tyres of locomotive and 
 waggon wheels. A is a side and b an end view. It 
 will be seen that there are here two slide-rests, the two 
 wheels being fixed on their axle before being put in the 
 lathe and the tyres being turned up simultaneously. 
 
 There are no face-plates to this lathe. The ends of the 
 wheel axle are clasped in cone chucks, which are then 
 bolted to the bosses of the spur-wheels l and l v These 
 occupy the usual place of face-plates. These outside 
 spur-wheels are driven by the pinions h and on the 
 
150 
 
 CUTTING TOOLS. 
 
 [Chap. VII 
 
 shafts i and i L . These carry the wheels h and gearing 
 with the pinions g and g v The latter are keyed on a 
 shaft f, that stretches the whole length of the bed. In 
 the centre of its length the shaft f_ carries keyed to it a 
 toothed wheel f and this engages with a pinion on the 
 end of a shaft d 1 that lies from the centre of the length 
 of the bed to the left-hand end of it. At this latter end 
 there is keyed upon d x the three-stepped cone pulley d , 
 on which the driving belt runs. 
 
 The mandrils bear two small wheels that drive the 
 similar wheels r and r L . These have discs with radial 
 slots in their faces, and a crank-pin fixed at the suitable 
 positions in these slots actuate a chain feed-motion 
 similar to that described for the lathe mentioned and 
 illustrated in Fig. 38. 
 
 There are other forms of lathes constructed for 
 special purposes, but those already described are 
 sufficient to illustrate the chief modifications to which 
 this important machine tool is subjected. The lathes 
 specially made for internal turning, or “boring,” are 
 described in a future chapter. The next chapter will 
 treat of the cutting tools used in the lathe and some 
 of the smaller appurtenances of the machine. 
 
 CHAPTER VII. 
 
 CUTTING TOOLS FOR LATHES. 
 
 1. Point of Application of Tool. — The points of 
 lathe tools are applied at the level of the centre 
 points. The tool requires to be held at a certain angle 
 to the direction of the cut — that is, to the tangent to 
 the circular section being formed. There is no special 
 difficulty in placing the tool at such a desired angle 
 
PLATE VIII. 
 
 a, Front View. 
 
 Fig. 39.— WHEEL LATHE. 
 
 B, Eight-hand End View. 
 
Chap. VII.] SETTING OF LATHE TOOLS. 151 
 
 whatever be its position above or below the centre 
 level, and it would also be easy to fix it in a tool-box in 
 any such position. But the slide of the tool-rest being 
 level, when the tool is advanced towards or withdrawn 
 from the line of the centres, it is evident that the tool 
 point remains always at the same level ; and if it is at 
 one distance, a certain amount, say, below the centre, then 
 it will be always below it by that same amount. In con- 
 sequence, if in one position it is set so as to be perpen- 
 dicular, or at any other definite angle to the cut, that 
 angle would not be maintained, but would become smaller 
 when the tool is advanced so as to cut a circle of smaller 
 diameter. If it is set right for one size of section, it will 
 not be right for any other size. This variation, however, 
 does not take place if the tool is placed at exactly the 
 level of the centre. It is in order to avoid the extreme 
 inconvenience of altering the setting of the tool anew 
 for each new size it has to turn that it is placed at the 
 centre level, and not, as is frequently imagined, because 
 this particular point of the section is in any essential way 
 specially suited for the application of the cutting thrust. 
 
 When the diameter of the wc*rk is large it makes no 
 appreciable difference in the cutting whether the tool is 
 a small distance higher or lower than the centre, because 
 on a large circle a small height corresponds to only a very 
 small angle ; but for small work a very little error in the 
 setting of the tool to the correct level makes a very con- 
 siderable difference in the angle between the tool and the 
 work, and makes a correspondingly great difference in the 
 cutting capability of the tool. 
 
 2. Since the edge is placed in this position, evidently 
 every part of the surface which it is at any instant cutting 
 stands vertically at that instant. The angle, therefore, 
 between any surface of the tool and the vertical is its 
 inclination to the direction of the cut, and the incli- 
 nation of any such face of the tool to the horizontal is 
 the same as the angle between it and the normal to the 
 cut surface. It is simpler to speak of these inclinations 
 
L52 
 
 CUTTING TOOLS. 
 
 [Chap. YIT, 
 
 to the vertical and horizontal, but in what follows it 
 must be remembered that the angles referred to are those 
 made with the cut surface and its normal, and that if, for 
 any special reason, the tool be placed higher or lower than 
 the centre level, the phraseology used in subsequent para- 
 graphs becomes literally incorrect. 
 
 8. Cutting Face; Top and Bottom Bake. — In all 
 lathes, with one exception/''' the surface being cut moves 
 vertically downwards , so that each portion of material 
 about to be separated in the form of a shaving lies 
 above the tool. The upper surface of the tool edge 
 is, therefore, that which forces the shaving aside, and it 
 is in consequence called the “cutting face” of the tool. 
 The chief point of importance in the formation of the 
 tool is the angle which this cutting face makes with the 
 horizontal, and this angle is technically termed the u top- 
 rake ” of the tool. There are curious differences between 
 different metals in this respect, some of them in being 
 cut requiring much more top-rake in the tool than others. 
 Different amounts of rake are also desirable, according to 
 the depth of cut taken on the same metal. 
 
 The angle between the under surface of the tool that 
 slopes downwards from its cutting edge and the vertical 
 is what Holtzapffel termed the “angle of relief,” and is 
 very commonly referred to as “ bottom-rake.” The only 
 object that there is in cutting away the under surface of 
 the tool in this way, and not leaving it vertical, is to avoid 
 its rubbing against the cut surface and thereby causing 
 unnecessary frictional resistance to the motion of the 
 lathe and the generation of injurious heat. It may be 
 shown that with ordinarily-shaped tools the cutting 
 point exerts a very considerable horizontal pressure in- 
 wards as well as a vertical pressure. This is easily 
 proved experimentally by loosening the collar on the 
 screw of the surfacing slide so that the tool-rest may be 
 
 * That of Whitworth’s, in which two tool-holders on opposite sides 
 of the work are used, the one tool being placed, as it were, upside 
 down. 
 
Chap. YII.3 
 
 BOTTOM-RAKE. 
 
 153 
 
 easily pushed in or out. If the lathe be started and a 
 cut be taken in this condition, the tool is immediately 
 pressed outwards by the work, so that the depth of the 
 cut rapidly diminishes to nothing. * The amount of the 
 radial pressure thus illustrated depends on the amount 
 of the top rake, the pressure being less the greater this 
 is. The radial pressure crushes the material inwards to 
 a minute extent. This springs outwards again imme- 
 diately it has descended below the cutting point, and the 
 result is that for a very small distance below this point 
 the surface is not actually vertical, but is inclined out- 
 wards from the vertical. If it were not for this, a much 
 smaller angle of relief than is necessary would be sufficient. 
 Professor Hart of Carlsruhe, whose work on machine 
 tools contains the best descriptions of this class of 
 machinery that has yet been published in book form, 
 gives as the proper angles of relief 4° for cast-iron, and 
 3°' for wrought-iron and gun-metal. The above-mentioned 
 projection of the surface under the point of the tool 
 extends, of course, for a minute distance only, and this 
 angle of relief is by no means necessary throughout the 
 whole depth of the tool. But if the surface be ground 
 to a straight bevel, it is impossible to give the requisite 
 angle to the top part of it without giving it throughout 
 the whole depth. There is no harm in grinding the sur- 
 face hollow, whereby less rake is given to the lower part 
 of it where it is not needed and more to the top, and 
 this method of grinding is often employed by workmen. 
 There is, however, no advantage in it, because the addi- 
 tional amount of metal left at the bottom in no way 
 strengthens the tool. 
 
 JSTo more bottom-rake should be given than is just 
 necessary to avoid friction between the tool and the 
 work. The solid angle of the tool edge, which is called 
 
 * This is so with tools whose cutting angles are upwards of 50° or 
 55°. With a larger amount of top-rake, however, there is often an 
 opposite tendency exhibited, namely, for the tool to run into a deeper 
 cut. 
 
154 
 
 CUTTING TOOLS. 
 
 [Chap. VII. 
 
 the cutting angle, equals a right angle minus the sum of 
 the angles of top and bottom rake. Thus the cutting 
 angle becomes less the greater either rake is made, and 
 the tool edge becomes weaker with the decrease of the 
 cutting angle. As has been proved mathematically in 
 Chapter V., when treating of planing tools, the greater 
 the top-rake is made the greater becomes the frictional 
 pressure of the shaving on the cutting face of the tool ; 
 but it is certain that within pretty wide limits the whole 
 thrust necessary to drive forward the tool is less the 
 larger the top-rake is. This angle is, therefore, made as 
 large as possible consistently with getting a cutting angle 
 such as will give sufficient strength to the edge. It is 
 for this reason that the bottom-rake must be made as 
 small as may be. 
 
 4. Cutting Angle. — Hart gives, as the result of a long 
 series of experiments, 51° as the best cutting angle for 
 wrought-iron, the same for cast-iron, and 66 Q for gun- 
 metal, these angles for lathe tools being the same as have 
 already been given for planing tools. He says that the 
 best angle is the same for all depths of cut. This last 
 statement does not, however, accord with the writer’s 
 own experiments, nor with common practice in work- 
 shops, where a somewhat greater amount of top-rake is 
 always thought advantageous for the heavier cuts. As 
 will be seen afterwards, the cutting force varies with 
 the depth of cut in such a way as to show that it is 
 probable that there is a special rake most suitable for 
 each depth of cut. 
 
 Hart’s experiments were directed towards finding the 
 angle that gave the least force required for cutting with- 
 out reference to the endurance of the tool edge. In 
 taking account of the due importance of getting the 
 edge to stand well without becoming dull, it is 
 found necessary to make the cutting angles larger 
 than the above amounts. The power required to cut is 
 increased very greatly by dulness of the edge ; in fact, 
 such dulness simply means the wearing away of the 
 
Chap. VII.] 
 
 CUTTING ANGLE. 
 
 155 
 
 accurately sharp edge, so that the real cutting angle 
 becomes very much larger than the apparent angle. 
 As it is impossible to be perpetually removing the tool for 
 the purpose of sharpening it, it would be absurd to start 
 with an edge such as will rapidly become blunt, even if it 
 has the angle which is proved to be best, because it will 
 rapidly lose that angle and be converted so as to have 
 an angle much worse than would be left after the same 
 amount of work if at starting the edge had been made 
 not quite so keen. The actual cutting angle commonly 
 used on wrought-iron and steel for heavy cuts is, there- 
 fore, 10° or 12° greater than the above, while for cast- 
 iron it is best made a few degrees still greater. 
 
 If the cutting angle be 65° and the bottom-rake 3,° 
 these leave 22° as the angle of top-rake. These are 
 probably about the best angles for ordinary roughing- 
 out work in wrought-iron and steel, while a few degrees 
 larger cutting angle is suitable for cast-iron, and about 
 80 p for brass. In finishing, the angles are often left 
 unchanged, but a better result may be obtained by 
 increasing the cutting angle in each case by from 5° to 
 10°. 
 
 5. Faulty Formation of Cutting Face. — It would 
 be very easy to obtain what- 
 ever amount of top-rake is 
 desired at every part of the 
 cutting edge if the cutting 
 edge were simply one straight 
 line. This is approximately the 
 case with tools used for taking 
 finishing cuts. The depth of 
 shaving is here very small, and 
 its breadth comparatively large. 
 
 All except a very small length 
 at the forward corner of the Fig. 40 . 
 
 edge is parallel to the finished 
 
 surface of the work. But it is not so when deep cuts 
 are being taken. Fig. 40 represents the plan of a tool 
 
156 
 
 CUTTING TOOLS. 
 
 [Chap. VII. 
 
 point that is being traversed to the left-hand and has 
 cut along the line ctb, the depth of shaving being the 
 distance between the lines do and ha. The section of 
 the shaving being removed is shown between the 
 full line ebb 1 and the dotted line ce l b l . The portion of 
 the cutting edge that is in operation is the curved line 
 ebb 1 . The length bb 1 , which equals the amount of 
 traverse-feed per revolution of the work, is parallel to 
 the finished surface b Y a, and the portion correspond- 
 ing to bb 1 (i.e., of which bb 1 is a plan) of the surface 
 in the act of being cut is vertical and parallel to the 
 axis of rotation. The portion of this surface near e, 
 however, is vertical and perpendicular to the axis of 
 rotation. Between e and b there is a series of strips of 
 this surface that are all vertical, but have all shades of 
 inclination to the axis of rotation. Suppose, for the sake 
 of simplicity of statement, that be is the quadrant of a 
 circle, then the cut surface immediately below it forms 
 a quadrant of a vertical cylindrical surface of circular 
 sectioji. The under surface of the tool should be equally 
 inclined at all points of the cutting edge to this cylin- 
 drical surface, namely, at an angle of 3°. It should, 
 therefore, be ground to the form of a cone, the angle 
 at whose apex is twice 3°, or 6°. 
 
 There is no difficulty in so grinding this under sur- 
 face at 3° to the horizontal plane at every point of the 
 cutting edge, whether this be circular or of any other 
 shape. Similarly the upper face of the tool should be 
 inclined at 25° to the horizontal plane at every point of 
 the edge, and if this be circular, the result would be that 
 the upper face should be shaped as a hollow cone whose 
 apex angle is (180° — 2 x 25°) = 130°. This is impossible 
 to perform accurately by any process of grinding or other 
 means of renewing the sharpness of the edge. But it is 
 to be observed that only the front and one side of the 
 plan of the point are employed as cutting edges, and that 
 the hollow upper face need not be conical all round. If 
 one quarter of the hollow cone were formed, the rest of 
 
Chap. VII.] 
 
 TOP-RAKE. 
 
 157 
 
 the surface to the right-hand side might be left open, 
 sloping downwards as a continuation of the left-hand 
 conical part. A trough of this sort that will give 
 approximately the quarter-cone surface on the cutting 
 side can be ground out on a small-sized emery-wheel 
 with a round edge. 
 
 Such an upper surface is not often given to their 
 turning tools by workmen, but it is to be strongly 
 recommended, and many intelligent turners produce a 
 hollowed top-face that is in effect not greatly different 
 from that described. The trough they give the tool has 
 curvature in one direction only, this being the fault of 
 the grindstone or emery-wheel being too large in diameter, 
 since the proper double curvature can only be produced 
 on a wheel of very small size ; and it has, besides, the 
 other fault of being ground too straight across the tool, as 
 seen in plan, instead of obliquely at an angle of from 30° 
 to 60° to the tooled surface according to the shape of the 
 point in plan. 
 
 6. Side-Rake. — These remarks apply to all lathe tools 
 with rounded points, or “ round-nosed ” tools, as they 
 are called. All such tools are gradually traversed in 
 one direction or the other, and, therefore, the cutting 
 portion of the edge is confined to the front part, parallel 
 to the work and to one side. The tool never cuts on both 
 sides of the front part. 
 
 The angle of inclination to the horizontal of the part 
 of the cutting face lying immediately behind the front of 
 the edge is called the front top-rake ; that of the portion 
 sloping away from the side of the edge is called the side 
 top-rake. 
 
 If the cutting face be ground flat, with its plane 
 parallel to the centre line of the lathe, there can evidently 
 be no side-rake on the tool. Such a tool is very disad- 
 vantageously formed for a deep cut and a traversing 
 motion. This form is much used, however, especially 
 for finishing cuts. Evidently it may be traversed equally 
 well in either direction. It may be termed a u front tool.” 
 
158 
 
 CUTTING TOOLS. 
 
 [Chap. YII. 
 
 Tools with side-rake can evidently be used each with 
 a traverse in one direction only. A tool ground for a 
 traversing motion towards the left-hand cannot be used 
 with a motion towards the right-hand. Side-rake must, 
 therefore, be distinguished as left-hand and right-hand, 
 the former being that in a tool whose side cutting edge 
 lies to the left-hand of the tool, and whose left-hand edge 
 is, therefore, higher than its right-hand edge. 
 
 A tool without any side-rake not only cuts much 
 worse at its side edge, but also requires a large amount of 
 force to move the slide-rest in its traversing motion so as 
 to make the tool feed forwards. A tool which is given 
 the full due amount of side-rake, on the contrary, requires 
 very little power to drive it onwards in its traversing 
 motion, and a correspondingly small amount of wear 
 takes place in the self-acting feed-gear, whether that be 
 a rack and pinion or a leading-screw and nut. In a book 
 entitled “ The Complete Practical Machinist,” by Mr. 
 Joshua Pose, an American mechanic, it is said that 
 sufficient side-rake may be given to a tool to cause it to 
 feed itself into its cut — i.e., to require no force to be 
 applied to the slide-rest to draw it along the bed. 
 
 7. Straight-edged Tools. — Straight-nosed tools, as 
 distinguished from round-nosed, are those whose cutting 
 edges are straight lines. The edge may be a single 
 line, and this line may be either horizontal or inclined 
 to the horizontal, and in either case the line must lie 
 in a vertical plane parallel to the line of centres. 
 For finishing, a single straight-line edge, very slightly 
 inclined to the horizontal, is very suitable. The effect 
 of the inclination of the edge on the sectional shape 
 of the shaving is the same as if the edge were very 
 slightly rounded, i.e., to an extremely flat curve. The 
 cutting face slopes slightly downwards to the right, be- 
 sides slanting backwards for top-rake, and thus the shav- 
 ing is thrown off easily, curling over to one side. The 
 under front face (that to which bottom-rake is given) 
 should not be ground so as to be parallel to the line of 
 
Chap. VII.] 
 
 STRAIGHT-NOSED TOOLS. 
 
 159 
 
 centres, but should lean a little towards it on the right- 
 hand side, the effect of this being to keep the edge in the 
 vertical parallel plane above-mentioned from which it 
 would deviate if this were not done. 
 
 The edge may also be made up of two straight lines. 
 The angle between them is very various in actual tools. 
 Tools for cutting screw-threads are given the angle 
 desired in the groove between the threads. Other tools 
 are specially formed for cutting out rectangular corners, 
 and in them the angle between the two parts of the edge 
 is made 3° or 4° less than a right angle, so as to enable the 
 point to get into the exact corner without both the edges 
 cutting simultaneously. These corner tools are usually 
 required to be bent round in a horizontal plane to the 
 right or left hand for opposite situations of the corner, 
 and they are called right and left hand tools according as 
 they are bent right or left. 
 
 Sharp-pointed tools with two straight edges meeting 
 at the point are sometimes used for plain cutting with a 
 traversing feed. The surface cut by such a tool is evi- 
 dently a Y-threaded screw. There does not appear to be 
 any advantage in this form. Both edges cut. Professor 
 Willis investigated the geometrical properties of such a 
 tool with a flat upper face, with the result of showing it 
 to be impossible to combine fair cutting angles with 
 sufficient strength. The whole value of Professor Willis’s 
 investigation lies in this negative result : he recommends 
 the above form of tool, but on mistaken grounds. The 
 objection to it is that there is a back cutting edge as well 
 as a forward one, which makes it impossible to use side- 
 rake. This fault in the tool is removed by grinding off 
 the sharp point (which is in any case sure to become 
 worn away rapidly) with a small straight or slightly- 
 rounded facet, of a breadth rather more than the greatest 
 traverse feed to be used with the tool. The cutting 
 edges then become one of the oblique sides only and the 
 facet, and, the other edge becoming then of no use, side- 
 rake may be applied. If the symmetrical form of the 
 
160 
 
 CUTTING TOOLS. 
 
 [Chap. VII. 
 
 tool is to be preserved so that it may be used with a 
 traverse in either direction, then the advantage of having 
 the right cutting angle at some portion of the edge must 
 be sacrificed. 
 
 8. Side Tools. — When a large plane surface perpen- 
 dicular to the line of centres is to be turned, the tool is 
 clamped in the rest with its shank at right angles to the 
 surface. This is possible so long as a cylindrical continua- 
 tion of the work standing out from the plane surface does 
 not interfere with the tool-rest moving into position, so 
 that the tool may reach the inner portions of the plane. 
 At this inner corner, however, the tool-rest could not be 
 advanced sufficiently near the centre, and recourse must 
 be had to a “ side tool ” clamped in the rest, with its 
 shank parallel to the plane turned surface. This is a tool 
 with its end set out to one side, so that a straight side- 
 cutting edge may be formed on it, which may operate on 
 a surface from which the body of the tool stands clear 
 by a small distance. The cutting edge may be made 
 long or short, according to the work to be done. It stands 
 radially along a horizontal diameter of the plane surface 
 being wrought, and all the rake required is side-rake. 
 All faces of collars on shafts, etc., and similar work, musl 
 be treated so. If the collar is not deep, an ordinary right 
 or left hand corner tool may be sufficient ; but if it is a 
 large one with a broad surface, side tools must be used 
 with which to finish off the plane faces. 
 
 9. Springing' of the Tool. — It has already been said 
 that if the tool be not held firmly up towards the work 
 it wfill “run out of its cut.” It will do so, at least, 
 unless an excessive amount of top-rake has been put 
 upon it. There is, however, an opposing influence 
 which sometimes tends to make the tool cut deep when 
 it meets with any extra resistance. This is the plia- 
 bility of the tool itself. If the tool bends, its edge 
 shifts its position relatively to the work and moves 
 to a greater or smaller distance from the centre of the 
 work, according to whether the direction of its motion 
 
Chap. Yf TJ 
 
 SPRINGING OF THE TOOL. 
 
 161 
 
 lies within or without the periphery of the section being 
 turned. As the edge stands at the same level as the 
 centre of the work, it follows that if the centre about 
 which it moves in consequence of the bending of the tool 
 lie above the horizontal diameter of the work, the edge 
 will be thrown farther from the centre, and will cut a 
 section of larger size than is intended. If, on the other 
 hand, it be below this level, bending of the tool will cause 
 the edge to move inwards — to “ spring into the work,” 
 as it is called — so that the section cut will be too small. 
 If the bending cause the edge to move round a centre on 
 the same level as the centre of the work, then for a very 
 small amount of bending the effect will be almost nil, 
 and large amounts of bending cause less variation in the 
 turned section than if this centre of movement be situated 
 anywhere else. 
 
 In order to ensure that the tool should, rather spring 
 out than into the cut, it is recognised as a principle that 
 the cutting edge should not stand higher than the top 
 surface of the shank. To obtain the upward slope 
 giving top-rake, it is therefore necessary to have the 
 front portion of the top surface hollowed or cranked. 
 This is very commonly attained by simply grinding out a 
 portion of the top of the straight shank. This is quite 
 satisfactory in a very stiff tool ; but if the shank be not 
 strong, the process evidently leaves the weakest part, 
 round which bending must occur, underneath the hollow, 
 i.e., at a point below the level of the edge, which will, 
 therefore, not spring as desired. 
 
 With the same object in view, the front end of the 
 shank is very frequently forged in the shape of a crank. 
 This results in the edge being considerably lower than 
 the top of the body of the shank. Such a too], therefore, 
 whenever it bends at all, springs outwards. Several 
 different forms are given to the cranked end, all, however, 
 having the same object, but chiefly differing in the 
 amount of pliability given to the tool. Some, such as, 
 for instance, an upward cranked tool for finishing cuts 
 L 
 
162 
 
 CUTTING TOOLS. 
 
 [Chap. VII. 
 
 on brass, are purposely designed to be pliable and give 
 wav before differences in the resistance. 
 
 In general, however, it is very valuable to remember 
 that what is of chief importance is to keep the tool edge 
 constantly at the same distance from the centre of the 
 work, and that for this purpose it is much more effi- 
 cacious to ensure that the tool will not bend at all 
 appreciably than to ensure that it will bend in any 
 particular direction. To produce accurately true work, 
 it is, best to make the tool in the first place as stiff as 
 possible, and after that is provided for attention may be 
 turned towards the problem of arranging that whatever 
 small amount of bending is absolutely unavoidable should 
 move the edge in a vertical line. 
 
 10. Tool-holders. — In a previous chapter the great 
 advantages of using small pieces of steel inserted in the 
 extremity of a stout iron bar as tools were explained in 
 the case of planing-machines for metal. These advan- 
 tages have been more extensively recognised in their 
 application to lathe work than in any other application 
 probably because there is much more lathe work done 
 than machine work of any other kind. The iron tool- 
 holders with small inserted tools have, therefore, become 
 very common in turning, and several patterns of tool- 
 holder are extensively sold. 
 
 The first form that had wide practical success was 
 Smith and Coventry’s “ round steel tool-holders.” Fig. 41 
 illustrates this design. The tool-holder is a stout bar 
 of square iron which is cranked at its forward end. At 
 the front end of the crank, immediately behind the point, 
 is bored a hole of small diameter downwards through the 
 whole thickness of the iron. This hole is oblique to the 
 vertical, slanting backwards and downwards, and also 
 either from right to left, or vice versd. In this hole is 
 inserted a short round bar of steel, which is the cutting 
 tool, and whose diameter is very slightly less than that 
 of the hole. The upper end of this is ground off obliquely, 
 so as to give an elliptical section. This section forms 
 
Chap. VII.] 
 
 TOOL-HOLDERS. 
 
 163 
 
 the cutting face, and the cutting edge is the highest sharp 
 corner of the ellipse. The tool is, therefore, a round- 
 nosed one. The piece of steel is fixed at the proper 
 height by a small steel set-screw passing through one 
 side of the extremity of the iron holder and entering 
 the hole. This screw pinches 
 the tool - steel against the 
 opposite side of the hole. 
 
 When the tool is re-ground, 
 it is pinched in a slightly 
 higher position than pre- 
 viously, so as to make up for 
 the shortening of its length 
 and keep the edge at exactly 
 the same level as before. The 
 object of the lateral inclina- 
 tion of the hole and of the 
 tool inserted in it, is to give 
 the same effect as that ob- 
 tained by bending the shank 
 of a solid tool to one side 
 
 or the other. The tool thus ... a ... . « , , 
 
 Fig. 41.— Smith, and Coventry’s 
 
 acts as a Side or corner tool. Round Steel Tool-holder. 
 
 A pair of tool-holders is, 
 
 therefore, necessary, one left-handed and the other right- 
 handed, with the hole for the insertion of the steel-tool 
 correspondingly inclined. 
 
 These tools are found to cut very well indeed, but 
 with a deep heavy feed the pinch-screw does not hold 
 the steel sufficiently firmly to withstand the strain, and 
 the steel is therefore apt to slip downwards a little, 
 thereby causing inaccuracy in the work, which may 
 easily be overlooked if the slipping takes place gradually. 
 In the diagram (Fig. 41) it will be observed that between 
 the upper front edge of the holder and the hole the 
 supporting metal is necessarily very thin. This is a 
 decided fault in the design because it is here that the 
 chief pressure has to be sustained. Consequently it is 
 
164 
 
 CUTTING TOOLS. 
 
 [Cliap. VII. 
 
 found ill practice that this thin strip of metal bursts 
 sooner or later, and it then becomes impossible to hold 
 the tool up to its work steadily.* These faults do not 
 affect the efficiency of the instrument for light work ; 
 and, therefore, the great simplicity of the tool, its cheap 
 
 Fig. 42. 
 
 form, and the ease with which it can be re-ground and 
 renewed when worn out, make it very suitable for 
 small lathes and for finishing cuts. 
 
 Smith and Coventry have more recently brought 
 out another tool-holder which possesses many advantages 
 over their earlier patent. This is shown in Fig. 42. In 
 it the shank is again of square section. Its front end 
 is forged into the shape of a short vertical cylinder or 
 
 * In. Messrs. Smith and Coventry’s own works these defects are 
 said not to have been felt, probably because their workmen have been 
 more carefully instructed in the proper mode of using the tools, and 
 have had a more prolonged experience in their use than has been 
 gained elsewhere. Messrs. S. and C. prefer these tools to their swivel 
 tool-holder. 
 
Chap. VII.] 
 
 TOOL-HOLDERS. 
 
 165 
 
 boss. Through this is drilled a vertical hole of about one- 
 third the diameter of the outside of the boss. Through this 
 hole is placed a bolt, its head being below and a nut 
 above the boss. Through the centre of the bolt, imme- 
 diately over its head, is cut a vertical rectangular slot, 
 and through this is passed the small piece of' steel of 
 tapered section that performs the cutting. The thickness 
 of the top of this steel is greater than its thickness at its 
 lower side, in such a proportion that s the two sides slope 
 towards each other at an inclination of about 6°. An 
 example of the dimensions has already been given in 
 Chapter V. : namely, depth = top thickness = T 9 -g", 
 bottom thickness = Other sizes have the same pro- 
 portional dimensions. When this is held upright, each 
 side is inclined at about 3°, the proper angle of relief for 
 the under surface of a metal-cutting tool. In order to 
 ensure that the steel is held upright, a notch is cub 
 centrally across the upper face of the head of the bolt 
 of the proper width to allow the thin under side of the 
 tool-steel to enter it. Over the tool, and between it and 
 the under surface of the boss of the holder, comes a strong 
 washer, and across its lower face is cut a diametrical 
 notch of just the right width to admit the top of the 
 tool-steel. These two notches prevent the possibility of 
 the steel leaning to one side of its upright position. 
 They are cut so as to have one side higher than the 
 other. The tool-steel lies, therefore, with its upper face 
 inclined to the horizontal, the notches being cut so that 
 this inclination is a good average value for the ordinary 
 top-rake required. The forward end of the steel is ground 
 to any desired shape of cutting point, and the steel can 
 be swivelled along with the bolt and washer, so as to 
 stand at any horizontal angle with the axis of the work, 
 while the shank of the holder itself always remains per- 
 pendicular to that axis. When the tool has been set in 
 the desired position, all the parts are tightly bound 
 together by screwing up the nut on the top of the boss. 
 The same tool-holder can be used right and left hand, or 
 
166 
 
 CUTTING TOOLS. 
 
 [Chap VII. 
 
 the steel may be set to act as a front tool. The great 
 advantage which this and no other tool-holder possesses 
 is that the steel may be set so readily to any exact 
 horizontal inclination, according to the peculiarities of 
 shape of the work being operated upon. The shape of 
 the steel used for the tool gives it great strength and 
 stiffness, and allows it to be ground with any desired 
 rake with facility. The clamping arrangement is neat, 
 compact, and perfectly trustworthy; and, altogether, it is 
 probable that a better tool-holder for the lathe cannot 
 be designed. It has one defect, namely, that when great 
 side pressure is put on the tool by a heavy cut the tool is 
 apt to be swivelled round slightly by this side force, and 
 so to cut deeper into the material. This may easily be 
 remedied, without sacrificing the horizontal angular ad- 
 justability, by ribbing the upper surface of the washer 
 and the under surface of the boss against which it is 
 clamped, after the manner of a rose-drill. 
 
 Fig. 43 shows a third tool-holder, made by Tangye 
 Brothers. It is similar in princijDle to that last 
 described, but differs from it in several points. The 
 tool-steel used is of the same shape, and it is held in a 
 rectangular vertical slot. The slot is, however, made in 
 the solid boss forming the extremity of the shank, there 
 being no loose bolt passing through this. The steel is 
 clamped in this slot by a wedgo or by a set-screw that 
 penetrates vertically through the boss. There are three 
 such slots through the boss, which intersect each other in 
 the vertical axis of the boss. One is directed straight for- 
 ward, and when the steel is placed in this it acts as a 
 front tool. The two others are equally inclined to the 
 right and left of the central slot. When the steel is 
 placed in either of these, it becomes a right or left hand 
 side tool. These slots are inclined to the horizontal in 
 the same manner as in Smith and Coventry’s, at the 
 angle of average top-rake required. The superiority that 
 Messrs. Tangye Brothers claim for this design is that the 
 whole holder being in one solid piece, with the exception 
 
Chap. YII.] 
 
 TOOL-HOLDEBS. 
 
 167 
 
 of the small clamping-wedge or set-screw, there is greater 
 solidity and less liability for the tool to shift its position 
 horizontally if undue cutting stress be thrown upon it, 
 than in Messrs. Smith and Coventry’s system. They main- 
 tain that two side positions of the tool are amply sufficient 
 for all work, and that a slight variation of the horizontal 
 
 inclination of the side tools can be obtained by clamping 
 the shank obliquely in the tool-rest. The writer thinks, 
 however, that the variability of this inclination obtained 
 in the previously described holder is of great advantage, 
 and the method of clamping is also decidedly more 
 secure. 
 
 11. Springing of the Work. — The inaccuracy in the 
 work caused by the springing of the tool has already 
 
1GS 
 
 CUTTING TOOLS. 
 
 [Chap. VI I. 
 
 been mentioned. The same kind of inaccuracy results 
 
 «/ 
 
 if the piece being turned bends in consequence of the 
 pressure applied to it by the tool. 
 
 It was shown that if the shaving were at every point 
 of the same thickness and offered the same resistance to 
 cutting, the tool would always be bent by exactly the 
 same amount, and would, therefore, still cut a truly 
 circular section in spite of its springing. In the same 
 manner, if the resistance to cutting remained uniformly 
 the same from point to point, and if the work be sym- 
 metrical round its axis from end to end so that it bends 
 equally easily in all directions, then as it rotates the 
 bending would take place in a plane that maintained 
 always the same position relatively to the lathe bed 
 and rotated relatively to the work at a uniform rate, 
 mid the amount of the bending would from instant 
 to instant remain the same. If this were the case, 
 the section turned would still be truly circular, In 
 consequence, however, of the work being not truly 
 cylindrical, to begin with, a thicker and more resistant 
 shaving must be taken off one side than off the other. 
 The work bends, therefore, more at one part of its revo- 
 lution than at another, and the result is that the section 
 cut is not a circle truly concentric with the axis of rota- 
 tion. In taking the second cut, therefore, there is still 
 an inequality in the thickness of the shaving to be taken 
 from opposite sides. uThe same difficulty, therefore, 
 occurs a second time, but the resulting error after the 
 second cut is not nearly so great as that after the first 
 cut, not only because the variation in bending has been 
 greatly reduced by the first cut, but also because the 
 second shaving taken off is not nearly so thick, and 
 therefore not so resistant, as the first was, and thus the 
 whole amount of bending is much smaller than it was 
 before. By successive approximation, therefore, the 
 truly circular section is at last obtained. In order to 
 produce very accurate work, it is sometimes necessary to 
 take two or three finishing cuts. 
 
Chap. VII.] 
 
 BACK STEADY-REST. 
 
 169 
 
 12. Back Steady-Best. — There is still another way, 
 however, in which the bending affects the work. Any 
 force applied near the centre of a beam bends it much 
 more than does the same force applied near its point 
 of support. The cutting effort of the tool, therefore, 
 bends the work much more when the slide-rest is 
 nearly midway between the centres than when the 
 tool acts close to the ends of the work. If the tool 
 be traversed in a line accurately parallel to the axis 
 of rotation, the result of this is that the size of the 
 section , cut near the middle of the length will be 
 greater than that of the end sections, so that the 
 work produced is not truly cylindrical. This effect is 
 also reduced by gradually diminishing the depth of suc- 
 cessive cuts, i.e. } by taking “finishing” cuts. But in 
 long and slender pieces, such as shafts, the error pro- 
 duced in this way would be so large, and would require 
 so many repeated cuts to get rid of, that ut is necessary 
 to provide other means of avoiding it. This is effected 
 by the use of what is called a “ back steady-rest.” A 
 stiff upright bracket is bolted to the back of the saddle 
 of the slide-rest, and is, therefore, traversed along with 
 the tool. This carries at its top a bearing, which can be 
 adjusted in position so as to support from behind shafts 
 of larger or smaller size. The bearing consists simply of 
 a block of cast-iron, with an internal right angle formed 
 in its front side, in which angle the turned shaft lies. 
 The one side of the angle lies vertically over the shaft, 
 so as to prevent its rising before the tool pressure. The 
 other leg of the angle supports the shaft at the back 
 extremity of the horizontal diameter, and prevents its 
 yielding horizontally. The support is not applied directly 
 opposite the tool, but as short a distance behind it as 
 possible on the portion that has already been cut. In 
 starting from one end, the workman turns a short length 
 before adjusting the steady-rest, the bending at the end 
 being so slight that no support is needed. He thus gets 
 a short length turned down to the required diameter, and, 
 
170 
 
 CUTTING TOOLS. 
 
 [Chap. VII. 
 
 the rectangular bearing being set to this, it continues, 
 travelling behind the tool, to be in exact adjustment 
 so long as the diameter of the section cut remains the 
 same. 
 
 A considerable amount of frictional resistance arises 
 at this bearing, and it should be kept continually well 
 lubricated. Such steady-rests are not usually, but they 
 ought to be, supplied with a drip-oil or soap-water can 
 for the efficient lubrication of the bearing. 
 
 13. Capstan Tool-rest and Hollow Mandril. — A 
 very convenient modern form of tool-rest for special 
 work, called a “ capstan ” rest, may be mentioned here. 
 This is a thick cylindrical plate in the place of the 
 ordinary top plate and tool clamps of the slide-rest. In 
 the periphery of this disc is a number of square holes, in 
 which differently shaped tools may be fixed by set-screws 
 through the top of the disc. The plate, with the tools 
 thus fixed in it, can be swivelled round into as many 
 positions as there are tools, and is caught and held in 
 these positions by a spring catch entering a corres- 
 ponding series of notches in the plate. Thus, any one 
 of the set of tools may be brought to the front, and used 
 on the work. Such a rest is extremely convenient when 
 a large number of copies of an object of small size is to 
 be manufactured, and the turning of which necessitates 
 or is facilitated by the successive use of several tools. 
 Each of the copies occupies only a small time in actual 
 turning, and if to the time thus actually utilised were to 
 be added that needed to take out of the rest one by one 
 every tool needed in the series of operations, and to insert 
 each in turn, the proportionate waste of time would be 
 very great. This is obviated by the above tool-rest. 
 Without it, time may be economised by performing 
 one of the operations on a large number of the copies ; 
 then changing the tool, and proceeding to the second 
 operation on the same number again; and so on. But 
 this necessitates the taking of each object out of the 
 lathe and putting it in again many times. There is 
 
Chap. VII. ] 
 
 CAPSTAN TOOL-REST. 
 
 171 
 
 the same objection to having the various operations 
 performed by different men at different lathes, the 
 article being passed on from one hand to the next. 
 In some instances the waste of time is not the only 
 objection to such a method. If, for instance, a number 
 of pins of any special pattern have to be turned, these 
 are best made in a “ hollow mandril ” lathe. The rod 
 out of which the pins are to be manufactured is passed 
 through the hollow mandril, and chucked so that a short 
 length of its end only projects. This is operated on suc- 
 cessively by the various needful tools fastened in a 
 capstan rest, the last of which, when the pin is finally 
 complete, cuts it off the end of the rod. The rod is 
 then drawn farther through the hollow mandril, gripped 
 once more, with the exact required length projecting 
 (measured by the end being drawn up to a stop-gauge), 
 and the process repeated. For such work two of the tools 
 invariably needed are a roughing-out took and a cutting- 
 in tool. Then there may be a tool for finishing parallel 
 parts and another for finishing flat faces. Other tools may 
 be wanted to round off, or shape to any given profile, 
 different corners, for which purpose it is convenient 
 to have special profiling tools made whose edges are cut 
 to fit to the exact contour desired. These tools, being 
 difficult to make and to re-sharpen, should not be made 
 to do any heavy duty, but should be used only to finish 
 off with, the shape having been got approximately with 
 roughing-out tools. Hollow mandril lathes are useful for 
 a great variety of purposes, and their efficiency is greatly 
 increased by being provided with capstan tool-rests. 
 These rests have been chiefly introduced by Messrs. 
 Smith and Coventry. 
 
 14. Boring Collar. — A long object that for ordinary 
 outside turning would be placed between the centres, 
 sometimes requires to have a hole bored along its 
 axis from one end, and it may be convenient to do 
 this in the lathe. As in this case the centre of the 
 work is not available for its support (because the tool 
 
172 
 
 CUTTING TOOLS. 
 
 [Chap. VIL 
 
 is operating at this point), a special support is needed. 
 This is supplied by a strong stiff plate bolted to the 
 bed of the lathe at just the right distance from the 
 fast headstock to admit the object to be bored between 
 the steel centre on the mandril and a hole bored in the 
 plate. The centre of the hole is placed so as to lie in 
 line between the centres on the two headstocks. The 
 hole is made of the size of the end of the object, and is 
 chamfered or counter-sunk so as to provide a conical bear- 
 ing for that end. The object running in this conical 
 bearing is at once kept to the centre, and end pressure is 
 also supplied similar to that exerted by the steel point 
 of the poppet-head. If the object may have a short 
 length turned down so as to leave a shoulder, it is better 
 to have the hole in the centre plate parallel, and to allow 
 the shoulder to bear against the surface of the plate. 
 There is sometimes, however, not sufficient metal for 
 this. For example, if a number of long tubes of thin 
 metal are to have the ends faced off, and perhaps the 
 interior bored out for a short length for the insertion of 
 a socket of some sort, or perhaps to have their interior 
 ends screwed in the lathe, a plate of this sort with a 
 conical bearing is the only method of supporting them, 
 unless a loose collar be clamped on the end temporarily. 
 
 Such a centre plate has been given the name of 
 “ boring collar.” Attention should evidently be paid 
 to keeping it well lubricated. 
 
 15. Chasing Tools. — All screws that are required to 
 be accurate are, as has been previously mentioned, 
 cut by traversing a single pointed tool shaped so as 
 to fit into the grooves desired to be left between the 
 rounds of the thread, the traverse feed motion being 
 made strictly uniform by being operated by a care- 
 fully made “leading screw.” The requisite traverse 
 motion may, however, be given to a hand tool by 
 the pressure between the tool and the work itself. 
 The under surface of the tool is composed of two 
 nearly vertical faces meeting in a sharp edge that is 
 
Chap. VII.] 
 
 CHASING TOOLS. 
 
 173 
 
 pressed into and becomes buried in the work. This 
 edge is inclined laterally to the vertical, at the inclination 
 the thread is desired to have to the cross section of the 
 screw, and, sliding in the groove which the tool itself 
 cuts, guides the advance of the tool along a spiral line 
 always having this same inclination. Such tools are 
 called “ chasing tools.” In order the better to keep 
 the inclination and, therefore, the pitch of the screw 
 uniform, several cutting points one behind the other are 
 given to the tool. The inclination of the leading edges is 
 to the right or left according as the screw is to be a 
 left-handed or a right-handed one. Chasing tools are 
 made both for outside and inside screws, the former 
 having their edges placed on the shank like a front tool, 
 and the latter having them placed on the side parallel 
 to the length of the shank, so that the shank may be 
 held parallel to the axis of rotation and pass into a 
 narrow hole. 
 
 There is always considerable difficulty in starting the 
 cut with these tools at the exact right inclination. It is 
 impossible to produce accurate screws by their means ; 
 but for the majority of screws no great accuracy is 
 required, and for them the work produced by chasing 
 tools is quite sufficiently good. As, however, much 
 simpler and more rapid means of producing such 
 screws — namely, by “dies” — -are usually at hand, 
 chasing tools are very little used in modem workshop 
 practice. 
 
 16. Experiments on Cutting Pressure on Tool- 
 point in Lathe. — As has already been said, the cutting 
 force required in lathes varies rapidly with the depth 
 and breadth of shaving turned off. One large portion 
 of the power consumed by a lathe is expended in over- 
 coming the friction of the journals, in bending the belts 
 whose stiffness resists their motion round the pulleys, 
 and in driving the traversing gear of the slide-rest. The 
 chief point of scientific interest, however, is to discover 
 that part of the power actually spent in the removal of 
 
174 
 
 CUTTING TOOLS. 
 
 [Chap. VII. 
 
 the shaving. To find how this varies with the depth of 
 cut, with the breadth of the traverse feed per revolution, 
 and with the velocity of cutting, the writer carried out a 
 series of experiments at his works in London, in which 
 he was assisted by Messrs. Charles Hambly and George 
 Hunt, turners by trade. A Smith and Coventry’s swivel 
 tool-holder was used in these experiments. Measure- 
 ments were taken under 240 different conditions as to 
 cutting speed, depth of cut, and amount of traverse feed. 
 One hundred and twelve of these experiments were made 
 in cutting cast-iron, 64 in cutting forged steel, and 64 on 
 bar-iron. Two tools were used on the cast-iron, the 
 first tool made proving to have been tempered too soft. 
 The second tool was ground to exactly the same shape 
 and cutting angle as the first, and was hardened in 
 salt water. It lasted very well, not requiring to be 
 re-sliarpened throughout the whole of the remaining 
 experiments on cast-iron, 64 in number. Nearly all 
 the rake was put on the side of the tool, which was 
 shaped with a round nose suitably for a moderately heavy 
 cut. The cutting face was ground so as to leave an 
 angle of top-rake on the side of 24°. One and the 
 same tool was used throughout the 128 measurements 
 on iron and steel. Nearly all its rake was on the side, 
 the angle of top-rake being 46 1°, and the edge being 
 round-nosed. This tool was hardened by being quenched 
 right out in water in which salt and wheaten flour 
 were mixed, and without any subsequent tempering. It 
 stood remarkably well, not requiring any sharpening 
 throughout 112 experiments, in each of which it cut 
 a length of shaving corresponding to about inch 
 traverse on a mean diameter of 2-| inches. Its edge 
 then slightly broke in taking a cut 0*14 inch deep on 
 wrought-iron of inferior quality with a good deal of dirt 
 in its texture. The tool was then re-ground to the same 
 form as before, and lasted well for the remaining 16 
 experiments, in each of which a cut 0*14 inch deep was 
 taken on the same wrouglit-iron. 
 
PLATE IX. 
 
 * Cutting Force in tbs • 
 Wrought iron . 
 
 Fig. 44 .- Curves co-ordinating the Cutting Forces exerted by the Points op Turning-tools, with the Brfadths 
 op Shaving^ removed. Each Curve is for one constant Depth of Cut, which is marked on the Curves in 
 Figures as the fraction of an inch. 
 
Chap. VII.] EXPERIMENTS ON CUTTING FORCE. 
 
 175 
 
 The east-iron operated on was of good soft quality, 
 such as is usually termed pulley-metal. The diameters 
 cut were 16f inches, 7 inches, and inches. The 
 measurements taken from the two larger diameters 
 were slightly irregular ; but, so far as could be judged, 
 the difference in diameter made little or no difference in 
 the force required for cutting, other conditions being the 
 same. 
 
 The steel used was tough, a waste crank-shaft forging 
 of inches diameter being used. 
 
 The wrought-iron was common bar of inferior quality, 
 the diameter being 2| inches. 
 
 Throughout all the experiments the tool was carefully 
 kept in the same position in the swivel tool-holder, and 
 all the cuts were taken without any water or other lubri- 
 cant being applied to the tool point. 
 
 The tool-holder had a ^ inch hole drilled through its 
 shank parallel to the axis of the work, at a short distance 
 from its front end. A steel pin was driven through this, 
 fitting tightly in the hole. A wrought-iron block had a 
 deep groove cut in it, of exactly the width of the shank 
 of the holder, and of slightly greater depth. This was 
 drilled across the groove, the holes at each side being 
 made a loose fit on the steel pin. The tool-holder being 
 inserted in the groove of this block, and the pin driven 
 through, the tool-holder was free to rock on the pin as a 
 horizontal axis, but was prevented by the sides of the 
 groove from having any lateral motion relatively to the 
 block. The block and tool-holder thus connected were 
 placed in the tool-rest of a 14|- inches centre double- 
 geared lathe, and bolted down with the ordinary tool 
 clamping-plates. The tool-holder was still free to rock on 
 the pin through a small vertical arc, limited by the spaces 
 over and under the top and bottom of the shank and the 
 surfaces of the plates of the tool-rest. These latter 
 spaces were then filled up by two small steel plates filed 
 accurately parallel, and to such a thickness that they 
 could be both slipped into their places at the same time. 
 
176 
 
 CUTTING TOOLS. 
 
 [Cbap. VII. 
 
 and could be moved easily to and fro, blit at the same 
 time prevented any vertical oscillation of tlie tool- 
 holder. 
 
 The back end of the tool-holder had two holes drilled 
 and tapped in its upper side, and by these there was 
 bolted to it a long iron bar. This bar was graduated in 
 suitable divisions, like a scale-beam, and heavy and light 
 weights were hung on it, by which the pressure brought 
 on the tool point was accurately balanced. A small 
 cranked bracket was fixed to the rest, so as to stand 
 over the scale-beam, and the unbalanced weight of the 
 scale-beam and tool-holder was suspended from this 
 bracket by means of a spiral spring that could be 
 screwed up to any tension and length. Before any 
 weights were hung on the beam, and without contact 
 between the tool and the work, but after the tool had 
 been placed in its right position in the tool-holder, this 
 spring was screwed up until the holder was floated 
 accurately in its horizontal position, the accuracy of 
 this adjustment being tested by feeling whether the 
 two small parallel steel plates moved to and fro with 
 equal ease. This adjustment was frequently tested 
 during the course of the experiments, and could be 
 made with great delicacy. 
 
 When an experimental cut was begun, before suf- 
 ficient weight was put on the beam to balance the 
 pressure the tool was held up to its work by the clamp- 
 ing-plate of the tool-rest, so that the pressure exerted 
 by it on the tool-holder kept the upper of the two loose 
 steel plates tight so that it could not be moved to and 
 fro. The heavy weight being adjusted on the bar to 
 balance the pressure approximately, a small weight 
 was then moved along the bar until this upper plate 
 just became loose. If the weight were moved beyond 
 its proper position, the lower “ feeling plate” became 
 tight. The weight was placed exactly so that the upper 
 and lower plates moved to and fro with equal ease. 
 With the very heavy cuts the trembling produced by 
 
PLATE X. 
 
 Steel . 
 
 Pig. 45 .— Curves co-ordinating the Cutting Forces exerted by .the Points of Turning Tools, with the Depths of 
 Shavings removed. Each Cu< ve is for one constant Width of Shaving, which is marked on the Curve in 
 Figures as the fraction of an inch. 
 
Chap. VII.] EXPERIMENTS ON CUTTING FORCE. 
 
 177 
 
 the pressure caused these plates to feel tighter than 
 when no cut was being taken, but after a little practice 
 it was always easy to set the weight so that the one 
 offered precisely the same amount of resistance to 
 motion as did the other. With loads on the tool point 
 up to about 200 lbs., a difference of 2 lbs. on the point 
 was easily felt by this means. With 600 or 700 lbs. the 
 possible error was not more than 3 lbs., and with the 
 greatest load used, namely 920 lbs., it was no more than 
 5 lbs. 
 
 17. Influence of Cutting Speed on Cutting Pressure. 
 
 — Each cut taken was taken at four different speeds, 
 ranging from the slowest speed of the lathe to the fastest 
 at which the lathe was capable of making the desired 
 cut. As some of the shavings taken off were heavier 
 than was suitable for the lathe, the highest speeds in 
 some of the experiments are considerably below what 
 would be practicable in a larger lathe under similar con- 
 ditions of work. 
 
 The speed at which the cast-iron was cut varied from 
 14 down to 2J feet per minute. Steel was turned at 
 speeds ranging from 6 to 1 - 3 feet per minute, and wrought- 
 iroivat from 9|- to 1-| feet per minute. 
 
 The pressure was measured in all cases at each speed. 
 The result showed that there is a slightly increased force 
 required for increased cutting speed, but that the in- 
 crease is very trifling. This increase is very curiously 
 constant for all conditions of cutting, for deep and 
 shallow cuts, for broad and narrow shavings, and for 
 all the three metals experimented upon. The increase 
 of force corresponding to the alteration from the 
 slowest to the fastest speed averaged about 25 lbs. 
 and ranged irregularly from 15 to 35 lbs. In one case 
 only was it as great as 401bs., and in two cases as small 
 as lOlbs. 
 
 18. Comparative Resistance to Cutting in Different 
 Metals. — The following examples will illustrate the dif- 
 ference between the three metals operated upon. 
 
 M 
 
178 
 
 CUTTING TOOLS. 
 
 [Chap. VII. 
 
 
 Number of 
 Experiment. 
 
 i 
 
 Pressure on 
 Tool point, 
 lbs. 
 
 Traverse 
 
 Feed. 
 
 Incb. 
 
 Cutting 
 Speed. Feet 
 per Min. 
 
 Depth of 
 Cut. 
 Inch. 
 
 O. I. . 
 
 mm 
 
 176 
 
 H | 
 
 13 
 
 
 W. I. 
 
 
 190 
 
 HUSH 
 
 9*6 
 
 
 Steel . 
 
 149 
 
 430 
 
 *0385 
 
 5*8 
 
 •04 
 
 0. I. . 
 
 69 
 
 252 
 
 mm 
 
 12*7 
 
 
 W. I. 
 
 213 
 
 470 
 
 Kiln 
 
 9-1 
 
 •06 
 
 Steel . 
 
 165 
 
 680 
 
 *0385 
 
 5’1 
 
 i 
 
 •06 
 
 These numbers show that while for both thin and mode- 
 rately thick shavings forged steel takes from 2 to 2J 
 times as much power to cut it as does cast-iron, wrouglit- 
 iron takes very little more than cast-iron for shallow 
 cuts, and rather more than 1 J times as much for cuts 
 of about Jq inch deep. In fact, for broad thin shavings 
 it was found that cast-iron required more cutting force 
 than wrought-iron. 
 
 19. Influence of Variation of Traverse Feed on 
 Cutting Pressure. — The variation of the pressure along 
 with the rate of feed per revolution — that is, with the 
 breadth of the shaving — is very decided. The annexed 
 table will show this. 
 
 It may be observed at once from this table that the 
 force on the tool does not increase in nearly so rapid a 
 ratio as the breadth of the shaving. There is the same 
 series of feeds in all the examples quoted in the table, 
 namely, *0303, -0385, 0555, and 0606. The last is 
 exactly double the first of the series. The ratios of the 
 last three to the first are 1*264, T833, and 2. The suc- 
 cessive differences are *0082, 0170, and *0051. The 
 ratio between the lowest and highest forces is generally 
 about 1^, although sometimes a little less, and in one 
 case considerably more, this latter being that of the 
 medium cut on steel. The second difference in the feeds 
 
PLATE XI 
 
 Wrought 
 
 Iron 
 
 Gun- 
 
 METAIi, 
 
 r*vrno / a j.i .. r»i. - . r \ 
 
 lift 
 
Chap, YII.] CUTTING FORCE IN LATHE-TURNING, 
 
 179 
 
 
 Number of 
 Experiment. 
 
 Pressure on 
 Tool point, 
 lbs. 
 
 Traverse 
 
 Feed. 
 
 Inch. 
 
 Cutting 
 Speed. Feet 
 per Min. 
 
 Depth of 
 Cut. 
 Inch. 
 
 
 65 
 
 228 
 
 Hi 
 
 IHH 
 
 •05 
 
 
 69 
 
 252 
 
 
 
 •05 
 
 • 
 
 Pi 
 
 73 
 
 288 
 
 •0555 
 
 
 •05 
 
 0 
 
 .a 
 
 1 
 
 77 
 
 340 
 
 •0606 
 
 HQB 
 
 *05 
 
 •+3 
 
 
 
 
 
 
 GO 
 
 c3 
 
 97 
 
 510 
 
 
 n-i 
 
 •135 
 
 o 
 
 101 
 
 620 
 
 
 ii-i 
 
 •135 
 
 
 105 
 
 690 
 
 •0555 
 
 ii-i 
 
 •135 
 
 
 109 
 
 775 
 
 •0606 
 
 n-i 
 
 •135 
 
 
 177 
 
 165 
 
 — 
 
 9-6 
 
 mm 
 
 
 181 
 
 190 
 
 
 9-6 
 
 
 
 185 
 
 215 
 
 •0555 
 
 9*6 
 
 
 
 189 
 
 250 
 
 •0606 
 
 9-6 
 
 
 ci 
 
 
 
 
 
 
 o 
 
 Pi 
 
 • rH 
 
 209 
 
 435 
 
 •0303 
 
 mam 
 
 •06 
 
 -p> 
 
 H 
 
 213 
 
 470 
 
 •0385 
 
 HS^B 
 
 •06 
 
 bD 
 
 r4 
 
 217 
 
 530 
 
 •0555 
 
 9-1 
 
 •06 
 
 P 
 
 O 
 
 £ 
 
 221 
 
 570 
 
 •0606 
 
 9-1 
 
 •06 
 
 £ 
 
 225 
 
 630 
 
 ■a 
 
 7*9 
 
 •14 
 
 
 229 
 
 760 
 
 ■SB 
 
 7-9 
 
 •14 
 
 
 233 
 
 810 
 
 •0555 
 
 7*9 
 
 •14 
 
 
 237 
 
 920 
 
 •0606 
 
 7*9 
 
 •14 
 
 
 m 
 
 185 
 
 HRfl 
 
 6 
 
 •02 
 
 
 
 215 
 
 
 6 
 
 •02 
 
 
 137 
 
 250 
 
 
 6 
 
 •02 
 
 
 141 
 
 315 
 
 HUH 
 
 6 
 
 •02 
 
 
 HRm 
 
 365 
 
 •0303 
 
 5*8 
 
 
 • 
 
 r“H 
 
 ■EH 
 
 430 
 
 •0385 
 
 5-8 
 
 ^Bf^H 
 
 O 
 
 <D 
 
 <4-3 
 
 153 
 
 480 
 
 •0555 
 
 6*8 
 
 
 m 
 
 157 
 
 665 - 
 
 •0606 
 
 5-8 
 
 ^B^^B 
 
 
 161 
 
 615 
 
 •0303 
 
 5-1 
 
 •06 
 
 
 165 
 
 680 
 
 •0385 
 
 5-1 
 
 •06 
 
 
 169 
 
 705 
 
 •0555 
 
 5*1 
 
 •06 
 
 
 173 
 
 810 
 
 « 
 
 •0606 
 
 5-1 
 
 •06 
 
180 
 
 CUTTING TOOLS. 
 
 [Chap. VII. 
 
 is double the first, but in no case does the corresponding 
 second difference in the forces nearly equal double the 
 first difference. The third difference of the feeds is less 
 than 4 the second, but in nearlv every case does the 
 third difference in the forces greatly exceed the second 
 difference. Thus the ratio between the increase of the 
 force and the increase of the feed at first diminishes, and 
 then again very rapidly increases. This is shown clearly 
 by the diagrams in Fig. 44. These curves form a com- 
 plete graphic record of the experiments on each of the 
 three materials, and are arranged specially to show the 
 variation of the cutting force with the breadth of shav- 
 ing. The force in pounds is measured horizontally from 
 the left-hand side of the diagram to the scale marked on 
 the edge. The corresponding breadth of shaving — that 
 is, the parallel feed per revolution — is measured vertically 
 upwards, the scale being marked along the side of the 
 diagram. All the curves are shaped more or less like an 
 S. They first bend upwards, and then bend with an 
 opposite curvature. 
 
 20. Influence of Variation of Depth of Cut on Cut- 
 ting Pressure. — The same table will illustrate the mode of 
 variation of the cutting force with the thickness of the 
 shaving. This would be more clearly exhibited by a 
 fuller extract from the original record of the experiments, 
 but space will not allow of the insertion of more. It is, 
 however, still better represented to the eye by the curves 
 drawn in Fig. 45, which are plotted from the same results 
 as those shown in Fig. 44, but are so arranged as to show 
 directly the relation between the depth of cut and the 
 pressure on the tool. The pressure is here measured 
 horizontally, as in Fig. 44, and to the same scale. The 
 depth of cut is measured vertically to the scale marked 
 at the side of the figure. The law of variation is exactly 
 the converse of that in Fig. 44. At first the pressure 
 increases at a more rapid rate than the depth, and then 
 the rate of increase gradually falls off, until it becomes 
 less than that of the depth. The curves are, therefore, 
 
PLATE XII. 
 
 Fig 45b. — WEOU GrHT-IRON SHAYINGr. (After a Photograph.) 
 
Chap. VIII.] 
 
 PHOTOGRAPHS OF TURNINGS. 
 
 181 
 
 S-shaped once more, but the direction of the two bends 
 is reversed from those seen in Fig. 44. 
 
 The sum of the breadth and depth of the shaving is 
 approximately equal to the length of the portion of the 
 cutting edge of the tool that is in action — that is, the 
 length of cut being taken at each instant. From an 
 examination of the curves, it is seen at once that the 
 force does not vary in simple proportion to this quantity, 
 nor in proportion to any single constant power of it. 
 
 SI. Photographs of Shavings of Cast-iron, Wrought- 
 iron, Steel, and Gun-metal. — Fig. 46, a and b, shows a 
 series of photographs taken from lathe shavings. In the 
 first series the material is cast-iron ; that of the second is 
 wrought-iron ; that of the third, steel; and that of the 
 fourth, gun-metal. They show well the manner in which 
 the cutting forces break up the shavings in layers, and 
 show also the marked differences that exist between the 
 different metals in this respect. Fig. 46, B, is a large- 
 sized shaving of wrought-iron. 
 
 CHAPTER VIII. 
 
 BORING AND DRILLING. 
 
 1. Boring and Turning. — There is a'distinction made 
 in technical language between the turning of outside and 
 that of inside surfaces. The latter is called boring. 
 
 The differences between boring and outside turning 
 all result from the contracted character and peculiar 
 position of the space in which the boring tool must be 
 held. 
 
 If the diameter of the inside surface being bored is 
 large, then the conditions under which the shaving is cut 
 and broken off are the same as for a plane surface. The 
 tool edge stands at the level of the centre, and the direc- 
 tion of the surface on which it operates is vertical at the 
 
182 
 
 CUTTING TOOLS. 
 
 [Chap. Vlir. 
 
 cutting edge. If the diameter be large, the small quantity 
 of metal lying on the surface immediately above the tool 
 point, through which the pressure exerted by that point 
 is distributed and which is severely crushed and twisted, 
 stands to a very close degree of approximation accurately 
 vertical. If, however, the diameter be small and the 
 crushing pressure be supposed to penetrate upwards the 
 same distance as in the previous case before it becomes 
 dissipated in breaking the shaving, it is evident that 
 this small length of surface is no longer accurately 
 vertical. At its lower end it is vertical, but at its upper 
 end it leans inwards towards the centre so as to make an 
 angle less than 90° with the horizontal diameter. Com- 
 
 o 1 
 
 paring pieces of different small diameters, and always 
 taking the same small depth of crushed material in all 
 of them, clearly the average inclination from the vertical 
 will be greater the less is the size of the hole. Now, this 
 lessening of the angle between the metal affected by the 
 tool pressure and the horizontal diameter is evidently 
 equivalent to a lessening of the angle of top-rake of the 
 tool, and results in greater difficulty of cutting in small 
 holes than in large ones, the shape and position of the 
 tool point being supposed the same in the different cases. 
 This difficulty cannot be overcome by setting the edge of 
 the tool a little lower than the centre, because if this be 
 done a greater amount of bottom-rake must be given to 
 the tool, in consequence of the inclination of the surface 
 to which the point would be applied. This bottom-rake 
 is, as has been already explained, made as small as it may 
 be consistently with preventing pressure on the surface 
 under the point of the tool, and thus the above increase 
 of it would be quite necessary. This would lessen the 
 cutting angle below its proper value and thus weaken the 
 edge. 
 
 The tool is, therefore, maintained at the exact level 
 of the centre, and in consequence of the above difficulty 
 it should be given a little more top-rake than the ordinary 
 outside turning tool. The cutting angle thus becoming 
 
Chap. VIII.] 
 
 FACE-PLATE BORING. 
 
 183 
 
 keener and weaker, it is impossible to take such heavy 
 cuts in boring small holes as those taken in outside 
 turning. 
 
 Again, when the hole is small the surface of the work 
 underneath the tool rapidly bends towards the tool, so 
 that if the tool be not of very small depth or given 
 excessive bottom-rake, its lower face must be ground- 
 curved, so as not to catch the side of the hole at its lower 
 edge. This rounding off of the bottom corner of the tool 
 does not in the least affect its cutting action, and does 
 not materially lessen its strength. 
 
 2 . Difficulty of Supporting the Tool in Face-plate 
 Boring. — We here go on the supposition that the work 
 is rotated and the tool held fixed. This is not always 
 the case, as will be mentioned immediately ; but if it is 
 so, the rest upon which the tool is fixed cannot stand 
 opposite to it, i.e., in the same plane perpendicular to 
 the centre-line of the lathe as the tool. The lower part 
 of the rotating work interferes with the possibility of 
 any straight vertical support from the tool down to the 
 lathe bed. The tool must, therefore, be held in a tool- 
 h older clamped horizontally in the slide-rest and parallel 
 to the line of centres. This projects into the hole. If 
 the hole be a deep one, the bar tool-holder must be 
 correspondingly long ; and, in consequence of the “ over- 
 hang,” it is projiortionately difficult to hold the tool 
 perfectly steady and to prevent it springing. The bar 
 must, therefore, be made as stiff as possible. When the 
 hole is small, there is often difficulty in getting room 
 enough for a bar of sufficient stiffness. This over- hang 
 of the holder is another circumstance preventing heavy 
 cuts being taken in boring small diameters, the jarring of 
 the tool with a heavy cut preventing it cutting truly and 
 rendering breakage of the edge easy. 
 
 The point of the tool must, as in turning, be shaped 
 suitably for the work to be done. A round nose with 
 side-rake is the best for roughing-out. If a sharp inside 
 corner lias to be bored out, the tool must have a corre- 
 
184 
 
 CUTTING TOOLS. 
 
 [Chap VIII 
 
 spondingly sharp-angled point. The tool is best made of 
 a small piece of steel wedged into a bar-holder, but 
 boring tools for small work are frequently made with 
 the point solid in one piece with the shank, the shank 
 being of tool-steel and having its end forged to a crank 
 shape so that the cutting edge stands out to the left- 
 hand side of the bar. 
 
 3. Boring Bar. — When the work is of large size it 
 is much more convenient to give the rotational move- 
 ment to the tool than to the work. This is the ar- 
 rangement in the majority of boring operations. The 
 tool, a small piece of steely is fixed to a long bar, 
 termed a u boring bar” which is placed between the 
 lathe-centres and driven by a carrier and driver as 
 if it were a piece to be turned in the usual manner. 
 The work is fixed on a table that slides along the bed 
 exactly as does the ordinary slide-rest. This table 
 may have parallel under-cut grooves in its surface 
 for the insertion of T-headed bolts by means of which 
 the work is clamped in place. The feed motion is 
 given to the table and the work upon it by a leading 
 screw or a rack and pinion. Such boring is fre- 
 quently done in an ordinary lathe when the saddle of 
 the slide-rest is used as a table to which to fix the work. 
 In workshops where much of such boring has to be done 
 there are always some lathes specially constructed for 
 this class of work. These are called boring lathes , or 
 “ boring machines.” The chief peculiarity of these 
 lathes is that the centres stand at a great height from 
 the bed in order that large-sized work may be admitted, 
 and that no provision is made for the attachment to the 
 mandril of face-plates or jaw-chucks. The boring bar is 
 very commonly coupled to the mandril by a split cone 
 coupling. 
 
 The small boring tool ought to be well supported at 
 no great distance from its point. Tor holes under four 
 or five inches the bar may be made of large enough 
 diameter for the tool to have a bearing at its outer 
 
Chap. VIII.] 
 
 BORING BARS. 
 
 185 
 
 surface, sufficiently near the edge. For medium- sized 
 holes there may be placed on the bar a thick strong 
 cylindrical plate like a piston, in the circumference of 
 which the tool is inserted in a hole. Such a holder is 
 convenient as it may be shifted along the bar to any 
 position suitable for the work. It may also have 
 several tools placed at different points on its circum- 
 ference on a spiral line (one tool being axially a small 
 distance in advance of the next). This allows of a 
 correspondingly quicker feed being given to the work, 
 and also equalises the cutting pressure in different 
 directions, so that there is very little tendency for 
 either the work or the boring-bar to spring. At the 
 same time, however, it must be noticed that if the 
 different tools are not set so that all their cutting edges 
 are precisely equi-distant from the axis of the bar, the 
 bored surface will be found with a number of spiral 
 grooves of small depth cut in it. To set the tools so 
 accurately as to avoid this result perfectly is somewhat 
 troublesome, and if several cuts have to be taken off the 
 surface a new setting of the tools is required for each. 
 
 When the hole to be bored is several feet in diameter, 
 a strong cross-beam of iron is firmly attached to the 
 boring-bar, and on the end of this beam is mounted 
 the holder in which the tool is inserted. 
 
 4. Boring Large Cylinders. — Large cylinders, when 
 their walls are not very thick, are so heavy that 
 when lying on their sides they bend slightly out of 
 the true cylindrical shape. It then becomes difficult 
 or impossible to bore them out truly in that position. 
 Cylinders over six or seven feet in diameter are, 
 therefore, much better held vertically when being 
 bored. The boring-bar is placed upright, its journals 
 revolving in bearings in stiff iron beams, supported 
 in the walls of the workshop. It would in this case 
 be inconvenient to give a vertical feed-motion to so heavy 
 a piece of work, and the boring bar is given a slow 
 upward or downward motion simultaneously with its 
 
186 
 
 CUTTING TOOLS. 
 
 fClmp. VI tt. 
 
 rotation , tlie tool point thus following a spiral path of 
 small pitch. 
 
 5. Double-boring Machines. — There are frequently 
 two cylinders to be bored parallel to each other in the 
 same casting, as, for instance, in double cylinder engines 
 of small size. Then if the two cylinders of a double 
 cylinder engine are cast in two separate pieces, it is well 
 first to plane and fit together the surfaces by which the 
 two are to be joined and bolt them together, and after 
 this is done, to bore them. It is thus easier to ensure 
 accurate parallelism between the cylinders. For such 
 work an extremely convenient boring machine is con- 
 structed with two boring bars driven simultaneously at 
 the same rate, the two being connected by a cross shaft 
 and bevel gearing. The two bars may be drawn apart so 
 as to stand at any exact required distance from each 
 other, this distance being that desired between the centres 
 of the cylinders. The gearing between the two must 
 then be adjustable. 
 
 In such a double boring machine it is better that the 
 two tools should revolve in opposite directions, because 
 then at each instant the horizontal components of the two 
 cutting thrusts will balance each other, and there will be 
 the less tendency towards shifting of the work by the 
 loosening of the bolts holding it down to the slide-carriage. 
 
 6. Drilling and Boring. — Drilling is another method 
 of forming inside cylindrical surfaces. • Like boring, 
 drilling may be performed either vertically or horizon- 
 tally. The former is the common direction in which 
 drilling machines act. Horizontal drilling is not unfre- 
 quently done in the lathe, the drill being fixed in a 
 chuck and rotated with the mandril, while the work is 
 fed up against it by being pressed by the centre in the 
 poppet-head. 
 
 In drilling, the rotational motion is invariably given 
 to the tool (the method being adapted for holes of small 
 size), and the feed-motion is usually, but not always, 
 given also to the tool. 
 
e/mp. yin.] 
 
 DRILLING AND BORING. 
 
 187 
 
 As the words are ordinarily understood, there are two 
 characteristic distinctions between drilling and boring. 
 In the latter operation the hole is already roughly made 
 in. casting or in forging the piece, and the cutting tool 
 has only to reduce the irregularities of the surface and 
 to make the hole of the exact required diameter, it being 
 left in the rough somewhat smaller than its finished size. 
 In drilling, on the other hand, the hole is cut out of a 
 solid piece, so that the material removed in the shape of 
 shavings corresponds to the full volume of the hole. In 
 the second place, in boring the tool operates on a cylin- 
 drical surface only, which is parallel to the axis of 
 rotation, while a drilling tool acts chiefly, and almost 
 solely, upon a flat or conical surface which lies 'across the 
 axis of rotation. Another distinction may be found in 
 the fact that while drills have always two cutting edges 
 acting on opposite sides of the axis, a boring-tool has 
 ordinarily only one which cuts at each instant on one 
 side alone of the hole. A further important difference 
 lies in the modes of guidance, as will be apparent from 
 what follows in section 9. 
 
 7. Drilling Tools : Defects of Ordinary Forms. — 
 Fig. 49 (Plate XIII. ) shows a common form of drilling 
 machine. A horizontal driving shaft rotates the vertical 
 spindle h by means of the pair of mitre wheels g and h. 
 To this spindle the drill is fixed in the socket and, 
 the work being fixed on the table v> the spindle is fed 
 downwards as the hole is drilled deeper. 
 
 The drill is a straight piece of round steel, shaped 
 suitably at its lower end to perform its work of cutting 
 out the bottom of the hole. Various forms are illustrated 
 in Fig. 47. The commonest, because the most easily 
 made, is represented by a. The shank is forged out to a 
 flat blade, which is usually made a little wider at its 
 lower extremity than above it. The bottom, edge is 
 diamond-shaped, the two sides being equally inclined to 
 the horizontal by an angle that, among drills for different 
 purposes, varies from 50° to 30°, the most common being 
 
188 
 
 CUTTING TOOLS. 
 
 [Chap. VIII. 
 
 between 40° and 50°. These two inclined edges are the 
 cutting edges, and are bevelled so as to prevent their 
 narrow flat faces rubbing against the conical cut surface 
 of the metal operated on — that is, so as to give a small 
 “ angle of relief.’ 7 The rotation given to the drill is 
 
 always right-handed, looking 
 towards the work. The two 
 cutting edges are, of course, on 
 opposite sides of the flat blade, 
 and the bevels, or back-rakes, 
 
 a 
 
 Flat-pointed. Flat point, with. Morse Cutter Pin Drill. 
 
 twisted edges. Twist Drill. 
 
 Fig. 47. — Drills for Metal. 
 
 given to them are correspondingly ground in opposite di- 
 rections. With a straight flat blade, it is impossible to give 
 any front-rake to the edges, as the faces must stand verti- 
 cally. In fact, if the thickness of the blade is made, as is 
 usual, somewhat thinner at the point than higher up, these 
 faces lean slightly towards the horizontal, and the rake 
 becomes negative. The same result — namely, negative 
 
Chap. VIII.] 
 
 DEFECTS OF COMMON DRILL. 
 
 189 
 
 rake — is further produced by the fact that the edge must 
 necessarily be not in a radial plane, but in a plane 
 passing to one side of the centre by half the thickness 
 of the blade. The size of the hole, and, therefore, the 
 radius to which the surface of the work is curved, being 
 small, this half-thickness represents a not inconsiderable 
 angle, and this difficulty effectually prevents the cutting 
 edge being formed favourably for good cutting. This 
 kind of drill is, therefore, perhaps, the most defective of 
 all cutting tools as regards the relation of the requisite 
 driving power to the amount of material removed. The 
 defect increases in magnitude the larger is the ratio of 
 the thickness of the blade to the diameter of the hole, 
 and it is thus greater in drills for small holes, because 
 it is practically impossible to reduce the thickness of the 
 blade in proportion to its width. 
 
 There is still another defect in this drill. Since the 
 two cutting edges already referred to pass at a small 
 distance from the centre of the hole and from each other, 
 there is left a small central core of metal that is never 
 touched by them, and cannot, therefore, be cut out by 
 them. Supposing the centre of the blade to lie accurately 
 in the centre of the hole, the diameter of this central 
 core equals the thickness of the blade. It is actually 
 cut away by the short edge that crosses from one face 
 to the other at the point of the blade, this edge being the 
 intersection of the two narrow surfaces lying behind the 
 main cutting edges and to which the back-rake has 
 been given. The line of this short edge is perpendicular 
 to the axis of the drill, and the surface it cuts is, there- 
 fore, not conical, like the rest of the bottom of the hole 
 but flat and also at right angles to this axis. If the side 
 edges be ground at 45° to the axis, the cutting angle of 
 this short edge is 90°, and it is situated very unfavour- 
 ably for cutting because the two faces intersecting in the 
 edge are equally inclined to the surface cut. The 
 front-rake is negatived by the large angle 45°, and 
 the back rake is also 45 Q , an angle that is for this 
 
190 
 
 CUTTING TOOLS. 
 
 [Chap. Y1TI. 
 
 purpose very unnecessarily large. To cut at all with 
 so badly-formed an edge, it is necessary to force the 
 edge downwards into the metal with great pressure, 
 and the removal of the material takes place more by 
 bruising and abrasion (by what has often been called 
 scraping) than by clean cutting. It is thus evident 
 that the severest duty performed by the drill is thrown 
 upon the point of the diamond, and it is found in prac- 
 tice that this part of the edge gets most frequently and 
 rapidly blunt. 
 
 This last defect may be to a great extent remedied 
 by grinding or filing a small half-round groove on the 
 opposite faces of the blade to the right and left hand 
 side of the point edge, as is illustrated in Fig. 48. Here 
 
 the main cutting edges 
 are d e and c h; the 
 cutting edge of the 
 central core is c e. 
 The two halves of this 
 edge at c and e cut 
 simultaneously in op- 
 a posite directions — the 
 half at c cutting to 
 the right-hand, and 
 that at e to the left- 
 Fig. 48 . hand, in the position 
 
 shown in the diagram. 
 To the left-hand of e and to the right-hand of c are filed 
 two small notches, extending with a gradually diminishing 
 depth a short distance up the respective faces of the 
 blade. The effect of these notches is to make the front 
 faces of the cutting edge c e perpendicular, or nearly 
 so, to the metal they cut. At the same time they 
 somewhat weaken the central portions of the edges d e 
 and c h. 
 
 8. Twisted Drills; Morse Twist Drills. — In this 
 common form of drill the cutting faces are inclined 
 by less than 90° to the surface of the work in front 
 
Chap. VIII.] 
 
 MOUSE TWIST DRILL. 
 
 191 
 
 of them. This angle ought to be much more than 
 90°; for wrought-iron it ought to be about 117°. This 
 inclination might be attained by bending forwards the 
 two edges in opposite directions when the tool is being 
 forged. Doing so would prevent the possibility of re- 
 grinding the edges many times without re-forging the tool; 
 it would make the proper grinding of the tool a diffi- 
 cult matter even the first time ; and the bending at the 
 forge would so weaken the material that the drill would 
 most probably be unable to stand any but the lightest 
 work. The end of the drill treated in this fashion 
 would have a twisted shape, as shown in (gl) Fig. *47. 
 The above objections are wholly obviated by making 
 the twist continuous for some distance up the shank. 
 This is what is done in the Morse twist drill, 
 shown in b, Fig. 47. The blade is made thick and 
 strong, and is carefully and accurately cut by 
 machinery to the form of a double -threaded spiral. The 
 inclination of the spiral to the axis is the front-rake of 
 the tool. As the tool point is re-ground farther and 
 farther back, the two cutting faces are always found at 
 the same inclination. An extra advantage is that the 
 shavings being pressed against the sides of the hole and 
 suffering from this contact frictional resistance to being 
 carried round with the rotation of the drill, are forced to 
 slide up the two grooves of the spiral, and the hole is 
 thus easily kept clear of the metal cut away. With tho 
 ordinary drill the difficulty of getting out the shavings is 
 a great hindrance to the work, especially with cast-iron. 
 On these accounts the Morse drills are decidedly the 
 best that can be used, even although in first cost they are 
 considerably more expensive than those of the ordinary 
 shape. They do not, however, alter the inefficient 
 character of the short edge lying cross-wise between the 
 faces and by which the central core is scraped out. In 
 this respect the Morse is slightly worse than the other 
 because of the increased thickness and consequent in- 
 creased length of the cross-edge, whereby the diameter 
 
192 
 
 CUTTING TOOLS. 
 
 [Chap. YIIJ 
 
 of the central core is left larger. The other advantages, 
 however, greatly outweigh this disadvantage, which may 
 probably to some extent be overcome by notching the 
 back edges in the way described in the last section. In 
 the Morse, the file, however, could not be nsed for making 
 such notches because its use would involve softening 
 the steel in the fire, and it would be a little difficult to 
 grind them satisfactorily. * 
 
 9. Guidance of Drilling Point: Centring. — The 
 
 guidance of these pointed drills is such as not to be 
 rigidly exact, and therefore requires careful manipu- 
 lation. Suppose the drill has already penetrated a 
 short distance into the material so that the top of the 
 cutting edges is below the surface ; a portion of the 
 parallel walls of the hole has already been formed, and 
 against these bear the vertical parallel edges of the blade 
 of the tool ; these edges are narrow, and do not present 
 a good bearing surface. So far as they do give lateral 
 support to the drill, they tend to maintain its axis from 
 instant to instant during its downward motion in the 
 same exact line as that which it occupies at each instant, 
 which line is determined at each such time by the precise 
 position of the lower end of the drill and by that of the 
 socket at the bottom of the spindle in which the shank 
 of the tool is inserted. The line in which this socket is 
 fed downwards is the vertical centre line of the spindle, 
 and if the bottom end of the tool be not accurately in 
 the same line, then the cenfcre-line from top to bottom of 
 the drill will change continuously during the downward 
 feed, always departing more and more from the vertical, 
 this being possible because the shank is not held perfectly 
 rigidly in the socket. The consequence is that the 
 cutting end of the drill follows a curved line, the curve 
 being modified and made flatter than it would otherwise 
 be by the guiding resistance of the vertical edges of the 
 
 * A special grinding machine for the point edges of twist drills has 
 recently come into use. It ensures the edges being formed with exact 
 symmetry, and accurately to the correct angles. 
 
Cliap. VIII.] 
 
 GUIDANCE OF DRILLS. 
 
 103 
 
 blade bearing against the walls of the hole. But these 
 latter edges are sharp enough to cut in an imperfect way, 
 and the effect of the above action is that they cut away 
 the walls of the hole on one side, leaving it of an oval 
 section. In the Morse dril] the lateral edges are made 
 truly cylindrical and are much broader than in ordinary 
 flat drills, so that they give much more effective guiding 
 support to the tool and cause less risk of ovalness. 
 
 Erom the above may be seen the great importance of 
 ensuring that in beginning the hole the drill should “ run 
 true,” that is, that the centre of its lower end should lie 
 accurately in the continuation of the centre line of the 
 spindle. The centre here spoken of is the centre of the 
 width from edge to edge. It will appear from what 
 follows that the extreme point of the cutting end must 
 coincide accurately with this centre, and that this point, 
 therefore, must “ run true,” so as to appear motionless 
 during the revolution of the drill. 
 
 The pressure against the conical surface at the bottom 
 of the hole is much greater than that at the sides. The 
 latter may be called accidental, and is practically nil 
 when the hole has been started fairly and is fed down 
 truly in the centre line. The former is the cutting 
 pressure of the two edges. It has a vertical component 
 equal to the force exerted in applying the feed. The 
 horizontal part of the force on each cutting edge may be 
 divided into two parts, one perpendicular to and the 
 other along a radius of the cone. The radial components 
 at the two opposite edges are oppositely directed, and 
 push the drill oppositely, each towards the centre. If 
 these are exactly equal in magnitude, the point of the 
 drill is maintained in balance, and there is no tendency 
 to push it out of the straight line along which it is fed. 
 If, however, the one radial force is at any moment 
 greater than the other, the point is pushed in that 
 direction and its progress downwards becomes curved. 
 Such inequality in the two pressures may arise either 
 because of want of uniformity in the surface being cut — ■ 
 N 
 
194 
 
 CUTTING TOOLS. 
 
 [Chap. VIII. 
 
 for instance, because of a liole in tlie surface on one side, 
 or because of there being on one side a patch of harder 
 metal than on the other — or because of want of symmetry 
 between the two edges of the tool. If the want of 
 balance is produced by the first cause, the excess of force 
 is always in one direction across the hole, depending on 
 the location of the hole or patch of hard metal, and it 
 continues until the metal in which these are situated is 
 all cut away in the form of shavings. 
 
 Advantage of this is taken in centring the hole 
 when commencing it. A circle is drawn round the desired 
 centre, and larger by about inch than the hole to be 
 bored. “ Centre dabs ” are put upon this circle, because 
 the line is generally obliterated by the dust, sometimes 
 mixed with oil, which is caused by the drilling. Four 
 “ dabs ” are quite sufficient for holes up to inch in 
 diameter, and it is for very large holes only that more 
 than six are needed. Another dab is put in the centre, 
 and this one ought to be at least as wide as the thickness 
 of the point of the drill, so that this point may enter it 
 and be steadied by it. When between half and three- 
 quarters of the length of the cutting edges has entered the 
 metal, the drill is withdrawn, and the shavings or dust 
 blown or wiped aside ; the conical hole will then be found 
 nearly always to be not quite concentric with the circle as 
 indicated by the dabs. A narrow, round-nosed chisel, called 
 a “ centring chisel,” is then used to cut a groove on that 
 side of the cone towards which it requires to be “drawn” 
 in order to become concentric with the circle. The drill 
 is then fed down again a very short distance, and when 
 it has cut to the bottom of the groove made with the 
 chisel, it is once more raised and the hole examined. 
 The depth of the groove should be made larger the more 
 the hole requires to be “ drawn,” and if its size has been 
 skilfully proportioned in this way, there will be no occa- 
 sion to use the chisel a second time ; but if, on raising 
 the drill the second time, the hole is still found eccentric 
 from its true position, it must be drawn once more by 
 
Chap. VIII.] 
 
 GUIDANCE OF DRILLS. 
 
 195 
 
 using tlie chisel, and the operation must be repeated until 
 the hole has been moved to its exact right position. 
 
 It is to be noticed that it is only during the sinking 
 of the oblique cutting edges below the upper surface of 
 the work that this process is possible. As soon as the 
 parallel walls of the hole have been commenced, the effect 
 of the chiselled groove becomes very small, in conse- 
 quence of the guidance afforded by these vertical walls to 
 the sides of the drill. Care must therefore be taken to 
 finish the centring operation before the cutting edges 
 have wholly entered. If, when they have penetrated 
 nearly up to their upper ends, the hole is still found 
 considerably eccentric, the whole of that side of the 
 conical hole towards which the point is to be moved must 
 be chiselled away, so that the drill may be rapidly drawn 
 over. The chiselled groove is a great deal more effective 
 if made close down at the point of the cone than if 
 made high up on its side, because near the point a groove 
 of a given width means the cutting away of a much 
 larger proportion of the whole circumference than higher 
 up where the diameter is larger, and consequently means 
 that the inequality of pressure on the two sides of the 
 point is maintained during a much larger fraction of the 
 whole revolution of the drill. 
 
 If the inequality of pressure be due, not to irregularity 
 in the conical surface on which the drill presses, but to 
 want of symmetry in the drill itself, there are three 
 cases that may arise. The two edges may be both ground 
 at exactly the same angle to the axis, but the point where 
 they meet may be nearer one side of the blade than the 
 other, so that one cutting edge is longer than the other. 
 In this case the drill will be guided wholly by the point, 
 and a hole larger in diameter than the breadth of the 
 blade — of, in fact, a radius corresponding to the longer of 
 the two cutting edges — will be formed. A second kind 
 of dis-symmetry occurs when, the point being precisely 
 equi-distant from the two vertical sides of the blade, the 
 cutting edges are ground at different inclinations to the 
 
196 
 
 CUTTING TOOLS. 
 
 [Chap. VIII. 
 
 horizontal. When this is so, that edge with the greater 
 horizontal inclination never comes in contact with the 
 metal, and consequently the point of the drill is continu- 
 ally being pushed with great force towards this non-cut- 
 ting edge. The direction of this push is continually 
 rotating, and, therefore, the result is not to draw -the 
 hole in any one direction but to cause the drill axis to 
 rotate round a conical surface of small angle and the 
 point, therefore, to cut out a flat circular surface perpen- 
 dicular to the axis of a slightly larger diameter than the 
 thickness of the drill. The hole will thus be bored to a 
 somewhat larger diameter than the size of the hole, and 
 it is also evident that the motion will be unsteady and the 
 diameter of the bore not accurately constant. 
 
 When the two faults above mentioned are combined, 
 the inclinations of the two edges being unequal and also 
 the point being eccentric, the motion of the drill is still 
 more unsteady and the result still more unsatisfactory. 
 
 All the remarks of this paragraph apply to Morse 
 twist drills as well as to flat drills. In the former the 
 guiding influence of the walls of the hole after the cut- 
 ting edges have sunk below the surface is greater, and 
 that of the cutting edges less, than in the latter. 
 
 10, Other Forms of Drills for Metal. — In Fig. 47 
 c shows a third kind of drill, called a pin-drill. Its use 
 is The formation of flat counter-sinks, in which the heads 
 of bolts or of flat-headed screws may lie. The hole for 
 the body of the bolt being bored, the projecting central 
 plug of the drill enters this, its size being such as to be 
 an easy fit in the hole. Behind the plug, or pin, stand 
 two wing cutting edges perpendicular to the axis of the 
 hole. For each size of bolt a separate drill is required, 
 the ratio of the diameter over the extremities of the 
 cutting wings to that of the central pin being slightly 
 larger than the ratio of the size over the angles of the 
 nut to the diameter of the screw. 
 
 In d is illustrated a very similar tool, also used in 
 the drilling machine. The wing cutting edges here con- 
 
Cliap VIII.] LUBRICATION IN DRILLING. 197 
 
 sist of a loose cutter passed through a rectangular slot 
 near the lower end of a wrought-iron “ cutter bar/’ which 
 is fixed in the socket of the spindle. The cutter is held 
 tightly in the slot by a small wedge. 
 
 In these last two tools it is important that the two 
 edges should lie exactly in one horizontal plane. If they 
 do not do so, one of them will alone do all the work. In 
 the cutter bar, if the top and bottom of the slot be slightly 
 rounded, so that the cutter may be tilted through a small 
 angle without slackening the wedge, the pressure on the 
 cut surface will ensure that both edges cut equally. If 
 one lies lower than the other, it bears all the pressure, and, 
 there being none on the opposite end of the cutter, this 
 edge is pushed upwards until the pressures at the two 
 ends balance. The two edges should also be precisely 
 equally long. If the pin, or lower end of the bar, does 
 not quite fit the hole in which it runs, a piece of thin 
 sheet brass, or of brass tube split down otfe side, may be 
 put round it to make up the difference of sizes, and ensure 
 steadiness in the motion. 
 
 11. Lubrication in Drilling. — In drilling cast-iron 
 no lubricant of any kind is used, and brass is treated in 
 the same way. The shavings from these materials usually 
 break in minute fragments, which, if they were mixed 
 with a sticky liquid, would form a paste that would be 
 difficult to remove from the hole, which rapidly gets filled 
 up so that the rotation of the tool is impeded. As was 
 mentioned also in the chapter on lathes, these materials 
 are most easily cut “ dry,” independently of the difficulty 
 in getting rid of the shavings. Wrought-iron and steel, 
 on the other hand, must be drilled with a plentiful supply 
 of oil or soap and water. The writer does not know of 
 any authoritative explanation having been given of the 
 reasons why these materials require such different treat- 
 ment, but it seems probable that the difference arises 
 simply from the facts that a much larger amount of 
 power is required for the cutting of wrought-iron and 
 steel than for the others, and that most of the energy so 
 
198 
 
 CUTTING TOOLS. 
 
 [Chap. VIII. 
 
 expended is converted into heat, which is apt to overheat 
 the tools. This explanation is not entirely satisfactory, 
 however, because if one feels a drill after it has been 
 working on cast-iron for a few minutes, and then again 
 after it has been working the same length of time on 
 wrought-iron supplied to the usual extent with oil, he 
 will find that the drill point is much hotter in the former 
 than in the latter case. 
 
 12. Construction of Drilling Machines. — In Fig. 49 
 (Plate XIII ) the driving gear of the vertical spindle is 
 best seen in the section A. The driving belt runs on 
 the stepped cone-pulley b. This runs upon, but is 
 not keyed to, a horizontal shaft with bearings in the 
 standard. On the boss at the large end of the pulley is 
 keyed a pinion c, and behind this lies a toothed wheel, f t 
 keyed to the shaft. The pinion may be bolted to the 
 wheel, and when this is done the shaft is rotated at the 
 same rate as the pulley. There is also a side shaft, 
 corresponding to the back shaft of a lathe, on which are 
 mounted a wheel to gear with the pinion c and a pinion 
 to gear with the wheel f. These, being mounted on a 
 stud in an eccentric bearing, can be thrown forward into 
 gear or backward out of gear. When in gear, the bolt 
 fastening c to f must be slackened and pushed out of 
 the way-, and the shaft gets a reduced motion from the 
 pulley through the two pairs of pinions and wheels. 
 There being four steps to the cone, there are eight speeds 
 possible to the spindle. The vertical spindle is driven from 
 the horizontal shaft by a pair of bevel pinions, g and h, the 
 latter of which has a feather sliding in a key-slot in the 
 spindle, which is thus permitted to move up and down 
 without the driving connection being interfered with. 
 The work either rests loosely on, or is bolted to, the grooved 
 table v. This is a sliding table, having a nut, 7, bolted 
 to its under side, into which gears the screw $. By 
 turning this screw by a hand-crank set upon its squared 
 end, the upper table can be drawn farther or nearer the 
 standard. It rests upon a bracket, u. This is hinged to 
 
Chap. Yin.] 
 
 DRILLING MACHINES. 
 
 199 
 
 the vertical plate t by a strong hinge, the two bolts of 
 which are seen in the front view b. By swinging the 
 table ronnd this hinge, a motion is given to it transverse 
 to that given by the screw, and thus any number of 
 exact spots of a piece of work bolted on the table can be 
 successively brought under the drill and operated upon 
 without unbolting it. On the lower portion of the front 
 of the frame are two vertical slide surfaces, like those of 
 the bed of a lathe, and on these moves up and down the 
 plate t on which the hinge is made. It is clasped to the 
 vertical slides by the ordinary dove-tailed groove and 
 wings, with a triangular fitting strip at one side. In 
 bearings in the plate t lies a short horizontal shaft bear- 
 ing at its one end the pinion z, which gears with the rack 
 a that is bolted to the frame. By the rotation of the 
 pinion the table is thus lowered or raised. The short 
 shaft has at its outer end the worm-wheel y, actuated by 
 the worm x and the hand-wheel w. 
 
 13. Different Designs of Table. — Many other designs 
 are in common use for the purpose of giving the table 
 freedom to move under the drill in two horizontal 
 directions. One good arrangement is to use — in place 
 of the slide, nut, and screw of Fig. 49 — a circular table 
 swivelling round a large-sized vertical bolt in the hinged 
 bracket. The table, having been rotated into the desired 
 position, is clamped by a set-screw bearing on the side of 
 the bolt. 
 
 Again, instead of the vertical hinge in the plate £, the 
 standard frame of the machine is made with two legs, 
 the front one of which is in the form of a pillar. The 
 table bracket is then formed at its inner end as a 
 cylinder, and the cylinder embraces the pillar, so that the 
 table can swing round the latter : the pillar and cylinder 
 forming, in fact, a large-sized hinge. 
 
 The table is sometimes raised and lowered by means 
 of a screw and nut, but the rack and pinion are to be. 
 considered better. The rack should never form part of 
 the frame-casting, because its teeth are apt to be broken 
 
200 
 
 CUTTING TOOLS. 
 
 [Chap. VIII. 
 
 It should be a separate casting, fixed to the frame by 
 screws. It can then easily be removed and a new one 
 put in its place if it should get broken. 
 
 If the table be not clamped to the frame-slides by 
 bolts, the downward pressure of the drill, along with 
 the weights of the work and of the table itself, are apt 
 to cause- the rack-pinion to rotate slowly and allow the 
 table to sink. This may be perfectly avoided, however, 
 without the use of clamping-bolts, by the use of a pinion 
 of only two teeth. These teeth consist of two steel pins 
 projecting from the face of a small disc. This is keyed 
 to a shaft whose centre line lies in the plane of the pitch 
 lines of the teeth of the rack. When one pin-tooth lies 
 in a space between two teeth, the other tooth lies directly 
 underneath it in the space beneath. The line of pressure 
 on the faces of the teeth being thus vertical, and passing 
 through the centre line of the shaft, there is no ten- 
 dency to rotation in the two-toothed pinion, and there is 
 no risk of the table slipping downwards even when un- 
 damped. 
 
 14. Arrangement of Feed Gear. — The downward 
 feed of the spindle and drill-tool is given by the 
 hollow screw r. The pinion h is keyed to a long bush, 
 i, in which the spindle k slides, h being revolved 
 by a feather and slot. The bush i also encases the 
 lower part of the screw r, but this screw does not 
 rotate. Its lower end bears against a shoulder on the 
 spindle k, and part of the upward thrust of the spindle is 
 delivered to the screw by this shoulder. Above this 
 point the spindle is turned down to a smaller diameter 
 and passes upwards through the hollow screw to its top, 
 where a couple of lock-nuts form a collar covering the 
 upper end of the screw. The spindle can thus rotate 
 freely in the screw without carrying it round with itself, 
 but it must move up and down along with the screw. 
 On the top of this latter is screwed a cap, r 2 , through 
 which passes a steel set-screw, with a flat point bearing 
 against the upper end of the revolving spindle. This is 
 
PLATE XIH. 
 
 » 
 
 a, Sectional Elevation. b, Front View. 
 
 Fig. 49. — DOUBLE- GEARED DRILLING MACHINE. 
 
Cliap. VIII.] 
 
 DRILL FEED GEAR. 
 
 201 
 
 intended to take the main part of the feed-thrust, so as 
 to relieve the pressure on the shoulder lower down. 
 
 The screw r works in the long cast-iron bush r 1? which 
 is fixed in the frame. This bears a feather that enters 
 a longitudinal groove cut across the threads of the screw, 
 and so prevents the screw from turning, but permits its 
 vertical motion. In a bearing in the frame immediately 
 above this lies a nut, which can rotate, but is prevented 
 by collars from moving vertically. It forms the boss of 
 the wheel q, and the revolution of this wheel moves the 
 screw r, and with it the spindle k and the tool, up or 
 down as is desired ; q gears with the pinion p on the top 
 of the upright spindle e , seen in the front view, b. At 
 the lower end of this spindle is a hand-wheel by means 
 of which a hand-feed can be given to the drill. The 
 hand-wheel can be coupled to a worm-wheel that lies 
 immediately above it by a small cone-clutch, tightened up 
 by a screw and hand-nut underneath the .wheel. When 
 thus bound, the worm-wheel can drive the feed-spindle ; 
 otherwise it runs loose upon it. The worm-wheel, in its 
 turn, is driven by a worm n 9 and this is rotated by a nar- 
 row belt running over the small cone-pulleys l and m. 
 
 15. Other Arrangements of Feed Gear. — A great 
 variety of feed motions for drill-spindles has been invented. 
 That described above, although the most common, seems 
 by no means the best, involving as it does an unnecessarily 
 complicated construction. 
 
 It is easy to avoid any need of having the feed-screw 
 hollow. A rotating joint between its lower end and the 
 top of the spindle is easy to arrange so that the screw 
 may be able to lift the spindle as well as to press it 
 downwards. Fig. 50 shows one such arrangement, k 
 is the spindle, as in the previous figure, and r is the 
 feed-screw, which is now solid. The two bear against 
 each other on their flat ends at e, through which all the 
 feed pressure is delivered. To lift the spindle there is 
 the collar a screwed on the lower end of r, and kept in 
 place by the lock-nut b ; a is put over the reduced end 
 
202 
 
 CUTTING TOOLS, 
 
 [Chap. YIII. 
 
 of k , and two lock -nuts, c and d, screwed on the top of k 
 form a collar by which a can lift the spindle. For the 
 sake of compactness, c and d are made circular, and ar e 
 screwed up by a prong-key entering holes in their flat 
 
 surfaces, the lower one d being held 
 fast while c is tightened down on it 
 by a pin inserted in a hole in its 
 b peripheral surface and passed through 
 a hole in a from the outside. In 
 a putting the pieces together, a is first 
 put over Jc , d is then screwed down 
 to its proper position, which is such 
 as to allow a to revolve quite freely 
 round k, and then c is tightened down 
 on d. b is next screwed up to the top 
 of its run on r. Then a is screwed 
 on r until k is drawn to bear closely on the under surface 
 of r ; b is lastly screwed down again tight upon a. The 
 screw r is prevented from rotating by a feather fixed in 
 the frame-bearing. 
 
 Another plan consists in making the feed-screw in 
 one solid piece with the spindle. The nut is capable of 
 revolving in its bearing in the frame, being prevented 
 from vertical motion by collars. When it rotates at the 
 same rate as the spindle, the latter receives no feed 
 motion. If, however, the rotation of the nut be hindered 
 by the application of a frictional resistance to its motion, 
 the spindle moves in the nut, and receives a feed motion 
 proportional to the difference of rates of revolution of 
 the spindle and of the nut. The feed pressure being 
 transmitted through the thread of the screw to the nut, 
 this thread requires to be made square and strong to 
 withstand wear. Its pitch cannot, therefore, be a fine 
 one. Since the motion of the drill is a very rapid one, 
 and because of the largeness of the pitch of the screw, 
 the difference between the speed of rotation of the nut 
 and that of the screw-spindle must be very small in order 
 to give a slow feed motion. The feed pressure, after 
 
 Tig. 50. 
 
Chap. VIII.] 
 
 DRILL FEED GEAR. 
 
 203 
 
 being transmitted from the thread on the spindle to that 
 of the nut, is delivered by the nut through its collars to 
 the frame. There is thus a certain amount of frictional 
 resistance to the rotation of the screw inside the nut, and, 
 again, a certain amount resisting the rotation of the nut 
 in the hole in the frame. Supposing that the nut moves 
 with equal freedom on the screw and in its bearing in 
 the frame when no feed pressure is applied, then there 
 will be the same amount of friction caused at the collars 
 as at the threads of the nut, both being caused by the 
 same pressure — namely, the feed pressure. But the fric- 
 tion at the collars acts at a greater distance from the axis 
 than does that at the threads of the screw and has con- 
 sequently greater leverage to resist sliding motion. Thus, 
 if extra means were not adopted to prevent its being so, 
 the nut would always remain immovable in its bearing, 
 and the screw would revolve in the nut. This difficulty 
 can, however, be obviated by the simple expedient of 
 splitting the lower portion of the nut. The split portion 
 becomes slightly pliable, so that the two halves may be 
 drawn together by the application of a suitable force. 
 Being drawn together by two bolts, they are tightened 
 down on the screw, and thus cause an extra resistance to 
 the motion of the screw in the nut, independently of any 
 feed pressure. This ensures that the nut will rather 
 turn in its bearing than that the screw should turn in 
 the nut. To cause the screw to feed down through the 
 nut, extra frictional resistance must be applied to the 
 outside of the nut on a groove pulley cut on the nut for 
 that purpose, by a brake-collar or strap controlled by 
 hand. The rate of feed is proportional to the amount of 
 brake friction applied. On account of the rapidity of 
 the motion and the large pitch of the screw, the brake 
 friction must be applied delicately and with a reduced 
 leverage. To draw the drill upwards out of the work, 
 the nut must be made to revolve faster than the spindle. 
 This can be effected by means of four small bevel friction- 
 wheels or pinions. One of these three is cast in one piece 
 
204 
 
 CUTTING TOOLS. 
 
 [Chap. VIII. 
 
 with the nut at its upper end. A second is placed on 
 the screw, with the bevel downwards and at a higher 
 level than the nut, and is rotated by the screw, by means 
 of a feather in the pinion and a slot in the screw. This 
 pinion is prevented from shifting vertically by collar 
 bearings in an extension of the frame. The first pinion 
 is smaller than the second. They are thrown into gear 
 with each other by another pair of similar bevel friction- 
 wheels, cast in one piece and running on a horizontal stud. 
 One of these nearest the spindle is of the same size as 
 that on the top of the nut. The other, standing behind 
 it, is larger than the latter, but smaller than that rota- 
 ting along with the screw. These can be pushed back on 
 the stud away out of contact with the first pair, but when 
 they are advanced towards the screw they come simul- 
 taneously in gear with the first two mentioned, with the 
 desired result of the nut being driven faster than the 
 spindle, which is consequently raised with a rapidity 
 dependent on the ratio of the diameters of these bevel 
 pinions. * 
 
 One more feed arrangement may be briefly mentioned, 
 on account of its being frequently used. The upper part 
 of the feed-spindle is separate from the lower, and does 
 not rotate. On one side of it is cut a toothed rack. A 
 pinion gears with this, the rotation of which lifts or 
 lowers the spindle. A worm is keyed on the same 
 horizontal stud that carries the pinion, and a worm- 
 wheel gearing with the worm is carried at the top of a 
 vertical rod which is rotated by a hand- wheel fastened to 
 its lower end. An example of this gearing is seen in 
 Fig. 51. 
 
 16. Kadial Drilling Machine. — In the drilling 
 machine already described the line of the axis of the 
 drill-spindle is immovable, while different parts of the 
 work may be brought under it by moving the table. 
 When the piece to be drilled is very large and weighty 
 
 # The arrangement here described has not yet, at the date of 
 publication of this volume, been tried in practice. 
 
PLATE X1Y. 
 
 i 
 
 a, Side Elevation. 
 
 c, Section through Drill Spindle. 
 
 b, Vertical Section 
 
 Pig. 51.— RADIAL DRILLING MACHINE. 
 
Chap. VIII.] 
 
 RADIAL DRILLS. 
 
 205 
 
 it is more convenient to be able to move the drill- 
 spindle into different positions over the work. This is 
 accomplished in the radial drilling machine shown in 
 frig. 51. A heavy upright standard, «, seen in section b, 
 is firmly bolted to the foundation. In bearings in this 
 lies the shaft e, with a cone driving-pulley/, and at its 
 front a bevel pinion g. In front of the standard are 
 two vertical guide surfaces, on which slides a massive 
 hinge-plate b. This has a rack bolted to it by means 
 of which it can be elevated or lowered by the toothed 
 pinion m. The shaft upon which this pinion is mounted 
 is turned by a worm-wheel and worm, seen in the side 
 view A, the worm-shaft being rotated by a hand- wheel. 
 
 At the top and bottom of b are two large cylindrical 
 bearings, in which lies the large pin end of the canti-lever 
 gantry c. The whole of this projecting beam, or “ radial 
 arm/’ can thus be swung round these bearings, and the 
 drill, being mounted on it, is carried with it into any 
 desired radial position. Along guide surfaces on the 
 beam slides a plate d , seen in A and in the section c, 
 and on this an ordinary drill- spindle is mounted in the 
 manner the details of which are clearly shown in A. 
 Between the upper and lower hinge-pins the vertical 
 portion of c is shaped as a hollow half cylinder. In this 
 portion stands the shaft i. This is driven by the bevel- 
 wheel h , and it again by g. The shaft i is slotted 
 thruoghout the whole of its height, and slides upwards 
 or downwards with e through the boss of 4, in which 
 there is a feather fitting into the slot. The horizontal 
 part of the beam c is recessed in its front face between 
 the two slide surfaces, as seen in section c. In this 
 recess lies a screw, gearing into a nut fastened to d , and 
 moved by a hand- wheel p at the extremity of the arm. 
 By this screw the drill may be moved farther from or 
 nearer to the frame a . The bevel k at the top of the 
 shaft i drives a similar bevel on a short hollow bush. 
 This drives the telescopic shaft m n, on the end of which 
 is the pinion o, gearing with p on the drill-spindle. The 
 
206 
 
 CUTTING TOOLS. 
 
 [Chap. VIII 
 
 drill-spindle itself drives a pair of small bevels, which 
 actuate the feed-motion cones. The latter, by means of 
 the worm w on the same shaft, operates the shaft the 
 worm y, and the pinion a that gears into the rack /3, and 
 lifts it and the spindle along with it. 
 
 17. Multiple Drilling* Machine. — It is frequently 
 desired to drill a large number of holes with the centres 
 of all in one straight line. It saves much time if the 
 machine used has a number of parallel drill-spindles 
 which can all be brought into operation on the work 
 simultaneously. Such machines are called multiple drills. 
 The different drilling heads are all geared together by 
 being driven all from one horizontal shaft by means of 
 bevel-wheels. For general work they ought to be 
 capable of being shifted to different distances apart, to 
 suit the desired pitch of the series of holes. Frequently, 
 however, these multiple drills are constructed for a 
 special duty, in which the holes to be drilled are all 
 spaced alike, and in this case there is no need of being 
 able to adjust the drills relatively to each other. 
 
 18. Slot Drilling- -Slot drilling is a mode of making 
 key- way grooves in shafts, or similar recesses. The drill 
 has two straight edges perpendicular to the axis, so that 
 the bottom of the hole cut out is flat. The vertical side 
 edges are also made keen and sharp so as to cut easily. 
 The drill is sunk a small depth only underneath the sur- 
 face, and the work is then traversed horizontally under- 
 neath it, the side edges of the drill cutting out a longitu- 
 dinal groove. If the work be traversed in a straight line, 
 the groove cut is straight, and a circular or any other 
 groove may be cut by giving the work a corresponding 
 motion. The depth of cut being small, the operation has 
 to be repeated many times, the number of backward and 
 forward traverses made by the work being proportional to 
 the depth of groove desired. Slots for the insertion of keys 
 or feathers in shafts, and slots on shafts in which feathers 
 slide, are best cut out in this way. These slots are some- 
 times of very considerable length, and on that account 
 
Chap. VIII.] 
 
 SLOT DRILLING. 
 
 207 
 
 the sliding-table on which the work is bolted must be 
 long, and have a long range of motion. When the length 
 of the slot exceeds the possible travel of the table, one 
 portion of the slot is first finished, and the work then 
 
 Jig. 52.— a, Scotch Brace ; b, Geared Breast Brace 
 for Metal Drilling ; c, Nettlef old’s Squat 
 Ratchet Brace. 
 
 shifted and re-bolted to the table in a new position, care 
 being taken that the new position is in exact line with 
 the former one, so that the slot shall be continued pre- 
 cisely in the same line. 
 
 19. Hand Drilling in Wood and Metal; Hand Braces; 
 Ratchet Braces ; Bow Drill. — Metal is also often drilled 
 by hand, but, except for small sizes of hole, the process is 
 a tedious one because it is difficult to keep up by hand a 
 
208 
 
 GUTTING TOOLS. 
 
 [Chap. VIII. 
 
 sufficient speed of rotation to give the proper linear cutting 
 speed to the edges, this being so on account of the small 
 diameter of the mean circle on which the edge operates. 
 Hand-drills for metal are sometimes placed in braces of 
 
 Fig. 52. — d, Nettlefold’ s Ratchet Brace ; e, Nettlefold’s Swivel Brace. 
 
 the same construction as those used for wood. This is 
 shown in a of Fig. 52. The drill is clipped in a 
 socket by a spring catch in the lower end of the brace, 
 the middle portion is cranked and driven in rotation by 
 the right hand, and on the upper end is a loose semi- 
 spherical knob, by pressing against which with the breast 
 the drill is driven forwards. Such an instrument is 
 
Chap. VIII.] 
 
 RATCHET BRACES. 
 
 209 
 
 called a breast-brace. The knob is usually or wood, and 
 for work on wood the crank is also frequently made of 
 wood. Fig. 53 shows several wood drills, or “bitts,” as 
 they are technically termed, the forms of which are suffi- 
 ciently apparent from the illustration without further 
 description. In Fig. 52, b shows a breast-brace used 
 with metal drills. The bevel wheels are rotated by the 
 crank handle at one side, while the handle projecting on 
 
 w 
 
 Fig 
 
 the opposite side is used to steady the brace and prevent 
 its frame from turning round. In d (p. 208) is shown a 
 “ ratchet brace ” of the most common construction. This 
 is used in conjunction with a cramp, against an arm of 
 which (or sometimes against an overhanging portion of 
 the work) the steel centre at the top of the brace has its 
 bearing. This is upon a long nut, which is gradually 
 unscrewed from the screw which lies between it and the 
 lower portion of the tool. In proportion as the nut is 
 unscrewed the drill-point is fed downwards. The lower 
 cylindrical part rotates independently of the screw and of 
 the handle. The drill is fixed in the socket formed in 
 o 
 
210 
 
 CUTTING TOOLS. 
 
 ' [Chap. IN. 
 
 this part, and a ratchet-wheel engages with a spring 
 pawl upon the end of the handle. This handle is swung 
 backwards and forwards, with the result of giving the drill 
 a continuous slow rotation in one direction. Very many 
 designs for ratchet braces, in which one or other form of 
 automatic friction-clutch is substituted for the ratchet 
 wheel and spring pawl, have been patented. The illus- 
 tration, c, p. 207, shows what is called a “ squat” ratchet- 
 brace, the parts being so arranged that, while a fair range 
 of telescopic expanding motion is obtainable, the whole 
 length of the instrument is small, and it can be used in 
 confined spaces ; e , p. 208, illustrates another special form 
 of brace convenient for drilling in confined spaces. The 
 handle may be swivelled up or down. These patterns 
 are manufactured by Messrs. Nettlefold, of Birmingham. 
 
 The “ bow drill ” is a tool used by clock and small 
 instrument makers, and is suitable for very small holes 
 only. The cord of a bow is given a couple of turns 
 round a groove pulley mounted on the socket holding the 
 drill. By drawing the bow backwards and forwards, an 
 oscillatory rotation is supplied to the tool. 
 
 CHAPTER IX. 
 
 PUNCHING AND SHEARING MACHINES. 
 
 1. Similarity between Punching and Shearing. — 
 Shearing machines might well have been described in 
 an earlier portion of this w~ork, on account of the funda- 
 mental and simple character of the cutting action that 
 constitutes a shear. But in the series of tools that have 
 been already described, the sequence from chapter to 
 chapter, starting from the simplest tools in which the 
 other fundamental kind of cutting — namely, tearing — was 
 chiefly operative, has been so natural that no place has been 
 found before this to consider shearing pure and simple. 
 
 In the scientific sense of the word, shearing includes 
 
Chap. IX.] 
 
 PUNCHING! AND SHEARING. 
 
 211 
 
 j punching , In the two tools for shearing and punching 
 the cutting actions are of precisely the same sort. This 
 scientific connection finds curious expression in the fact 
 that the two tools are frequently, and indeed • usually, 
 combined in one. But they are quite as distinctly dif- 
 ferent machines, as, for instance, are a planing machine 
 and a turning lathe, in which also the cutting actions are 
 of the same sorb, and only different in so far as they are 
 
 Pig. 54, a. — Side Yiew of Punching and Shearing Machine. 
 
 affected by the shape of the work being formed. They 
 are more different than are planing, shaping, and slotting 
 machines. The difference between them is simply that 
 shearing machines, like planing machines, cut plane sur- 
 faces, while punching machines, like boring lathes, cut 
 inside cylindrical (or approximately cylindrical) surfaces. 
 
 The machines themselves will first be described, and 
 afterwards the cutting actions of the tools will be con- 
 sidered more minutely. 
 
 2. Combined Punching and Shearing Machine. 
 —This machine is shown in Fig. 54, A, b, and c. 
 The general arrangement is seen in the side and 
 
212 
 
 CUTTING TOOLS. 
 
 [Chap. IX. 
 
 front views A and B, and tlie construction of the 
 internal parts in the section c. The frame of the 
 machine is a heavy casting, a , of high and elongated 
 form, in the two ends of which are two deep horizontal 
 recesses, b b v In the right-hand one, as seen in c, is 
 bored a vertical hole, about half an inch larger than the 
 largest size of hole intended to be punched, and on the 
 planed surface at the upper end of this hole rests the cast 
 
 steel die o. This is pyramidal 
 in form, and has a vertical hole 
 through it, the top of which is 
 bored exactly circular to a dia- 
 meter slightly larger than that 
 of the punch n. The lower 
 portion of the hole in o is made 
 a little larger in order to allow 
 the round block of metal that 
 is punched out of the plate 
 operated upon to fall down 
 freely without frictional resis- 
 tance. The punch n is a short, 
 nearly cylindrical, piece of steel, 
 which is slipped into a tapered 
 socket in the slide m. The 
 punch corresponds in size with 
 the die, and for each punching 
 
 Fig. 54, b.— End view (Punching machine there must be a set of 
 end) of Punching and Shear- -i • ~i n r» n xi 
 
 ing Machine. dies and punches tor all the 
 
 sizes of holes desired to be 
 
 punched. The sizes in such a series usually increase 
 by sixteenths of an inch in English machines. The 
 bottom part of the punch is very slightly tapered 
 for a short distance, so that the lowest diameter is the 
 largest, and the higher portions of the tool can pass with- 
 out friction into the holes formed by the lower edge* 
 This upward narrowing is continued a small length only, 
 the upper part of the punch being tapered in the contrary 
 direction, in order to gain a larger, and consequently less 
 
Chap. IX.] 
 
 PUNCHING MACHINE. 
 
 213 
 
 severely stressed, section for the body of .the tool, and 
 also in order that the upper part of all the punches of 
 smaller size should fit the socket made in accordance 
 with the diameter of the largest of the series. The die 
 o is held in place by three horizontal set-screws, by means 
 of which it can be set with accuracy vertically underneath 
 
 the punch, which at the bottom of its stroke should enter 
 the die by about g\- of an inch. The plate to be punched 
 is laid horizontally resting on the die o, and its edge may 
 be pushed back as far as the back of the recess 6, or any 
 distance less than this at which it is desired to place the 
 hole. The punch is forced down by the slide m, and it fits 
 so tightly in the hole made in the plate that in rising 
 again its friction lifts the plate upwards. In order to 
 free the plate of the punch, it is kept from rising more 
 than a short distance by the pronged guard n fastened 
 immovably to the frame at n Y . This guard is placed at 
 such a height that it admits between it and the die the 
 thickest plate that it is intended ever to operate upon. 
 The casting m in which the punch is placed moves up 
 
214 
 
 CUTTING TOOLS. 
 
 [Chap. IX. 
 
 and down a dove-tail grooved slide, formed of a flat 
 vertical surface and strips screwed on as seen in the end 
 view. In m there is a broad rectangular slot cut, in which 
 works a square block fitting the slot vertically, but shorter 
 than it horizontally, so that it may have in the slot a to- 
 and-fro motion equal to the required vertical stroke of 
 the punch — i.e., two or three times the greatest thickness 
 of plate to be dealt with. In the square block is a 
 cylindrical hole into which enters an eccentric pin e L , 
 turned on the end of the shaft e. As this shaft turns 
 the eccentric pin actuates, through the block, the slide m 
 in its up and down motion. It will be observed that the 
 lower edge of the slot in m consists of a separate small 
 plate, to which is screwed the handle By this handle 
 the plate can be pulled forward into a recess made for it 
 in the front part of m — i.e., farther than the front end of 
 e 1 and of the square block. In this position it leaves the 
 slot in m of a square shape, and of such size that e l and 
 the square block may perform their circular motion with- 
 out driving m. By this means the handle \ serves to 
 throw the punching end of the machine “ out of gear.” 
 The slide then remains in its mean position, being held at 
 that level by the friction in the guide-grooves. In order 
 that its weight may not make it fall in spite of this fric- 
 tion, it is often linked to a horizontal lever lying over it 
 with a fulcrum on the frame and a counter-balance weight 
 at its inner end. A small hole may be seen in the sec- 
 tion c bored obliquely through the upper part of m. 
 This hole is continued down through the top half of the 
 square block. Its object is to lubricate through it the 
 sliding surfaces of the block and of the eccentric pin e Y 
 3. Shearing Machine. — The shearing machine is at 
 the other end of the shaft. It has a gap, b l9 of equal depth 
 in the present example to that of the punching end. The 
 shearing consists in cutting one portion of plate from the 
 other along a straight line, and this is done in exactly the 
 same way as that in which an ordinary pair of scissors acts. 
 The shearing blades are flat stout plates of steel, marked 
 
Chap. IX.] 
 
 SHEARING MACHINE. 
 
 215 
 
 6’ and t in the side view. These are fastened by counter- 
 sunk screws, the lower one to the frame of the machine 
 and the upper one to the slide r, which is similar and 
 similarly moved up and down by the shaft e to the slide 
 m that actuates the punch. There is an eccentric pin e 2 , 
 the square sliding block surrounding which can be thrown 
 out of gear by drawing out the handle q { . The shear 
 blades are placed so that the plane of the face of the one 
 coincides with that of the opposed face of the other. The 
 edges are straight, and are ground so as to give a cutting 
 angle of slightly less than 90°. The edge of the lower 
 blade is horizontal : that of the upper one is inclined to 
 the horizontal at a small angle, so that the shearing action 
 commences at one end and proceeds gradually towards 
 the other. 
 
 In the machine illustrated the shear blades are not 
 perpendicular to the length of the frame, that is, to the 
 shaft e. The object of this is to facilitate the cutting of 
 the ends of plates obliquely. The back of the gap b 1 is 
 placed obliquely at the same angle. Since the bearing 
 surface of the slot in the slide r, in which the eccentric 
 and block work, must be perpendicular to the shaft, the 
 slide r takes in cross section a nearly triangular shape. 
 The centre of the thrusting surface of the eccentric 
 block should be placed vertically over the middle of the 
 shear blade edges. The weight of this slide is often 
 counterbalanced in the same way as already described 
 for the punching end of the machine. 
 
 The commoner arrangement is to have the blades at 
 right angles to the shaft. In one very convenient ar- 
 rangement, illustrated in Fig. 56, the blades are fixed to 
 separate disc castings bolted on horizontal circular faces 
 on the frame and on the lower end of the slide respec- 
 tively. These can be shifted round and clamped in posi- 
 tion at any desired inclination to the shaft. 
 
 4. Driving Mechanism. — The shaft e is supported at 
 two bearings at its ends and at two others near its centre 
 in bosses cast in the frame. Between these bosses comes 
 
216 
 
 CUTTING TOOLS. 
 
 [Chap. IX. 
 
 a large spur-wheel. This is driven by the upper shaft d 
 by means of the pinion h. 
 
 The shaft d also is supported in bearings in the frame, 
 the boss on the right-hand side being extended close up 
 to the pinion A, because this is the driving end of the 
 shaft, i.e., the end through which the driving effort is 
 transmitted. The effort is transmitted from pinion to 
 wheel through the surfaces of the teeth in contact. The 
 force twists the two shafts, the twisting force or moment 
 being that which produces the desired rotation. The same 
 force, however, bends the shafts. This bending, although 
 unavoidable, is not desired and, in fact, is injurious. It 
 is, therefore, reduced to a minimum by placing the bear- 
 ing as close as possible to the mean point of application 
 of the force which is in the centre of the length of the 
 pinion. The design of the machine would be still better 
 than as in the drawing if the boss on the left-hand side 
 in c also came close up to the pinion. All shafts in 
 machinery should be prevented, as far as possible, from 
 bending by placing the bearings as near as they can be 
 arranged to the places of application of transverse force. 
 The bending results in waste of energy, in the form of 
 vibration and heating of the shaft, and it is still more 
 injurious in unduly wearing the edges of the journals, 
 and in thereby wasting a still further quantity of energy 
 in heating the journals. 
 
 At the end of the shaft there are two pulleys, f one 
 
 loose and the other fast, by a belt running over the latter 
 of which the machine is driven. When it is not desired 
 to run it, the belt is shifted by a fork overhead on to the 
 loose pulley. 
 
 On this upper shaft there are two fly-wheels g and g lt 
 These are necessary on account of the great variation in 
 the resistance. During the upward stroke of the tools no 
 work is done except in overcoming the friction at the 
 sliding surfaces, and in lifting the weights of the slides m 
 and r if these are not counterbalanced. It is only 
 during a fraction of the downward stroke that work is 
 
Cliap. IX.J STORAGE OF ENERGY IN FLY-WHEELS. 
 
 217 
 
 done, tlie size of the fraction depending on the thickness 
 of the plate that is being shorn or punched. During this 
 small time the effort required is greater than can be 
 exerted by the belt, through its frictional connection with 
 the pulley over which it runs. The deficiency is made up 
 during the rest of the revolution. Energy is delivered 
 by the belt to the pulley at a tolerably uniform rate 
 throughout the whole revolution of the shaft e. While 
 none of it is being spent in cutting, this energy has the 
 effect of slightly increasing the speed of the moving parts 
 ■ — i.e., additional kinetic energy, or energy of motion, is 
 stored up in them. The heavier these parts are the 
 greater is the quantity of additional kinetic energy cor- 
 responding to a given increase in velocity, and, there- 
 fore, in order that the whole energy delivered to the 
 machine during the non-cutting period of the stroke may 
 be stored up in this way without involving a large varia- 
 tion of speed, the heavy fly-wheels are added. During 
 the cutting, when the supply of energy by the belt is in- 
 sufficient to meet the demand, the fly-wheels give up once 
 more the kinetic energy stored in them, helping the belt 
 to drive the punch or shears through the plate. 
 
 As mentioned already, the stroke of the punch is 
 made much greater than the greatest thickness of plate 
 to be perforated. The object of making it so is partly to 
 allow a larger portion of the revolution for the storing 
 of energy in the above-explained manner, and partly — 
 perhaps chiefly — to allow an interval of time between the 
 successive entrances of the tool into the plate sufficient 
 to permit the workmen to shift the plate correctly into 
 the new positions for the next holes The forked guard 
 over the plate enables them to do this with considerable 
 exactitude when the holes are previously marked out with 
 chalk, and with practice it can be done very rapidly. 
 
 5. Whitworth’s Driving Gear. — Many variations 
 are adopted by different makers in the modes of making 
 the driving connection, between the eccentric pins on 
 the shaft e and the slides. The design used by Sir 
 
218 
 
 CUTTING TOOLS. 
 
 ("Chap. IX. 
 
 Joseph Whitworth is a good one. Fig. 55 shows 
 this. The shaft (in end view) is marked e, and the 
 eccentric pin e 1 . The block in which e 1 is inserted 
 takes a triangular form k , shown clearly by the shaded 
 edge. The slide l has cut in it a triangular slot, corres- 
 ponding in general shape to k , of the same depth but 
 
 wider by an extra breadth 
 equal to the throw - of the 
 eccentric so that k may rock 
 to and fro in it at its top 
 end. The rounded lower cor- 
 ners, o , of the two triangles 
 are curved to the same radius, 
 and the one rocks inside the 
 other through a very small 
 arc only. The upper edges, 
 p p y>, are curved to the same 
 centre as these lower corners, 
 so that the block k always fills 
 the slot vertically, whether it 
 be upright, as in the figure, 
 or thrown to one side. The 
 chief advantage of this design is that while on the up- 
 ward stroke, when little pressure is being exerted between 
 the block and the slide, this small pressure is exerted at 
 the surfaces p p p, where the maximum sliding motion 
 occurs between the two, and on the downward stroke, 
 when intense force is being transmitted, the pressure is 
 at o y where only very small sliding motion occurs. Loss 
 of energy by friction is thus avoided. 
 
 6. Hydraulic Punching and Shearing Machine. — 
 In the machine thus driven by a belt and an eccen- 
 tric pin there are two faults. One has already been 
 explained — it is the necessity of storing up energy to 
 develop an extra great rate of working for a minute 
 period , the other is that there can be no variation of 
 the length of stroke to suit different thicknesses of plate. 
 These defects do not exist in the Hydraulic Punching 
 
 i 
 
 \ 
 
 I 
 
Fig. 56 . — Tweddeli/ s Hyde, atjlic Punching and Shearing Machine. 
 
220 CUTTING TOOLS. {T^ap. IX. 
 
 and Shearing Machine, shown in Fig. 56, which is designed 
 and made by Mr. Tweddell. Here an hydraulic cylinder 
 stands directly over each of the two tools for shearing 
 and punching. The plungers of these cylinders take the 
 places of the slides in the before described machine, the 
 tools being directly inserted in their lower ends. The 
 full power required for penetration of the material is 
 obtained by the water pressure acting on the large sur- 
 faces of these plungers, and this force acts through a 
 distance only equal to the stroke of the tool. This stroke 
 also is variable for different thicknesses. As already 
 stated, the shears may be clamped at any angle to the 
 centre line of the frame. The water is admitted for 
 each stroke through a valve actuated by a hand-lever, 
 and at the end of the stroke an escape- valve opens 
 automatically, and the plunger, being counterbalanced with 
 an excess of weight, is drawn upwards to be ready for a 
 new stroke. The supply- valve being opened by hand, the 
 interval between each stroke may be made whatever is 
 necessary for the setting of the work correctly in position. 
 
 Small portable punching machines could easily be 
 made on this principle, to be slung by chains into 
 position for any odd work on large structures, such as 
 bridges and ship work. 
 
 7. Multiple Punching Machine. — The principle of 
 multiple punching does not yet seem to have been intro- 
 duced into practice. This might be done with great 
 advantage. A series of sockets might be placed in the 
 lower edge of the slide to hold as many punches with a 
 corresponding row of dies underneath them, both series 
 being adjustable to any pitch desired. Beyond the for- 
 ward end of the row of dies there would be fixed a gauge- 
 peg, simultaneously adjustable with the dies to the same 
 pitch from the last of the dies. When one set of holes 
 had been punched by one stroke of the machine, the last 
 hole so punched would be slipped over the gauge-peg, and 
 this would ensure the succeeding stroke making the next 
 set of holes at the right distance from the former set. 
 
Chap. IX. 
 
 SHEARING ACTION. 
 
 221 
 
 8. Mode of Rupture by Simple Shear. — The action 
 of the shearing blades upon the plate is very simple. 
 This is in consequence of the cutting angle being less 
 than 90°, whereby it is ensured that the surface of the 
 plate rests wholly on the edges of the top and bottom tools. 
 The cutting edges sink slightly into the plate, the surfaces 
 of which are compressed over a strip of very narrow 
 breadth. The force is exerted through a slice of material 
 of this breadth, of depth equal to the thickness of the 
 plate, and of length equal to that of the portion of the blade 
 that is in action at any instant. This portion of material is 
 subjected to intense shearing stress — that is, the portion of 
 it at one side is forced to slide over that at the other. Such 
 sliding is called “ shearing strain.” It may take place to 
 a considerable extent without actual rupture occurring, 
 as when a piece of material is twisted. In the present 
 case it is carried so far that the two opposite surfaces 
 part company, and the plate is separated in two pieces. 
 The cut is a comparatively clean one, because the shearing 
 stress has been so localised within such narrow limits. 
 Outside the minute breadth mentioned above, the 
 material remains almost wholly unstressed, and, there- 
 fore, there is no chance of the surface of rupture wander- 
 ing more than the smallest perceptible distance from the 
 plane connecting the edges of the top and bottom blades. 
 The broken surface is slightly ragged, but is quite flat. 
 
 It is to be observed that the whole force of the 
 rupturing action is exerted through as small a section 
 of the blade-material as of the plate, and as this latter is 
 broken it is only owing to the superior strength of the 
 steel of the blade that the operation is at all possible. 
 
 9. Mode of Rupture in Punching. — The shearing out 
 of a cylindrical portion by the punch would be exactly 
 similar to that described above, giving an even breakage 
 if the cutting edges of the top and bottom tools were made 
 with cutting angles somewhat le^s than 90°. In order 
 that they should be so, the upper surface of the die would 
 need to be coned, and the under surface of the punch 
 
222 
 
 CUTTING TOOLS. 
 
 [Chap. IX. 
 
 hollowed to a cup-shape, as in Fig. 57. The edges so 
 sharpened, however, would be difficult to maintain, there 
 being no easy means of re-grinding them when blunted. 
 The top of the die is made flat instead, and some makers 
 make the face of the punch slightly convex instead of 
 
 concave. The result is that severe 
 | I pressure is distributed through an 
 
 1 annular portion of the plate the 
 
 | p inside diameter of which is much 
 
 smaller than that of the tool, 
 
 while its outside diameter extends 
 considerably beyond the circum- 
 ference of the hole in the die. The 
 
 rig. 57. first effect of the application of 
 
 the punch is the crushing of the 
 top of the plate within the circle of the hole about to be 
 formed and to a small depth beneath the surface. In 
 sinking, this portion of the material drags downwards 
 with it the surrounding portion outside the circle. This 
 cannot be dragged downwards far, because the plate is 
 supported underneath, and, in fact, it can sink only in so 
 far as it also becomes compressed. It, therefore, resists 
 the downward force by sheer stress over the vertical cylin- 
 drical surface, and the material becomes violently twisted 
 throughout a certain radial distance. It is to be observed 
 that these actions do not extend through the whole thick- 
 ness of the plate (unless this is very thin), but at the 
 beginning reach only to a certain depth from the surface. 
 The downward compressing force inside the circle 
 gradually expends itself in producing shearing forces 
 that are transmitted laterally to the outside of the circle. 
 When a certain depth has been reached, at which the 
 sum of the laterally transmitted shearing forces equals 
 the total downward thrust of the tool, the vertical com- 
 pressive stress is reduced to zero. Above it the strain 
 increases until the shear over the lateral walls of the 
 
 crushed portion becomes so great that rupture takes 
 place. The rupture occurs along the lines where the 
 
Chap. IX.] 
 
 MODE OF RUPTURE IN PUNCHING. 
 
 223 
 
 stress lias been greatest, and these are nearly but not 
 quite vertical. The broken surface is thus conical, the 
 apex of the cone being above. The angle of this cone 
 depends conjointly on the character of the material, on 
 the difference between the die-hole diameter and the 
 punch diameter, on the plate thickness. 
 
 After this rupture, these vertical surfaces, which were 
 previously clinging together, cease wholly to transmit 
 force laterally. The whole of the thrust applied at the 
 upper surface by the punch is now transmitted down to 
 the bottom of the breakage, and the part above this point 
 proceeds to act on the part below it in the same way that 
 the punch-tool itself acted upon the upper portion, the 
 action differing in that the lower face of this plug has 
 no defined cutting edge, and that the thrust is more 
 evenly distributed over this face than it was originally 
 over the face of the punch. The whole process above 
 described now re-commences ; a similar set of forces is 
 developed at a lower level under only slightly altered 
 conditions, and then on a new short conical surface the 
 shear-strain increases until rupture again takes place. 
 If this second rupture does not carry the breakage wholly 
 through the plate, the process is repeated a third time, and 
 occasionally a fourth time. The successive ruptures do 
 not take place along the same conical surface, each broken 
 surface lying inside the mathematical extension of the one 
 above it. The short conical shorn surfaces are connected 
 by small, very ragged circular shelf-surfaces, which are 
 called “ burrs,” and which are a great inconvenience in 
 the subsequent process of riveting the plates together. 
 
 The action of the cutting edge of the die on the 
 under surface is quite similar to that explained above as 
 taking place at the upper surface. 
 
 10. Error in the Ordinary Calculation of the 
 Strength of Punches. — It will thus be seen that, except 
 in the case of thin plates, where no burrs are discovered 
 inside the punched holes, the operation of cutting 
 through the plates is not an instantaneous one, nor 
 
224 
 
 CUTTING TOOLS. 
 
 [Chap. XX. 
 
 one in which all the different parts of the surface 
 are cut simultaneously. The whole is done bit by 
 bit, and the stress on the tool is correspondingly re- 
 lieved. . The strength of the tool to do its work has 
 been usually calculated as if it had to exert a thrust 
 sufficient to overcome the resistance to shear-rupture 
 of a surface equal to the circumference of the hole 
 multiplied by the whole thickness of the plate. By this 
 theory a certain thickness is calculated, beyond which 
 the punch must have insufficient strength to pierce the 
 plate. The above explanation shows, however, that such 
 a calculation must be wholly erroneous, and would give a 
 much smaller limiting thickness than the true one. The 
 resulting error is partly counterbalanced by the addi- 
 tional error made in assuming that the thrust of the punch 
 is uniformly distributed over its horizontal section. It is 
 actually to a great extent concentrated at its edges, and 
 this concentration evidently greatly diminishes its effec- 
 tive strength and the depth of material which it can pierce 
 without itself breaking. It- is probably to avoid this con- 
 centration of the stress at the edge that Sir J oseph Whit- 
 worth and other makers have made the under surface of 
 the punch slightly convex. 
 
 11. Relation between Shearing and Punching* and 
 other Cutting Machines. — The action of shearing and 
 punching is a true cutting action, although it is of a 
 rough character, and the above explanation will greatly 
 assist in the right comprehension of the mode of cutting 
 in planing machines and turning lathes. The greatest- 
 difference between the two really lies in the effect of the 
 keener cutting edge of the latter, and the smaller thick- 
 ness of the layer of material removed by them, whereby 
 the cutting stresses and strains are more effectually 
 localised. The remaining difference between the cases 
 consists in the altered ratio in which shearing, tensive, 
 and compressive forces are active, in producing the sepa- 
 ration of the part which has to be removed. 
 
225 
 
 CHAPTER X. 
 
 TOOL STEEL. 
 
 1. General Characteristics of Steel. — Steel used to 
 be well defined by saying that it was any compound 
 of iron and carbon which could be forged, and which 
 would also harden when plunged hot into water or 
 other cooling liquid. The manufacture of steel has 
 so much changed and improved that this could hardly 
 be taken at the present time as an accurate defi- 
 nition. What is called “ very mild steel,” or used 
 to be called by the remarkably non-descriptive term of 
 u homogeneous metal,” contains a very small percentage 
 of carbon, sometimes not more than one- or two-tenths 
 per cent., and the hardening effect upon this material of 
 sudden cooling is so slight as to be hardly perceptible. 
 With so small an admixture of carbon, the material is 
 very ductile. With y^th per cent, carbon a bar of 
 Bessemer steel will stretch about 16 per cent, of its 
 length before breaking. As the percentage of carbon is 
 increased, the ductility decreases rapidly, but the tensile 
 strength and the hardness obtained by sudden cooling are 
 increased. The greatest tensile strength is obtained in 
 Bessemer steel, with about lj per cent, carbon, and with 
 a somewhat higher percentage in crucible steel. Bessemer 
 steel is in ail circumstances unfit for tool-making, on 
 account of certain impurities which are not got rid of in 
 this process of steel manufacture. If the carbon is more 
 than 2 per cent., it is impossible to forge the material, 
 because it cracks and crumbles when red-hot under even 
 light blows from the hammer. With a considerably 
 less proportion of carbon than this the forging is still 
 difficult, and indeed the forging becomes always more 
 difficult the larger the amount of carbon contained. Thus 
 p 
 
226 
 
 CUTTING TOOLS. 
 
 [Chap. X. 
 
 even mild steel is apt to split and show brittleness if 
 worked at a welding heat. The temperature under which 
 the different qualities of steel must be worked at the 
 forge must thus be less the more carbon contained in it. 
 This is the most important rule that requires to be 
 followed in the manipulation of steel, and it is of very 
 special importance in the treatment of tool steel. This 
 requires a high percentage of carbon in order to obtain 
 the desired hardening and tempering qualities, and is 
 completely ruined if it be exposed at the forge to a higher 
 temperature than a certain limit, which is different for 
 different qualities, but which always lies much below the 
 welding or white heat. 
 
 2. Manufacture of Tool Steel. — The steel suitable 
 for tool-making is prepared from “ blister steel,” which 
 in its turn is produced from wrought-iron bars by the 
 process called “ cementation,” this process consisting in 
 the absorption of carbon into the iron bars at a high tem- 
 perature. The “ blister steel ” is converted into “ shear 
 steel ” by faggoting, re-heating, hammering, and rolling. 
 This shear steel is used for ' some classes of tools, such as 
 pickaxes and spade-edges, that do not require keen edges, 
 and are exposed to violent shocks. But the majority of 
 tools are made from “ cast ” or “ crucible ” steel. This 
 is produced by melting fragments of blister steel in 
 crucibles, and casting the molten metal into moulds, so 
 as to form “ ingots,” which are then hammered, rolled, 
 and forged into the various required forms. Experiments 
 made at Crewe in manufacturing tool -steels by the 
 Siemens-Martin process have had a fair measure of 
 success. 
 
 3. Combined Carbon. — The melting has the effect 
 of giving much greater uniformity of character and 
 quality throughout the mass of the product. With- 
 out such uniformity the steel is quite unfit for tool- 
 making. Crucible steels containing from | to 1-J per 
 cent, of carbon are suitable for different kinds of 
 tools, about 1 per cent., perhaps, being the average 
 
Chap. X.j 
 
 TOOL STEELS. 
 
 227 
 
 for tools for machining, such as turning and planing, 
 and as much as 1^ per cent, the average for “ edge 
 tools.” As already mentioned, such steel can be made 
 very hard by heating it to a red heat, and plunging it 
 suddenly in a cooling liquid. Before such hardening a 
 part of the carbon exists intimately mixed, but not 
 chemically combined, with the iron ; but the larger 
 portion of it is combined as a carbide of iron. The 
 heating effects the combination of the previously uncom- 
 bined carbon, and the sudden cooling fixes this combina- 
 tion ; so that in the hardened steel the whole of the 
 carbon is found to be in the form of carbide. On the 
 other hand, very slow and gradual cooling favours the 
 separation once more of a certain portion, which assumes 
 again the form of uncombined graphite. The resulting 
 product is soft, and the gradual cooling is called “ anneal- 
 ing.” It has never been definitely settled whether the 
 hardness or softness is chiefly due to the greater or less 
 amount of chemical combination between the iron and 
 carbon. All that can be said is that the state of hard- 
 ness is accompanied by the more complete combination. 
 
 4. Silicon. — Besides carbon, silicon is another con- 
 stituent which exercises a very distinct influence on the 
 character of the metal according to its quantity. Its 
 influence is in the same direction as, and very similar to, 
 that of carbon. In fact, to a large extent silicon seems 
 to be able to take the place of carbon, except that even a 
 smaller quantity of silicon than of carbon makes the 
 metal unforgeable ; while, on the other hand, to produce 
 the same degree of hardening quality a larger proportion 
 of silicon than of carbon is required. A small quantity 
 of silicon is desirable in cast steel, because it prevents the 
 formation of “ air-holes,” but a larger proportion than is 
 needed to effect this object should be avoided. 
 
 5. Other Constituents. — Many tool steels contain a 
 certain quantity of manganese, and the presence of this 
 constituent makes forging and welding more easy. It also 
 neutralises to some extent the evil (red-shortness) created 
 
228 
 
 CUTTING TOOLS. 
 
 [Chap. X. 
 
 by the admixture of sulphur, which it is difficult to get 
 rid of perfectly. Phosphorus is another impurity, which 
 is even more destructive of good quality than is sulphur. 
 Tungsten and titanium are said to have a decided in- 
 fluence in improving the toughness of the steel. Small 
 quantities of copper, silver, and arsenic, are also said to 
 improve its quality. Lastly, nitrogen is an invariable 
 ingredient in steel, and it is now" generally admitted that 
 the admixture of both carbon and nitrogen are necessary 
 for the production of steel ; the presence of neither of 
 these two separately is sufficient. It must not be con- 
 cluded that the quality of steel is necessarily high because 
 it contains a relatively large proportion of nitrogen, 
 although apparently under this idea some tool steels are 
 advertised as being “ nitrogenous.” The modification of 
 quality due to separate increase of the proportion of 
 nitrogen has not yet been determined by experiment, and 
 conjecture in such a matter is likely to be delusive. 
 
 6. Special Brands. — Many special steels have gained 
 a wide reputation for toughness combined with hardness. 
 Among these may be mentioned Mushet’s steels, in which 
 titanium, tungsten, and wolfram, are said to be important 
 constituents. Among long-established English brands of 
 tool steel is Huntsman’s, but its good quality appears to 
 be due more to careful mechanical treatment than to 
 special chemical constitution. Edgar Allen & Co., of 
 Sheffield, furnish two extremely fine-grained, hard, and 
 enduring steels, called “ adamantine ” and “ self-har- 
 dening.” These high-class steels all require to be forged 
 at the very low T est possible heat. Allen’s “ self-hardening ” 
 steel contains '95 per cent, carbon, '33 per cent, 
 manganese, and *21 per cent, silicon. Both Mushet’s 
 “ self-hardening ” (made by Osborne & Co., of Sheffield) 
 and Allen’s “ self-hardening ” require no water-cooling, 
 but are hardened by being left to cool in the air from a 
 low red heat. 
 
 7. Hardening and Tempering. — When a piece of 
 steel has been hardened by heating to a red heat and 
 
Cliap. X.J STEEL AT DIFFERENT TEMPERATURES. 
 
 229 
 
 sudden cooling, it can be partially softened again by re- 
 heating to a low temperature and cooling suddenly once 
 more. There is some confusion of practice in naming 
 these two processes. By many, and especially by book- 
 writers, the word “ tempering ” is used to mean the 
 complete double process of hardening and subsequent 
 partial softening. Others refer to the latter alone — i.e ., 
 the partial softening- — by the term tempering. It is 
 much to be desired that this latter use of the word should 
 be adhered to, as great inconvenience and frequent mis- 
 apprehension arise from the use of one term for two 
 distinct and wholly different — in fact, quite opposite — 
 operations. 
 
 8. Colour Scale of Temperatures. — As steel is 
 heated to higher and higher temperatures, its surface, 
 if perfectly clean, assumes successively the following 
 colours : — 
 
 Pale straw yellow at about 430° Fahr. This yellow colour 
 gradually deepens in shade until there is reached 
 
 Brownish-yellow at about *500° Fahr., Avhich darkens to 
 
 Light purple at about 530° Fahr., which gradually deepens 
 and shades into 
 
 Dark blue at about 570° Fahr. This blue becomes lighter, 
 and eventually becomes pale blue, tinged with gieen, at 
 about 630° Fahr. 
 
 Urging the temperature still higher, the metal becomes 
 successively — 
 
 Black, dark cherry red, glowing red, bright red, orange, 
 bright yellow, white, and scintillating white, 
 
 at which last temperature the steel very rapidly burns 
 away in the air, and above which temperature it becomes 
 decidedly pasty as it approaches the melting-point. 
 
 9. Various Effects of Sudden Cooling. — If a piece 
 of unhardened steel be heated through the yellows 
 and blues up to the black temperature, but not so 
 far as to show any red colour, and then be suddenly 
 quenched in some cooling liquid, it will be found to have 
 
230 
 
 CUTTING TOOLS. 
 
 [Chap. X. 
 
 been hardly altered in texture as exhibited on a fractured 
 surface, or in hardness as tested by the file or the grind- 
 stone. If, however, it be heated to the dark cherry red, 
 it will be found to be both greatly hardened and made 
 finer-grained in texture on the broken section, and also 
 strengthened against a tensive fracturing stress. All 
 these three effects will be increased if the temperature 
 before quenching be raised to glowing red. By quenching 
 at successively higher temperatures than this, the grain 
 is once more made coarser and more open, so that the 
 quenching from a bright red gives much the same fine- 
 ness of texture as that of the original unhardened bar, 
 while quenching from a white heat leaves it much coarser 
 than this. The strengthening effect also is continuously 
 decreased by quenching from higher temperatures up to 
 bright yellow, and quenching from the white heat pro- 
 duces great brittleness. The hardening effect, on the 
 contrary, is continuously increased by quenching from 
 higher temperatures right up to the dazzling white heat. 
 
 The amount of tensile strengthening derived from 
 this hardening process depends greatly upon the cooling 
 liquid, and also upon the per-centage of carbon in the 
 steel. Cooling in oil strengthens very much more than 
 cooling in water ; and cooling in warm water or salt 
 water, or water with some salt and flour mixed with it, 
 gives greater toughness than plain water-cooling, espe- 
 cially in the case of highly-carburised, that is, tool steels. 
 The strengthening effect, however, is much more strongly 
 marked in mild than in tool steels. 
 
 10. Different Cooling Substances. — It has already 
 been stated that this hardening process effects the 
 complete combination of all the carbon with the iron 
 as a carbide. The amount of hardening does not only 
 depend upon the temperature from which the cooling 
 takes place — i.e., upon the range of cooling — but also 
 very greatly upon the rapidity of cooling, the more 
 rapid cooling effecting the greater hardening. Different 
 substances cool more or less quickly, according to their 
 
Chap. X.] 
 
 LIQUID COOLING-SUBSTANCES. 
 
 231 
 
 power of conducting heat, and also in proportion to theii 
 specific heat — i.e., the amount of heat needed to raise 
 unit weight through 1° temperature. The rate of cooling 
 is also proportional to the difference of temperature 
 between the steel and the cooling substance. Metals 
 have, therefore, other things being equal, and with the 
 same differences of temperature, much greater cooling 
 power than other substances. Thus a thin piece of steel 
 can be intensely hardened by heating it and laying it 
 between two clean and thick pieces of metal, such as 
 iron or, still better, copjoer. The difficulty in using solid 
 pieces of metal for the purpose lies in the impossibility of 
 getting them to touch all over the surface of the steel to 
 be cooled. Even if the cooling metal were made in the 
 form of a thick box inside, which exactly fitted the hot 
 piece of steel, immediately after dropping this latter into 
 such a box it begins to contract through cooling, while 
 the box expands through heating, so that the “fit” is 
 immediately destroyed. Now, the cooling takes place 
 mainly through the surfaces lying in contact with each 
 other. For this reason it is necessary to use liquid 
 cooling substances. Mercury is the only metal which is 
 liquid at ordinary temperatures, but the expense of a 
 bath of mercury, and the deleterious fumes arising from 
 it when any portion of it is heated, prevent its being 
 used. Other molten metals, such as tin, lead, and zinc, 
 have been proved experimentally to be efficacious ; but 
 the high temperature, especially of the latter, enfeebles 
 their hardening action. This experiment, however, is 
 very important, because it proves that the hardening 
 effect is due wholly to sudden cooling down to about 
 500° or 600°, or perhaps only to 700° Fahr. Sudden 
 cooling below this limit (the exact limit has not yet been 
 accurately determined) has little or no further hardening 
 effect, and slow cooling from the same limit has little or 
 no softening effect. 
 
 Great hardness can be given small pieces by plunging 
 them into sealing-wax, the hot steel melting its way into 
 
232 
 
 CUTTING TOOLS. 
 
 [Chap. X. 
 
 the solid wax, and the piece being withdrawn and plunged 
 into new portions of the wax several times. 
 
 11. Water-Cooling by Evaporation. — Water is a 
 very bad conductor of heat, and the quenching of 
 steel in water is not effected by the conduction of 
 the heat away into the body of the water. The 
 heat only finds its way into the layer of water im- 
 mediately in contact with the hot steel, and this layer 
 is immediately evaporated into steam. Provided the 
 steam finds easy escape, fresh layers of water get 
 evaporated rapidly in succession, and since the steam 
 absorbs a great quantity of heat in being generated, the 
 steel becomes very rapidly cooled. It is, however, 
 necessary to allow the steam to escape freely from every 
 part of the surface to be hardened. This is effected by 
 moving the piece through the water and turning it round 
 to and fro. The best possible method of securing a 
 continuous fresh supply of water to the surface is to let 
 a jet in the form of fine spray play upon it. A double 
 or triple jet must be used in order to get different sides 
 acted on equally and simultaneously. 
 
 12. Lead Bath. — A red-hot lead bath is sometimes 
 used for heating, prior to hardening, pieces so large 
 that they are apt to crack in hardening from unequal 
 cooling. It has the disadvantage^ that the lead sticks 
 in sharp comers, such as those between the teeth 
 of milling cutters and the grooves of rimers. The 
 lead so sticking interferes with these parts receiving the 
 heat and cooling properly in the subsequent tempering, 
 and therefore such parts are covered with a carbonaceous 
 paste before the piece is plunged in the lead bath, which 
 jDrevents the adherence of such fragments of lead. 
 
 13. Tempering.: — The subsequent tempering consists 
 in removing some of the hardness produced by the 
 quenching, by means of re-heating to a low temperature. 
 The amount of softening is greater the higher the tem- 
 perature to which the steel is re-heated. Usually the 
 piece is again quenched when the proper low temperature 
 
Chap. X.] 
 
 TEMPERING COLOURS. 
 
 233 
 
 lias been reached. The resulting degree of hardness, of 
 course, depends on the quality of the steel, especially 
 upon the carbon per-centage, as well as on the tempering 
 heat. The following table of tempering colours is supplied 
 by Jonas and Colver, of Sheffield, for the high-class steel 
 they supply. The different tools are arranged in the 
 list in the order of the successively higher temperatures 
 to which they should be brought for tempering. 
 
 Faint straw . . 
 
 Brownish-yellow . 
 
 Light purj)le . . 
 
 Dark blue . . 
 
 . Scrapers for brass. 
 
 Steel engraving tools. 
 
 Light turning tools. 
 
 Hammer faces. 
 
 Planing tools for steel. 
 Planing tools for iron. 
 
 Paper- cutting knives. 
 
 Wood- engraving tools. 
 
 Flat drills. 
 
 Milling cutters. 
 
 Wire-drawing plates. 
 
 Boring cutters. 
 
 . Screw-cutting dies. 
 Leather-cutting dies. 
 
 Taps. 
 
 Chasers. 
 
 Bock drills. 
 
 Punches and dies. 
 
 Bimers. 
 
 Shear blades for metal. 
 Gauges. 
 
 Stone -cutting tools. 
 
 Plane irons. 
 
 Twist drills.. 
 
 Wood borers. 
 
 . Cold chisels for steel. 
 
 Axes and adzes. 
 
 Cold chisels for cast-iron. 
 Firmer or mortising chisels. 
 Cold chisels for wrought-iron. 
 Circular saws for metal. 
 
 . Screwdrivers. 
 
 Springs. 
 
 The same firm manufacture steel of different degrees 
 of carburisation, which they number from 1 up to 6. Of 
 
234 
 
 CUTTING TOOLS. 
 
 [Chap. X. 
 
 these No. 2 is suitable for turning, planing, and drilling 
 tools ; Nos. 3 and 4 for rimers, taps, milling cutters, and 
 chisels ; and Nos. 5 and 6 for punches, shear blades, 
 screwing dies, and hammers. 
 
 Thomas Chatwin, of Birmingham, tempers shear 
 blades and engineers’ taps to light straw ; gasfitters’ taps 
 and screw-dies to a straw a shade darker, and chasing 
 tools to a dark straw ; twist drills and chipping chisels 
 to a bluish-brown, i.e., practically the same as in tho 
 above list ; the small circular knives of tube- cutters to a 
 purplish-blue \ cylindric gauges to a very faint straw, 
 to ensure the best wearing quality. 
 
 14 .. — Cracking and Warping. — In hardening there is 
 much risk of splitting, owing to the cooling and contrac- 
 tion of different parts at different rates, and this also not 
 unfrequently produces distortion. The risk of these 
 mishaps, however, is generally still greater in the tem- 
 pering, because in the hardening we have at least a 
 uniform temperature throughout the mass to start with, 
 whereas it is very difficult to arrive at an equal tempera- 
 ture throughout in the low heating necessary for temper- 
 ing. Many different methods are therefore adopted to 
 heat the objects for tempering. Large massive pieces are 
 usually heated over a coke fire in a close oven, and some- 
 times in a muffle heated either by coal fire or by gas, the 
 most perfect method being that of dipping in a hot bath of 
 oil or molten metal, the particular alloy chosen for the 
 bath being suited to the temperature desired. Small 
 pieces are most frequently heated simply on a hot plate 
 lying over a fire. The focus of the fire being at one end 
 of the plate, a gradually-rising temperature is reached by 
 pushing the objects slowly from one end to the other of 
 the plate. Such a plate, covered with a thick uniform 
 layer of sand, gives greater possibility of obtaining an 
 equal temperature throughout pieces of unequal thick- 
 ness, but is somewhat less handy for the workman to 
 deal with if he has to watch many pieces at the same 
 time. A small piece that presents peculiar difficulties in 
 
Cliap. X.] 
 
 EQUAL AND UNEQUAL COOLING. 
 
 235 
 
 getting the temperature uniform may be heated inside a 
 red-hot iron tube or ferrule.. Ordinary workshop tools, 
 such as chipping chisels and turning tools, are usually 
 re-heated by leaving unquenched in the hardening a 
 portion of the bar not desired to be hard, and then 
 allowing the quenched portion to be re-heated by con- 
 duction from this part that remains hot. In order to 
 stop the re-heating at the right temperature, the colour 
 is watched, and to make this visible it is necessary to 
 clean the surface perfectly. This can be done by rubbing 
 with a piece of sand or pumice-stone, and where many 
 articles are rapidly passing through the hands of the 
 temperer, a boy is kept to clean up the surfaces by 
 means of a rapidly-rotating buffing- wheel, fed with water 
 and sand or emery-powder. 
 
 When the quality of the material dealt with is not 
 very certain and is subject to even slight want of homo- 
 geneity, it is well to submit it to thorough annealing by 
 slow cooling before hardening and tempering, and the 
 desired result will be attained more certainly if the 
 annealing process be repeated more than once. Again, 
 inequality in hardness and texture due to unequal cooling 
 in hardening, may be rectified to a great extent by 
 repeating the tempering process twice, thrice, or even 
 four times. In doing so the re-heating for tempering 
 should be performed as slowly as possible, and oil, or 
 water covered with a layer of oil, should be used as the 
 dipping fluid. The cooling may also be allowed to take 
 place in the air, without the use of any liquid. 
 
 The shape of the article to be hardened has, of course, 
 a great deal to do with unequal or equal cooling of its 
 different parts; and this is influenced largely also by 
 certain parts necessarily entering the cooling fluid first, 
 while, on the other hand, the interior parts never come 
 in contact with this fluid. Those parts most freely 
 exposed to the cooling action are most rapidly cooled 
 while the internal portions cool only gradually, because 
 they do so only by having their heat transferred through 
 
236 
 
 CUTTING TOOLS. 
 
 [Chap. X. 
 
 the surrounding layers and external surfaces. Pieces 
 which are thin in some parts and thick in others, become 
 unequally hardened and are apt to crack. Tools with 
 hollow bosses may have the cooling of these central parts 
 accelerated by directing a small jet of water through the 
 hole in the boss. Such bosses, however, are very 
 frequently desired to be softer than the edges. The 
 cooling of the exterior may, on the other hand, be 
 retarded by various devices, such as clamping upon them 
 pieces of iron shaped to fit closely, or smearing them over 
 with a coating of loam bound on with wire. A coating 
 of prussiate of potash similarly bound on is also recom- 
 mended, the prussiate of potash having an extra hardening 
 effect by further carbonising the surface layer. This 
 latter process appears to be of particular value in pre- 
 venting cracks at sharp re-entrant corner angles. A 
 stout wire is wrapped into the corner, and the prussiate 
 is plastered over it. A coating of prussiate of potash is 
 also sometimes used to protect the surface from oxidation 
 in heating for hardening over an open fire. Such oxida- 
 tion is, of course, to be specially guarded against when 
 the piece to be operated on has been tooled over and 
 nicely finished. Here the exclusion of air from contact 
 with the steel surface is the object to be aimed at, and 
 this can be attained by placing the objects to be hardened 
 in a box, packing this up with wood or other charcoal 
 dust, and luting down the cover before inserting the box 
 in the fire. The surface layers will be further carburised 
 or “ steeled ” by this process. 
 
 Pieces that are found to cool or heat unequally, and, 
 therefore, crack in spite of any of the above precautions, 
 can frequently be dealt with successfully by somewhat 
 modifying the shape in such a way as not to interfere 
 with the necessary strength, and yet to reduce the mass 
 of metal at those parts which cool less rapidly than the 
 others. 
 
 It is evident that uniform heating is as important in 
 order to avoid cracking as is uniform cooling, and the 
 
ChajD. X.] 
 
 UNIFORM HEATING 
 
 237 
 
 same causes as regards shape, &c., make it difficult to 
 attain uniformity in the heating process. The difficulty 
 in heating, however, can be to a great extent overcome 
 by slow-heating. If the rate of heating were indefinitely 
 small, every part of the metal would certainly come to 
 almost exactly the same temperature. Hence arises the 
 value of the process termed “soaking,” which simply 
 refers to the finishing of the heating process very slowly. 
 The use of gas stoves in this trade has not yet, in the 
 opinion of the author, been sufficiently developed. By 
 them a closed chamber can be obtained with very uniform 
 temperature at every point of each level surface, a 
 graduation of heat being obtained from top to bottom of 
 the stove, and furthermore the flame can be made wholly 
 non-oxidising (or even carburising if desired) by suitable 
 regulation of the relative supplies of gas and air. 
 
 In forging before hardening, the hammering on the 
 anvil should be continued until the metal is quite cool. 
 If the tool has to be subsequently re-hardened, it should 
 be first heated to a low red heat, hammered until cool, 
 and then again heated for hardening. The hammering 
 gives fineness of texture and toughness. 
 
 In heating for tempering in oil, or with the article 
 smeared over with oil or tallow, George Ede says that the 
 first appearance of smoke rising from the oil indicates 
 the attainment of the temperature of 450° Eahr. When 
 the smoke rises copiously, the temperature of 500° Fahr. 
 has been reached, corresponding to the “ brown ” colour ; 
 still more abundant black smoke indicates 530° Fahr., or 
 the “purple” temper; and 580° Fahr., or “blue” temper, 
 is reached when the oil takes fire when a lighted match 
 is brought in contact with it. 
 
INDEX. 
 
 \ OCELERATION of momentum 
 in planing machines, 91 
 Adze, 12 
 Axes, 9 
 
 T> AND saws, 46 
 -*-* Boring bars, 184 
 
 — collar for lathes, 171 
 
 — large cylinders, 185 
 
 — machines, 181 
 Bow drill, 210 
 Braces for drilling, 207 
 Break lathes, 146 
 
 c 1APSTAN tool-rest, 170 
 ^ Chasing tools, 172 
 Chipping chisel, guidance of, 23 
 
 — chisels, 21 
 
 — hammer, 22 
 
 Chisel edge, penetration of, 24 
 
 — tools, relations between, 1 
 Chucking lathe work, 134 
 Ciicular saws, 46 
 
 cutting speed and fee 1, 54 
 
 — shaping, 98 
 
 Classification, principles of, 1 
 Cold chisel, 21 
 
 — iron saws, 58 
 
 Colour scale of temperatures, 229 
 Combined carbon in steel, 226 
 Cooling substances for hardening 
 steel, 230 
 
 Cracking and warping in cooling 
 tool steel, 234 
 
 Cutting action in planing metal, 71 
 of wood chisels and planes, 16 
 
 — angles of lathe tools, 154 
 of planing tools, 82 
 
 — pressure on lathe tools, experi- 
 ments on, 173 
 
 TROUBLE gear in lathes, 131 
 4- Drilling machine feed gear, 200 
 multiple, 203 
 
 Double gear radial, 204 
 
 — — slot-drilling, 206 
 table, 199 
 
 — machines, 181, 198 
 
 — tools, 187 
 
 TjtACE lathes, 146 
 
 plates for lathes, 136 
 
 Peed, Calculation of, in wood-plan- 
 ing, 35, 40 
 
 — for circular saws, 54 
 Frame saws, 46 
 
 Friction between tool and metal 
 surfaces, 78 
 
 CJ.AP lathes, 145 
 
 ^4 General characteristics of 
 steel, 225 
 
 Grinding wood tools, 14 
 Guidance of drilling-point, 192 
 
 TT ALF-LONG plane, 26 
 Hand planes, 24 
 
 Hardening and tempering tool steel, 
 228, 232 
 Hatchet, 11 
 
 Headstocks, Fast and loose, for 
 lathes, 123, 127, 133 
 Hollow mandril lathe, 170 
 Horse-power for wood-sawing, 56 
 Hot iron saws, 58 
 
 JNSERTED teeth in wood-saws, 50 
 
 T ACK plane, 26 
 ^ Jaw chucks, 139 
 
 T ATHE work, Geometrical char- 
 acter of, 106 
 Lathes, 105 
 
 — Back steady rest, 169 
 
INDEX. 
 
 2 39 
 
 Lathes, Boring col ! ar, 171 
 
 — Break, 146 
 
 — Capstan tool-rest, 170 
 
 — Centre-point, 124 
 
 — Cutting tools for, 150 
 
 — Double gear, 131 
 
 — Driving and chucking, 134 
 
 — Experiments on cutting pressure 
 on tools, 173 
 
 — Face, 146 
 plates, 136 
 
 — Fast headstock, 123 
 
 — Function of lathe-bed, 143 
 
 — Gap, 145 
 
 — hand and power mechanism, 107 
 
 — Headstock bearings, parallel and 
 conical, 127 
 
 — Hollow mandril, 170 
 
 — Jaw chucks, 139 
 
 — Loose headstock, 133 
 
 — Screw-cutting feed motion, 118 
 
 — Slide-rest, 112 
 
 — Springing of the tool, 160 
 of the work, 167 
 
 — Tools for wood- turning, 109 
 
 — Tool-holders, 162 
 
 — Tool-rest for metal-turning, 110 
 for wood-turning, 108 
 
 — Treble gear, 148 
 
 — Wheel, 149 
 Lead bath, 232 
 
 Lubrication and cooling of tool 
 edges, 81 
 
 — in drilling, 197 
 
 Planes, Jack, Try i ug, Smoothing, 
 American, 24 
 
 Planing Machines, Classes of, 32 
 
 Cutting action in, 71 
 
 Fixture of tool or work, 70 
 
 — — for metal, 70 
 for wood, 32 
 
 Smith and Coventry’s improve- 
 ments, 104 
 
 — — Systems of driving, 94 
 Power required to pare wood, 19 
 Punching and shearing machines, 
 
 210 
 
 — Error in calcu’ation of strength 
 of punches, 223 
 
 — Mode of rupture in punchii g, 221 
 in shearing, 221 
 
 — Multiple punching machine, 220 
 
 — T weddell’s hydraulic, 218 
 
 — Whitworth’s driving gear, 218 
 
 Q UICK return in planing n a- 
 chines, 89 
 
 T>AKE top and bottom in lathe 
 -*-* J tools, 152 
 
 Bansome and Co.’s wocd-planing 
 machine, 40 
 Batchet braces, 209 
 Beversible tool- holders for planing 
 machines, 92 
 
 lyr ANUFACTUBE of tool steel, 226 
 -L'-L Milling cutters, Cutting ang i es 
 of, 68 
 
 face-plate, Chuck for, 67 
 
 Sharpening of, 66 
 
 ■ Smith and Coventry’s Im- 
 
 proved, 69 
 
 — n achines, 56, 62 
 
 Cutting speed and feed, 64 
 
 - — Traversing headstock, 68 
 Morse Twist Drills, 191 
 Mortising Chisel, 9 
 Moulding blades, 42 
 Multiple punching machine, 220 
 
 T)ABING action, Theory of, 16 
 Paring chisel, 13 
 Penknife, 12 
 
 Pitch of chisels in wood-planing 
 machines, 38 
 
 Planes, Difference between wood 
 planes and paring chisels, 30 
 — guidance of, 27 
 
 CAVING of timber and of power 
 ^ in sawing, 43, 44 
 Sawdust space, 51 
 Saws, 43 
 — for iron, 58 
 
 Saw-teeth, 46 
 
 Screw-cutting in lathes, 118 
 Scroll saws, 46 
 Setting edge tools, 15 
 
 — saw-teeth, 47 
 Shaping machines, 96 
 Shearing machines, 210, 214 
 8ide-rake in lathe tools, 157 
 
 — tools for lathe work, 160 
 i Silicon in tool steel, 217 
 
 [ Slie.e resr, 1 j 2 
 Slot-drilling, 2C6 
 Slotting machines, 99 
 
 Mode of driving, 101 
 
 Table and feed mot] on s, 102 
 
 Smoothing plane, 27 
 
 Speed of cutting in circular saws, 51 
 
 — for cutting wood, 32 
 Special brands of tool steel, 
 
 [ Springing < f lathe tools,, x60 
 j Steady-rest, 169 
 
240 
 
 CUTTING TOOLS. 
 
 Suddening cooling of tool steel, 
 Effects of, 229 
 
 rnEMPERING, 232 
 ^ Tempering colours, 233 
 Tenoning machines, 42 
 Tool-box for planing machines, 86 
 — -holders for lathes, 162 
 
 for planing machines, 84 
 
 Beversible, for p'aning ma- 
 chines, 92 
 
 Tool-rests for lathes, 103, 110, 112 
 
 Tool steel, 225 
 
 Treble gear in lathes, 148 
 
 Trying plan», 26 
 Twist drills, 191 
 
 TTELOCITY of cutting in wood- 
 * planing, 32 
 
 Vertical spindle Wood planing ma- 
 chines, 33 
 
 TWATEK, cooling of steel by evapo- 
 ** ration, 231 
 
 Wedge action in cutting tools, 8 
 
 Theory of, 3 
 
 Wheel-lathes, 149 
 
 CASSELL AND COMPANY LIMITED, PI'LLE SAUVAGKE WORKS, LONDON, E.C.