dotnell XDlniverstt^ XibraiMp OF THE 1Rew ^otk State College of agriculture A>«:i,-^Ul>b >h\jnI\\"2l. Cornell University Library T 353.W78 Notes on practical mechanical drawing, wr 3 1924 003 646 209 Cornell University Library The original of tiiis book is in tine Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924003646209 NOTES ON Practical Mechanical Drawing WRITTEN FOR THE USE OF STUDENTS IN ENGINEERING COURSES BY VICTOR T. WILSON, M. E. PROFESSOR of DRAWING AND DESIGN at tt. MICHIGAN AGRICULTURAL COLLEGE. EAST LANSING, MICHIGAN AND CARLOS L. McMASTER. C. E. Formerly ASSOCIATE in GENERAL ENGINEERING DRAWING ai the UNIVERSITY OF ILLINOIS URBANA. ILLINOIS FOURTH EDITION REVISED AND ENLARGED PUBLISHED BY WILSON & McMASTER, EAST LANSING, MICHIGAN. NINETEEN HUNDRED AND TEN S ^q.•^^b5 OOPYBIQHT, 1909 BY V. T. WILSON AND C. L. McMABrsB MPLKY a, SBAY, PBINTBBB LANSING, MIOH. PEEFACE This book is a collection of notes intended to furnish, the basis for a course in elementry mechanical drawing, so arranged, it is thought, that the teacher may have the widest latitude in his choice of sequence of subjects. Since its first edition, two years ago, the book has been rearranged with this particular point in view. It has been thoroughly revised and also enlarged by the addition of more explanatory matter and illustrations in orthogra- phic projection, by a chapter upon isometric and oblique drawing, and by a number of exercises in working draw- ings from sketches. The usual geometrical drawing has been reduced to a minimum; it has been included, not for its value as exercise in drawing, but for the knowledge conveyed upon constructive processes useful in the science. Latest practice in teaching drawing shows the influ- ence of utilitarianism. The aim of a mechanical drawing is to record useful facts; useful facts, therefore, are used as exercises from the beginning of the study. The theo- retical or geometrical science forms but a very small part of the knowledge required in the subject and, where courses in drawing are necessarily short, the maximum of practical information is aimed at. The course here out- lined uses working drawings as exercises almost from the very beginning. Of course, the actual subject, from which to draw, is .most to be desired, but it is not always available or practicable, particularly in the beginning and with large PREFACE. classes, therefore numerous working drawing sketches are presented as problems. Again, nothing can take the place of the personal guidance of the teacher in inculcating good methods of work, but large classes make the individual direction by the teacher difficult, hence, minute directions are given upon the care and use of tools and methods of working to aid the teacher and student. And it may be stated, from their experience, it is the conviction of the authors, that, where good methods and system in working are insisted upon from the beginning, the quality of the the product is greatly improved. This theory is opposed to the one that practice only, together with quantity, makes perfect. Of course it is expecting a great deal of the student that he grasp all the practical points given in a short course, but, here again, experience has verified the con- viction that it is possible and especially where the exercises are made to be of interest, for where interest is aroused individual initiative will do the rest. Quotations have here and there been made from standard works on drawing, and acknowledgment has been given in each case. V. T. Wilson, C. L. McMaster. TABLE OF CONTENTS. CHAPTER I. LETTERING. Kinds of letters in common use. Lettering in design. Variations in width, lieigtit, etc. Stability of letters. Tlie Roman and Gotliic capitals and small letters and numerals. Off-hand lettering. The Old Roman and Roman-Gothlcletters. Titles. Bills of materials 1-18 CHAPTER II. ORTHOGRAPHIC PROJECTION. Drawing as a science. Befinitlon of projection, and the coordinate planes. The two planes folded one upon another, forming four dihedral angles. The projections of a point discussed. The projections of a limited line, plain figures and solids. The end plane. Any oblique plane of projection. The circle in projection, any curve in general. Dif- ference between first and third angle projection. Problems 19-38 CHAPTER III. ISOMETRIC AND OBLIQUE DRAWING. Definition of isometric drawing. The difference between isometric draw- ing and Isometric projection. The conditions of isometric projection described. The treatment of curves. Obliaue projection descrlbed___39-4S CHAPTER IV. THE USB OF INSTRUMENTS. Practical points about drawing materials and instruments. Peculiarities of tracing cloth. Stretching of paper. Drafting machines. Care and handling of tools. Use of each tool for its proper purpose and keeping them handy. Detailed directions in use of ruling pen, how to avoid errors with and how to sharpen. Directions for penciling drawings, and care of pencil. System of penciling. Detailed directions for ink- ing drawings, character of lines to use. System of inking. Gleaning drawings. Handling compass, dividers and bows. Use of irregular curve — 44-65 V : TABLE OF CONTENTS. CHAPTER V. WORKING DRAWINGS. OrthograpUc projection and working drawings. Of what a set ol working drawings consists. Violation ol rules of orthographic projection In working drawings. Development and arrangement ol a set ol working drawings. Drawing to scale, and directions In the use ol. Sections. Standard section lining. Some practical hints. Rules ol projection violated In sections. Dimensioning. Practical hints In dimensioning. Dimensioning ol certain features. Notes lor finish. Markings on drawings. . Checking. Conventions in common use. Tracings. V and square threaded screws analyzed. Peculiarities of the curve. The V threaded screw. The conventionalization lor threads. TheWhltworth standard. The U. S. standard. Other forms of thread. The hexagonal form ol bolt heads- Names ol various bolts and screws. Rivets. General directions lor the treatment of problems. Twenty-three miscellaneous problems in working drawings _. 68-152 CHAPTER VI. GEOMETRICAL DRAWING. Geometrical drawing vs. mechanical drawing. To draw a tangent to an Irregular curve at a point ou the curve. To rectify an arc ol a curve or of a circle subtending a small angle. To draw an arc of given radius tangent to two given obliaue lines. The conies. To draw an ellipse by the focil method, by the method of the trammel, and approximately with the compass. To draw a parabola by means ol the focus. To draw a hyperbola by means of Itafocii, by the rectangle method. The cycloid. To construct the cycloid. To construct the epicycloid, the hypocyclold. To draw the Involute of a circle 158-172 CHAPTER VII. MACHINE SKETCHING. Sketching as an accomplishment of the engineer. Scale in sketching. Pro- portion in sketching. The problem in hasty sketching. Treatment and arrangement ol views. Practical points about sketching 173-177 APPENDIX. Blue print process and reproduction _ 179-180 INDEX - -- 181-186 NOTES ON PRACTICAL MECHANICAL DRAWING. CHAPTER I. LETTEEING.* 1. The lettering, vrhich the draftsman, in practice, uses most, is a rapidly executed statement, on a drawiug, in what is known as an off-hand style. It is a very simple letter which he learns, with practice, to do in ink without any preliminary pencU layout, beyond the limiting lines, to show the height of the letters. Before the beginner, however, can hope to attain a proficiency, in even the free lettering mentioned, he should study carefully letter forms as they have been gradually developed through the centuries, to what are called standard proportions. 2. Good lettering is not mechanical, but is good design. The straight edge, compass or other tools, have no place in the drawing of letters, beyond the making of the limiting lines just mentioned. Good design requires : (a.) Simplicity of style, instanced in the advertisements con- fronting us so commonly every day. (&.) Uniformity of •The matter upon lettering la extracted from "Free-hand Lettering," by Victor T. Wilson, by kind permission ol the publishers, Messrs. John Wiley & Sons. 2 NOTES ON PRACTICAL MECHANICAL DRAWING. effect, as the units in any design are distributed through- out the area to be covered. The letters, that is, should appear to be of the same height, the same general size, and the spacing should also appear to be uniform. These things can only be properly attained through judgment and taste combined with accuracy of eye in the detection of small difEerences. 3. Letters actually vary in width, because those which do not fill their rectangle of space, as the H does, look smaller if they are made of the same width as the H. They must be made slightly wider than the normal letter; for example, the letter A must be spread at the base, because it only occupies half the rectangle of space allotted to it; likewise the B, C, D, etc., must be widened, each to a dif- ferent degree. The exceptions to this are the L and the F, which are made narrower than the normal letter. 4. Letters actually vary in height, because, where a letter touches its upper and lower limits only by tangency, it would look shorter than the H or N, if made tangent to them; it must be made to slightly exceed both limiting lines, as the C, G, and 0. " Letters such as A, V, etc., should also exceed the limits, if their angles are made sharp; to overcome this they are often somewhat blunted 5. Letters are modified to produce an effect of stability, that is, those letters that have upper and lower parts, dis- tinctly separated, appear more stable, and of good form, if the lower section is made larger than the upper ; for example, the lower lobe of the B, the spread of the arms LETTERING. ^ of the X, the K, the lower horizontal stroke of the E and the Z; the lower curve of the S, also, is made larger across and higher than the upper. 6. Letters are further varied in their several variations; that is, when combined into words, slight modifications can be introduced, here and there, to advantage; for example, an L, just preceeding an A, can be made nar- rower than if it were followed by an H or were at the end of a word or a line. To mechanically figure out all these modifications simply spoUs the spontaniety of design; they must be the result of judgment applied in each particular case. Hence, the student should not regard the modifica- tions shown on the plates as having any value, beyond suggestions to aid in the formation of correct perceptions. 7. A knowledge of free-hand drawing is essential to facility in lettering because the eye is then trained to see form and to judge of effects ; moreover lettering should be developed much as a free-hand drawing is developed, by first getting a broad, simple effect and proceeding to the details gradually in the order of their importance. 8. Figure 1 shows the upper case Roman letter, in a standard form. Upper and lower case are terms used by printers for capital and small letters, so named, because the type representiag them are placed, respectively, in the upper and lower part of the type case. The Roman letter has no really standard form, in which exact proportioning is attainable. The ancestors of this letter had a very different form from that we now find NOTES ON PRACTICAL MECHANICAL DBA WING. hh • o O 1 10 J lO 1 1 |i" \l i 1 -01 7 lO 1 1 1 M I'l .1 I LETTERING. in the printer's type, or in modern good examples. It has been modified and changed by different authorities, we cannot point to any one illustration of a perfectly correct Eoman type, but to many, varying slightly in some cases, quite radically in others. This letter is a refinement of an imitation of the strokes of the quUl used by the early scribes. It is nearly square, in fact was square, in its early forms. Referring to the figure, the heavy stems are made a normal width of one unit, the height of the letter being divided into six parts called units. The numerals at the bottom of each letter also stand for units. If the body of a letter varies in thickness, as the B, C, Gr, etc., the maxi- mum width, at the middle, is slightly greater than one unit, the S and U being exceptions. The large spurs on the E, F, L, T and Z do not join the body of the letters like the serifs, by tangent curves; they meet the horizontal strokes abruptly. The mid-horizontal strokes of the B, E, F, H and E are put slightly above the center of the space, to lend an effect of stability, the P is an exception to this. The inner and outer edges of the curved parts of letters, as B, C, O, P, and the upper part of the letter R, are formed by arcs of regular curves with vertical and horizontal axes; the inner ones approach the outer tangentially. The vertical axes of the outer curves are slightly larger than their horizontal ones, except the U. The difficulties of drawing the S, common to beginners, may be materially lessened by using an O, of the same proportions, as a basis in sketching. NOTES ON PRACTICAL MECHANICAL DRAWING. o •a 1— ( M O is Q o LETTERING. 9. The small letters are shown in Fig, 2, to harmonize with the capitals. These may be divided into three classes, ascending, descending and short letters. The ascending, except the 't,' have a height equal to the capitals, and the descending are the same in total length. The height of the short letters, relative to the others, is not fixed, but they generally vary between about one-half and two-thirds the height of the capitals. In the figure they are six-tenths. The width and height of the small letters are related to each other, in the same manner as the corresponding dimensions of the capitals. The height of the short letters is divided into six parts, each a unit for both the width of the letter and the weight of body. The same peculiarities, as to variations, which occur in the capitals, also occur in the small letters. FlQUBii No. 3 4,IL4U [.-4 5-11—4-^ L-4iJ \^4^-i l-4i-Jl-4i-J U4.i-J lO. The Roman numerals are shown in Fig. 3. They can be made the height of the capitals or slightly shorter, according to taste. They have the same peculiarities, as to variation in height, width and weight of body, that the letters do. NOTES ON PBACTIOAL MECHANICAL DRAWING. o 1—1 W ^ Eh 6 O m 2 (^ Q O lO n J '1 a J 1 in m z^^™" lO J _i •P «3 !J lO LETTERING. 9 11. The Gothic or uniform body letter, as shown in Fig. 4, is one of most common use by draftsmen, either as a heavy body or a light one made by a single stroke of the pen. For a letter to appear as heavy as the Roman, the Grothic is made slightly thinner in the stems. Note that the ends of all letters are cut off perpendicularly to the outside edge of the body. It has the same varia- tions as noted in the Roman. 12. Off-hand lettering is shown in Fig. 5, in the simplest and probably the most common style, the Gothic. It should be made directly with the pen, the limiting lines only being ruled ; this last, the beginner should never fail to do. It has been found that a certain system in strokes produces the best results and such an analysis is given in the upper rows, showing several ways of doing it, any one of which is good. It requires a great deal of skill to handle off-hand lettering satisfactorily, and the beginner should not be discouraged at the large amount of practice work necessary to attain it. Cultivate a steady, uniform' stroke, as far as possible, towards the person, as a basis for these letters. It is impracticable to depend upon patching unsatisfactory lines. Rows 4 and 5, of Fig. 5, are the same letter as that in the first three rows, and is of a standard proportion and quite common size. Rows 6 and 7 are the same letter inclined. The inclination should be about 20° from the vertical ; it can be somewhat greater, but it should not be less, else it is apt to look like a poor attempt at the vertical 10 NOTES ON PRACTICAL MECHANIOAI, DRAWING. ^ S ^ _3^ 5i> /:> I— I— ^ ^:^ e O 00 Co r CO o •^1 tl It — ■ w\*' f|tl It ^^-\J' — w"*^ -^ ^/ •— X 5 §■ ^^ ^v'o fit) — \ ^ (vitLl[!2_ ^,, LL_! ^ pT '3' r\ CD > _Q D -^ ^^ r 8 o C3 T^ ^ ^ ^ ^ ^ •^ ^ LETTERING. 11 style. An important point to note, in the inclined style, is that V and W, etc., are so inclined that the bisector of the angle of the sides has the direction of the main stems of the other letters. Also, note that the O forms, if accur- ately made, are inscribable in a parallelogram, whose inclined sides have the direction of the main stems of the other letters; that is, the axes of the oval forms do not have exactly this direction. The kind of pen used for this letter will determine the weight of the strokes. At first it will be found difficult to make a continuous straight stroke of uniform weight; to aid in doing this; first, hold the pen so that the plane of the pen axis, and the line to ie made, are perpendicular to each other, then touch the paper, pressing the nils of the pen apart to the proper width before starting the stroke; after starting, continue motion uninterruptedly until the end, and lift the pen just an instant after stopping motion, else the line will taper to a fine point. If a lump accumu- lates upon either end of the line, it can he overcome by carrying less ink in the pen, combined with a briefer hesita- tion at beginning and ending. Whole arm motion is found helpful. Fig. 6 shows some other styles of off-hand lettering. Rows 1 and 2 are based upon the Grothic and have its characteristics, mainly, while rows 3 and 4 show a free style appropriate to architectural drawings. The propor- tions of letters used depend upon the space allowable for them; however, a broad letter finds more favor than a narrow one. It is certain that increasiug the breadth of a letter increases its legibility more than a corresponding and proportional increase in height. The expanded form is shown in several places later on. 12 NOTES ON PRACTICAL MECHANICAL DRAWING. M >- X o- ^ % > — — OJOJOJOJCO 'st' — "0 OS . . to QQ < o ^-^ o ex < &, o « 6 (J O « i CO 10 CX) CO ^ ^ CO •0 QQ CO CO C\J 0) CO CO ^ ^ CM X X (0 X (^ X CM 5 X nj X 00 X X X CM X 0) 1 1 1 1 ^ _^ M CM — — fO LETTERING. 13 13. The desirable size for an off-hand letter depends upon circumstances; if it is made, for example, from one to one and one-half times as wide as it is high, the short letters may be one-sixteenth of an inch in height, as it is made narrower the height must be increased, for equal legibility, in greater proportion. The usual sizes may be said to vary between one-sixteenth and one-eighth of an inch. 14. The desirable pen to use, may be a hall pointed pen, if fine, or a Gillott's 303; the latter should be worn down a little to produce the most satisfactory results. The falcon pen is also a good one; any pen of medium stiffness, will do which will make the desired weight of stroke without patching. In wiping the pen, be careful not to press the nibs too far apart against the wiping cloth, they are apt to take a set and spoU the spring in the pen. In filling the pen, use the quill attached to the cork, in preference to dipping the pen in the bottle, as the handle is apt to get ink on it. Clean the pen every time it has to be filled and keep the ink bottle closed, tight, except when filling pen. 15. The old Roman letter is shown in Fig. 7, rows 1 to 5. It is an attempt to preserve as much as possible of the early type of the Roman as is consistent with modem requirements in letters. It is a beautiful form and is increasing in popularity; it is a much freer letter than the conventional Eoman, and, being free, it is not found in such a uniform style, there are more variations indulged in. The letter here shown is a very careful compilation from the best authorities. 14 NOTES ON PBACTiCAL MECHANICAL DRAWING. uz^ LETTERING. 15 16. The Roman-Gothic letter is shown in rows 6 and 7. It is a very popular form of letter today, being a combina- tion of two styles, as its name implies. It probably is preferred, because of its heavy face and consequent ease of construction. 17. Titles to drawings are placed, commonly, in the right-hand lower corner and consist of (a) the designation for the drawing, (b) the firm for whom it is made, (c) the scale, (d) the date, and frequently a set of items such as 'checked by,' 'corrected,' 'traced by,' etc. In designating titles to drawings, the fundamental re- quisite is appropriateness ; simplicity in style is an adjunct to this for working drawings, and the simplest letter is the Grothic. Titles are generally made wholly in capitals, although there is no rule to control this. If small letters are used, it is, generally, where minor matter has to be compressed into small space. It is well to lay out the whole title in a design with a very simple contour shape, and give a suggestion only of the weight of the different lines. Fiad the middle or axial line, of the title and sketch in on both sides of it. Fig. 8 shows a method of laying out a simple title. Make minor connectives small and, if short, preferably use an expanded letter. The title should look equally well if all connectives, as 'made by,' 'for,' etc., are left out. Use only a few styles of letters in a title, not more than three, preferably one, and do not depend upon 16 NOTES ON PRACTICAL MECHANICAL DRAWING. 8 < (re:! Qh— I— o o U6 =!LiJ D LUO ^ I- I' o CO CD >- or < I u u Q i t^ (r: Q< o^> -DQ 01 Q < Q^ O 0- z < o a: y < r-. dl al 5- dl 5. JZ — D C c_ Q.CO r- T=^ at T, • ^^ cIl ^7 J (J u (0 >- V, , < ^ -v X 1' r' i t i. . ^ 1 • 1 Cl 1^ L ~ I. J. :j c " z < -; c^ ^(0 c "' => b ^ J? q3 !- ,' • ' n (-1 ,0 — :§-a-S^ ^ O ■^O ^O ££ o. D^ ro § P^ I -D c -C q5 5 c liJT5 - o o UJ Q- Q a: u I h o: L y < 5 < 08 It: Q. I h >■ "D ,0> 0°- o Q a: OQ CL < CO LETTERING. 17 FlGtTBE No. 9. PLAN OF PROPOSED EXTENSION of the WATER SUPPLY SYSTEM of the CITY OF LAWRENC 'Showing the connections with existing mains. Prepared under {he direction of Chas. H.Hin City EngV. 1907 jScole *^ Feet (O^ O^ zoo 300 Zoo LOCATION SURVEY \m PROFILE FDR XME MEMPHIS iRANCH nr THE —J ♦ s- Prepared by the Engineering Department Nashville — Tenn. June 1908 Scale of Feet 18 NOTES ON PRACTICAL MECHANICAL DRAWING. variety of treatment but upon harmony, neatness, com- pactness and legibility. The two titles of Fig. 9 illustrate the style common in civil engineering and map drawing. More painstaking work is characteristic of civil engineering practice in lettering than is found in other professions. The second title is of the simplest style. The first is more difficult, being the Eoman letter throughout. 18. Combinations of Roman and stump letters, either verticle or inclined, are found in the majority of titles on maps of all kinds, including municipal maps. The difficulty of construction limits its field to the higher class of finished drawings. The letter may also be executed very acceptably off-hand. Such titles are very common in engineering practice. The stump letter is shown in the last two rows on Fig. 5, the capitals, for which, are the inclined Eoman. 19. A bill of materials is often attached to drawings. It may be in a corner of the sheet, and usually the lower right-hand corner, above the title or it may be upon a separate sheet or sheets, if it is very extended. It is made in off-hand lettering, neatly executed. Its contents will be further discussed in Chapter IV. The lower part of Fig. 6 gives examples of such tabulation. CHAPTER II. OETHOGRAPHIC PROJECTION. 20, Drawing is the art or science of recording a person's impressions about things by a more or less accurate sug- gestion of form. It is a technical subject of great value to the engineer and architect, the graphical language with which they work and by which they convey their ideas to those who construct the things they lay out. It is the language, moreover, understood by all nations, having for its purpose the complete representation of any object or structure to be erected. All drawings may be divided into two general classes. (a.) The drawings of objects as viewed at a finite distance, (b.) The drawings of objects as viewed at an infinite distance. The first of these is called perspective. The point of view at a finite distance is called the center of projection. It is as if the eye were at the point and the drawing of the object was made upon a transparent plane placed between the latter and th6 center of projection, that is, projected upon it from this center by lines from the center passing through all points of the object. It is a kind of drawing that is found in pictures. In the second class the center of projection or the eye is theoretically moved to an infinite distance, that is, the projecting lines, from the object to the plane, become parallel. This, in a certain form of drawing, is what is called orthographic projection. 20 NOTES ON PBAOTIOAL MECHANICAL DRAWING. Things are constructed and manufactured from draw- ings made according to the principles of the second kind mentioned, or orthographic projection. They may be made free-hand, that is by sketches, or they may be made by careful mechanical drawings. A mechanical drawing, used for the purpose of con- struction, then, consists of one or more views, made according to the principles of orthographic projection; in addition to which the sizes of parts are clearly set forth by dimensions, notes or other symbols that are required to accurately construct the same. No matter how simple is the subject to be constructed, an accurate and comprehensive and unmistakable drawing should be made of it. The test of a good working drawing lies in the fact that the workman can make nothing out of the facts contained thereon than what was intended by the draftsman. The entire meaning should be clear beyond the shadow of a doubt. To choose the number of views . that this may be attained, to put on the dimensions which the workman will need in making the subject, is the problem of the draftsman. The needs of the workman should be constantly in his mind. 21, Orthographic projection is the science of represent- ing forms by projecting them upon two or more planes by means of projecting lines respectively perpendicular to these planes. The center of projection, from which the projecting lines eminate, is infinitely distant in a direction perpen- dicular to the planes of projection, and, since they pass through a common point at infinity, they are parallel. ORTHOGRAPHIC PROJECTION. 21 The 'coordinate planes of projection,^ is a term used to designate the three fundamental planes in common use, namely, a vertical plane (V) , a horizontal plane (H) , and FIQTJEB No . 10. a plane perpendicular to these two, known as the end plane, or profile plane (E or P). The vertical and the horizontal planes intersect each other in a Itae known as a 'ground line' (G-.L.) and each is indefinite in extent. Fig. 10 shows a picture as in perspective, of these aa NOTES ON PRACTICAL MECHANICAL DRAWING. several planes as they would appear if made of trans- parent material. 22. The V and H planes form with each other four dihedral angles, but, for purposes of representation on a drawing, it is necessary to conceive of them as being folded into coincidence with each other. When so folding, they revolve about the G.L. in the direction of the arrows shown, the H plane being revolved into coincidence with the V plane, or the latter revolved into coincidence with the H plane so that the 2nd and 4th angles, as designated in Fig. 10, close up to 0", while the 1st and 3rd, unfold to 180" . The revolution of the end or profile plane will be discussed a little later. *23, A is a point in space, as shown in Fig. 10 in the first dihedral angle. Its projection on the V plane is the foot of the perpendicular to the V plane Aa'. Likewise its projection on the H plane is the foot of the perpendic- ular to the H plane Aa. If perpendiculars are dropped from a' and a respect- ively to the G.L., they will intersect the G.L. in a point, and the four lines together make a rectangle. 24, The distance of a' from the G.L, shows the distance of the point from the H plane and the distance of a from the G.L. shows the distance of the point from the V plane. When the V and H planes are folded into coincidence, as in Fig. 11, the perpendiculars, let fall to the G.L. from a' * The notation, which will be used, Is as loUows : — a', 6', c', etc., stand for the vertical projections of points, and a, b, c, etc., stand for the horizontal pro- jections of the same points. ORTHOGRAPHIC PROJECTION. 23 and a, become one and the same line perpendicular to the G.L., and it is in this form that orthographic projection deals with points, lines, etc. FlGtTBB No. 11. b V plane above H. G. H plane In Iront of V. al Also H plane back of V. . Also V plane below H. b' 25. The projections of a point in the 1st angle, 2 inches from V and 3 inches from H, in V projection, would be placed 3 inches above the G.L., and in H projection would be put on a perpendicular to the G.L. through the V pro- jection, a distance of 2 inches below the G.L. If it were required to show the projections of a point which was in the 8rd angle, H inches from V, and 4 inches from H, the V projection would be placed 4 inches below the G.L., and on the same perpendicular to the G.L., through it, would be placed the H projection 1^ inches above the Gr.L. If a point is in one of the co-ordinate planes, its corre- sponding projection is in the G.L,, that is, if a point is in the V plane, its H projection will be at the intersection with the G.L. of a perpendicular through its V projection. If a point is in both co-ordinate planes, it must lie at their 24 NOTES ON PBAOTICAL MECHANICAL DRAWING. intersection, i. e., be in the Gr.L,, and both projections coincide with each other, and with the point itself. Further discussion of the principles will be confined to forms in the 3rd angle exclusively as this is more common in practice. 26. Lines are projected by projecting points on the line; if straight lines, the projections of two points will locate the projections of the line, and designate the position of the line in space with respect to the co-ordinate planes. Figure N o. 12. Fig. 12 shows the several projections of a limited line and also embodies all the different positions which a line can have with respect to the co-ordinate planes in the third angle. A B is oblique to both V and H, since the distances of A from both V and H are different from those of B. CD is parallel to V and oblique to H because the distances of C and D from V are equal; JK is perpendic- ular to V since the line connecting j and k is perpendicular to the G.L., and coincides with the projecting line of both J and K on V. NO lies in both H and V, i. e. in the G.L., and both projections of N and O, respectively, coincide with each other. This group of projections may OBTHOGKAPHIC PROJECTION. 25 be called, appropriately, the alphabet of the straight line in the 3rd angle. If a line is parallel to a coordinate plane its projection on that plane will show, (a), the true length of the line, and (6), by its angle with the G.L., the angle the line makes with the other or corresponding coordinate plane. 27. The projections of a plane figure are obtained by projecting separately points in the perimeter of the figure and connecting the projections by lines. If the figure is composed of a curve or curves, the projections of a con- venient number of points of the curve are connected by smooth curves. If the figure is composed of straight lines, only the vertices of the figure, or meeting points of the edges, need be projected. FlGITBE No. 18. m 1 b g . C "^^^^ k - a' A a' / ^ k' d' / "' f I' d e'^r Fig. 13 illustrates the projections of a plane rectangular figure in different positions in the 3rd angle, (a) when it is perpendicular to H and oblique to V, with two edges, AB and DC, parallel to H, (6) when it is perpendicular to V, and inclined to H, and, (c) when it is oblique to both H and V, with two edges JK and ML, parallel to both R and V. 26 NOTES ON PRACTICAL MECHANICAL DRAWING. 28. A solid is projected upon the coordinate, planes by projecting points on the surface of the solid; if the solid has plane faces, these points are usually the vertices where three or more faces meet. The projections will be plane figures enclosing, by solid lines, the largest number of points and those edges, which are hidden by the surfaces of the solid, are shown dotted. FiatTRB No. 14. g'f er i' f 9' Figure 14 shows a cube in projection, [a) resting on the H plane with four faces perpendicular to H and two parallel to V; consequently, each edge of the cube is projected upon one plane its true length and upon the corresponding plane as a point, shown by the designating letters of its two extremities; (6) a cube resting with one face on H and four faces oblique to V; (c) a truncated hexagonal pyramid. The notation is self explanatory. OBTHOGRAPHIC PBOJECTION. 27 29. The end or profile projection of an object is shown in Fig. 15 in the third angle. The upper part gives a perspective of the conditions, the lower, the orthographic projection of the same. Note that the end plane is revolved about its intersection with the V plane and always away from the object. The arrow in the figure helps to show this direction. 30. Any plane may be chosen upon which to project an object; it need not be either vertical or horizontal, but may be oblique to both such planes. It is convenient in case it is desired to show surfaces their full size and shape that are oblique to V and H. The principles of projection are the same and the auxiliary plane, as it is called, is revolved about its line of intersection with V or H into coincidence with one or the other of the latter. Fig.. 16 shows the method of dealing with an auxiliary plane. The upper part gives a perspective of the condi- tions, the lower, the orthographic projection of the same. The auxiliary plane is taken parallel to the oblique or truncated surface. 31. The circle is projected by projecting points, and connecting these projections by a line, or smooth curve, as the case may be. It is a form of frequent occurrunee in constructive work and deserves to be thoroughly compre- hended. It is convenient to circumscribe the circle with an auxiliary square, putting 'this into projection and referring the points in the perimeter of the circle to it. 28 NOTES ON PRAOTIOAL MECHANICAL DRAWING. Fl GTJEE No . 15. c b Ge \ \ \ 4 \ \ \ \ u ~"~~ \.° ^ ~-^v (^ dd d'c' H V EL 1 1 Ce ^ \, — vvQq ^° dk > ^« \ ^e OBTHOGBAPHIC PBOJECTION. FIGUEK No. 16. 30 NOTES ON PRACTICAL MECHANICAL DRAWING. FIQ0BBS Nob. 17, 18 AND 19. ^ i'f aV b'dV Fig. 17 shows the projection of a circle whose plane is parallel to H. In this position its projection on H will be a circle and, upon V, a straight line equal in length to a diameter of the circle, as GC. The points, at which the circle is tangent to the square, and those in which it cuts the diagonals, all lie in V projection, upon the line g' e' , as shown in the figure. Fig. 18 shows the same circle, revolved about the edge m n oi the auxiliary square, until its plane makes an angle of 60° with H. Since the plane is perpendicular to V. the angle of the line g' c' with the G.L. shows the angle the plane makes with H. The distances of the various points, in the perimeter of the circle, from the V plane, remain constant, hence the distances of their H projections from OKTHOGBAPHIO PBOJBCTION. 31 the Gr.L. is constant, and they may be transferred from Fig. 17 by parallels to the G.L. intersecting perpendiculars to the G.L., through the V projections of the points, respectively, as shown. Fig. 19 shows the same circle when its plane is oblique to both H and V. Its projections may be obtained from those of Fig. 18, by conceiving of the edge m n, of the auxiliary square, being revolved in a horizonal plane through any desired angle about the point m. Since the distances, of points in the perimeter of the circle, from the H plane are constant, the new H projection will not change its shape; and, for the same reason, the new V projection may be obtained by drawing perpendiculars to the new H projections of the points, and intersecting par- allels to the G.L., through the V projections of the points, in Fig. 18, respectively. If a circle is parallel to a coordinate plane, its pro- jection on that plane will be an equal circle, and its projection on the corresponding coordinate plane, to which it is perpendicular, is a straight line. In any other position, the projection of the circle is an ellipse, the proof of which properly belongs to the province of descriptive geometry. 32. Any curve in general may be projected by the prin- ciples already discussed, namely, by projecting, severally, points in the curve, or, where convenient, circumscribing the curve by a simple figure, such as a rectangle, and referring its points to the same. Worhing drawings, as before remarked, are made according to the principles of orthographic projection that 32 NOTES ON PRACTICAL MECHANICAL DRAWING. have been discussed. The V projection corresponds to the 'front view,' 'front elevation,' or simply 'elevation,' as the terms are variously used, and the H projection, to the 'plan.' The end elevation corresponds to the 'side view,' 'side elevation,' or 'end view.' The auxiliary projections discussed, correspond to various detail views of parts of a subject, which may have their edges or planes oblique to the principal coordinate planes upon which the subject may be projected. 33. The difference between 1st angle and 3rd angle pro- jection. For working drawings, the choice is open of either the first angle, or the third angle. In either the second or the fourth, the plan is quite likely to fall behind or in front of the elevation. If the distances of the eleva- tion and plan, from the ground line, are made to differ by a sufficient amount, this super-position can be avoided, but an equal difficulty is encountered, in not being able to distinguish which is second angle, and which is fourth angle, for the relation of plan to elevation does not determine it. In the first angle projection, the object is projected upon the vertical plane, from a center of projection, which is assumed to be on the same side of the plane as the object; this is also true of the horizontal projection. To be consistent, an end view of the object should be that obtained, by projecting it from a center on the same side of the plane as the object. For illustration : The view of the left hand end of an object would be placed on that plane, which was to the right of the object, and the view of the right hand end would be projected, upon the plane at ORTHOGRAPHIC PROJECTION. 33 the left. Now, if the same center is used, and an object is drawn in vertical projection, in the third angle, it will be projected through the vertical plane, for the center is on the opposite side of the plane from the object. Therefore, to be consistent, the end view should be obtained by use of a center, which is upon the opposite side of the plane from the object. If this is done, the view of the left hand end of an object wUl lie at the left, and that of the right hand end at the right. It is convenient to have this latter condition of affairs in a working drawing, because it conduces to legibility, and, in fact, it has been quite universally adopted. Care should be taken by the beginner not to be thoughtless in the use of either angle at pleasure, and in not mixing the two in a drawing. Figures 20 and 21 show the 1st and 3rd angle projec- tions of an object respectively. 34. * Problems in projection. (1.) Draw the projections of the following points. (a.) li inches from H, 1 inch from V. (&.) | inch from V and li inches from H. (c.) In V 1^ inches from H. id.) In H J inch from V. (e.) In the G.L. (2.) Draw the projections of the following lines, making either projection on V or H not over IJ inches long, {a.) Oblique to V and H, nearest end to V, i inch from it. (6.) Parallel to H and oblique to V. (c.) Parallel to V and oblique to H. (d.) Perpendicular to H, I inch from V. (e.) Perpendicular to V, and 1 inch from H. (/".) Parallel to both V and H, 1 inch from V *Tol)e drawn In 3rd angle projection unless otherwise directed. 34 NOTES ON PRACTICAL MBCHAUICAIi DRAWING. FiaUBE No. 20. ILLUSTEATING FIRST ANGLE PROJECTION. » ORTHOGRAPHIC PROJECTION. FiGtrliK No. 21. ILLUSTRATING THIRD ANGLE PROJECTION. 35 36 NOTES ON PEACTICAL MECHANICAL DRAWING. and I inchfrom H. (g.) Parallel to and equi-distant from V and H. (3.) Draw the projections of a rectangle of edges 1 inch X 1\ inches, (a.) Place it so that it is parallel to V and distant i inch from H. (ft.) Place it so that it is perpendicular to V and inclined at an angle of 45° to H. (c.) Place it so that an edge rests on H, its plane making an angle of 45° with H and the edge upon which it is rest- ing, at an angle of 60° with V. Note : —Place it first per- pendicular to V, at the required angle with H, and then revolve it into the final position, which will be oblique to both H and V. (4. ) Draw an equilateral triangle in projection of 1| inches on edge. So placed that an edge lies in V at an angle of 30° to H, and the plane of the triangle is at 60° toV. (5.) Draw a circle in V and H and end projection; the circle to be 2 inches in diameter, perpendicular to H, and making an angle of 60° with V. (6.) Draw the square pyramid, in projection, of dimensions as shown, the base parallel to and 3 inches from H, the edges of base at 30° and 60° respectively to Y. (7.) Draw the pyramid of problem 6 in projection showing also an end view, so placed that the plane of the base is perpendicular to V and makes an angle of 30° with the H plane. (8.) Draw the hexagonal prism of dimensions shown in V, H, and end projection, with a hexagonal base, rest- ing on the H plane, two rectangular faces parallel to V. (9.) Draw the hexagonal prism of problem 8, so placed that an edge of hexagonal base rests on H at 30° to ORTHOGRAPHIC PROJECTION. 37 6. jr^^T' V, with plane of base at 45° to H. Show V and H pro- projections. Project the same upon an auxiliary V plane which is perpendicular to the hexagonal bases. (10.) Draw the square prism shown, with square base resting on H, and rectangular faces at angles of 30° and 60° with V respectively. (11.) Draw the square prism of problem 10, placing it so that it rests on a short edge, on H, the edge mak- ing an angle of 60° with V, and the plane of the square base at an angle of 60° to H. Note:— Draw the prism first with two rectangular faces parallel to V, and then obtain the final position by projecting upon ar auxiliary or Vi plane at an angle of 60° with V. (12.) Draw the truncated hexagonal prism shown, so placed that a hexagonal base is in H and all vertical faces oblique to V. The plane of the top is at an angle of 30° 38 NOTES ON PRACTICAL MECHANICAL DRAWING. 10. 12. to H. Show the true shape of the section by projection on an auxiliary plane. Assume dimensions not shown. (13.) Draw the top, front and side views of block shown. Take the dimensions from the figure with the dividers, as they are represented in the picture their true size. 13. CHAPTER III. ISOMETEIC AND OBLIQUE DRAWING. 35. Isometric drawing, meaning a drawing of equal measurement, is one which shows form and correct dimensions, within certain limits, in one view. Ortho- graphic projection ordinarily requires two views of an object upon planes at right angles to each other, after- wards revolved into coincidence. A perspective drawing on the other hand, represents, by one view, the object as it would appear from some particular point, giving a pictorial representation, but not the exactness of shape, or the possibility of measurement required in a mechanical drawing. Isometric drawing combines both of these, and shows the three dimensions, length, breadth and thickness in one view and at the same time admitting of measure- ment. It gives a somewhat distorted appearance to objects, for that reason its application is limited to objects of simple shape. An isometric drawing may be derived as follows: If a cube is projected upon a plane, to which all of its faces are equally inclined, the re- sult will look like Fig. 22, and is an isometric projection of the cube.* All edges, as well as plane faces, are equally foreshortened; and, since FlGXTKE No. 22. 40 NOTES ON PKACTIOAL MECHANICAL DRAWING. this is true, all edges may be extended until they are equal in length to the edges of the cube, without affecting the proportional relations when we have an isometric drawing The principles of isometric drawing are derived from this treatment and are as follows : (a.) There are three lines called isometric axes, making angles of 120° with each other. These lines may have any position depending upon the position of the object, but usually those illustrated in Fig. 23. F IGVXH No. 28. (h.) These lines or isometric axes, represent lines which are at right angles to each other. (c.) Upon these lines, or lines parallel to them, the dimensions of length, breath and thickness are measured. All such lines are called isometric lines. Any other lines are 'non-isometric, and their position and length must be obtained by reference to some isometric lines. (d.) Parallel lines on an object are always parallel on the drawing. * Fig. 24 also shows by the dotted lines how a cube would look in isometric drawing. Objects, composed of non-isometric lines, must first be surrounded by, or referred to, an object of some ISOMETRIC AND OBLIQUE DRAWING. FlStTBK No. 24. 41 isometric construction, and the lines of the object are then referred to these isometric lines. For example, consider the treatment of a pjrramid, see Fig. 25. FlGUBB No . 25. 42 NOTES ON PRACTICAL MECHANICAL DRAWING. Curves in isometric drawings are obtained by locating a sufficient number of points with reference to some isometric lines, as in Figure 26. FIQTTBE No. 26 FIGTJKE No. 27. An approximate method for an isometric drawing of a circle is shown in Fig. 27. 36. Oblique projection is somewhat like isometric projection. In most cases its apparent distortion is greater than in isometric drawing, yet it possesses several distinct advantages; the principal one being that two dimensions are represented in their true direction as well FieiTBE No. 28. ISOMETRIC AND OBLIQUE DRAWING. 43 as size, giving one face in its true form as shown in Fig. 28. The principles of obhque projection are as follows: (a.) One face of the object is taken parallel to the plane of projection. On this face two dimensions are measured. (6.) All lines perpendicular to this face are made 45° lines on the drawing. On these lines the third dimension is measured its true length. (This is not strictly true oblique projection, but differs from it in a similar way that isometric drawing differs from isometric projection.) CHAPTEE IV. USE OF INSTEUMENTS. 37. Practical points about drawing materials and in- struments. A student's first lesson to learn, and a teacher's first duty, is to teach the proper use and care of tools. With this lesson learned, it should be possible for the beginner to work safely with the best appliances, and the best are none too good. It is the purpose now to say something about the difEerent tools and their proper care and handling. Drawing boards: The best drawing boards are made of well seasoned pine, of uniform grain, narrow strips glued together, the whole being finished at the two opposite ends at right angles to the strips by narrow pieces tongued and grooved and glued to the board, to prevent warping. In large boards of flrst-class construc- tion, battens are fastened to the back of the board, so as to permit of expansion and contraction of the board with changing tempera- ture, but not of warping. This is effected by fastening a batten rigidly at one point near the middle, and at two or more other points by screws, rigid in the board, but working in slots in the batten. In order to still further lessen the tendency of the board to warp, saw cuts or grooves are made about two inches apart, longitudinal of the strips of which the board is constructed, and of a depth of about half the thickness of the board. It is not absolutely necessary that all four edges of a board should constitute a true rectangle, they ought to be straight. Only one edge of a board, the left hand edge, should be used upon which to rest the T sq. head, the triangles should be used for vertical lines. The under side of a battened drawing board may conveniently be used to cut paper on, but it should never be done on the working USE OF INSTRUMENTS. 45 side, and care should be exercised that the working side and the edges of the board be kept clean and in all respects in good order. Tee squares are made in various forms. They should be of well seasoned wood of uniform grain. The blade may be sunk in the head or screwed on top and glued. A frequent source of trouble in T sqs. is that the part of the head just under the blade swells under the action of the moisture in the glue when it is made, becomes set, and causes the head to rock against the edge of the board when in use. The bulge in the head can be seen by placing a straight edge against it. An excellent form of T sq. is made of mahogany, with a very narrow edging of ebony. The latter is particularly hard, it relieves the edge by its strong contrast with the color of the paper. Sometimes a celluloid edge is used. This seems to have growing favor because of its trans- parency, permitting partial sight' of the work underneath. If T sqs. are large, they are tapered as before mentioned, so that the upper edge is the only one that can be used. Some T sqs. are made with a swivel head so that the angle of the blade can be adjusted, and they have their value. It may be said that one shouldbe in a large and well equipped drafting office, but that for ordinary use it is not necessary. Steel T sqs. are made, but are not favorities with draftsmen because of their weight and the danger of injury to the drawing by denting, etc. Triangles are made of the same materials as the T sqs., solid triangles, however, are not good as they will warp. Triangles are made also of vulcanized rubber and of celluloid. The former have the advantage of contrasting well with the color of the paper, but they have the disadvantage of being non-absorbent, consequently they transfer dirt from one part of the drawing to another and are apt to smear it. The inside edges of a triangle may have depres- sions cut in them to facilitate picking up from the paper. A 30° and a 60° triangle and a 45° triangle are the only two in common use except those especially made for mechanical lettering. Some other angles may be struck by using the triangles together and adding or subtracting their angles to get 15°, 75°, etc. Paper comes of various kinds and quality, suited to different kinds of drawing. A moderately heavy grade with smooth, hard 46 KOTES ON PKACTICAIi MECHANICAL DRAWING. surface is to be desired for mechanical drawings. A yellow or manilla paper is much used for pencil drawings, when the result- ing drawing is to be traced ; it is called detail paper. Bond paper has also come quite into use, and it has distinct advantages. The drawing is penciled and inked on the paper and from it blue prints can be readily made. Paper should, if possible, never be rolled, particularly rolled small as it cannot be satisfactorily flattened again. Tracing cloth is in almost universal use in drafting rooms for permanent drawings, as blue prints can be so readily made from it. Either the rough or the smooth side can be equally well used for drawing in ink. Frequently the original pencil drawing is made upon the rough side of the cloth and inked over. It fur- nishes a, very good surface for this purpose. The smooth side is impractical for pencil drawings but takes ink like a highly cal- endered surface. Special precautions, which will be mentioned shortly, have to be observed in working upon it. There is but one recognized grade and make of tracing cloth, the "Imperial." Stretching of paper, as it is called, is resorted to where any water color brush work is to be done. It consists of pasting the edges to the board and shrinking until it is quite taut. It takes a little experimenting to get facility in doing this, but every one ought to know how to do it when occasion arises, hence the following directions are appended. * "To stretch paper tightly on the board, lay the sheet right side up — which side is presumably the one which shows correct reading of the water mark when held to the light — place a rule with its edge about one-half inch back from each edge of the paper in turn, and fold up against it a margin of that width. Then thor- oughly dampen the back of the paper with a full sponge, except on the folded margins. Turning the paper again face up, gum the margins with strong mucilage or glue, and quickly but firmly press opposite edges down simultaneously, long sides first, exert- ing at the same time a slight outward pressure with the hands to bring the paper down somewhat closer to the board. Until the gum sets so that the paper adheres perfectly where it should, the latter * F. N. WlUson's Theoretical and Practical Graphics, p. 14, USE OF INSTRUMENTS. 47 should not shrink; hence, the necessity for so completely soaking it at first. The sponge may be applied to the face of the paper provided it is not rubbed over the surface so as to damage it. The stretch should be horizontal when drying, and no excess of water should be left standing on the surface; otherwise a watermark will form at the edge of each pool." The compass, dividers, hovr instruments and ruling pen consti- tute the simple, universal kit, and probably the majority of draftsmen have little else. Of course there are a number of other tools made, chiefly for special uses. These are not used univer- sally, however, because the time saved with a special tool is usually offset by the time consumed in handling and cleaning, for each special tool comes in generally for but occasional and brief use. Somewhat similar reasons explain why various special attachments to the simple kit are not popular universally, like hair spring legs in compass and dividers, spring catch ruling pens, micrometer adjustment to needle point, etc. Beam compasses are instruments to strike large circles, consist- ing of a needle point leg and marking point leg, each separate and adjustably mounted upon a bar of metal or wood. Every large drafting room is likely to have one for occasional use, but the individual hardly needs to go to the expense of one unless its use is demanded frequently. Follower pens, in which the pen is swiveled in the handle, are used to make irregular curves. The pen automatically adjusts itself properly to the ruling edge. It has but occasional use. A bow pen, made chiefly for special professions, has a fixed needle point leg with a marking leg sliding freely upon it. It is handy for striking a large number of circles of small diameter, but it is a tool for that special purpose. Dotting Wheels are instruments to do what the name implies, make dotted lines. They also have occasional use but are a trouble to care for and easily get out of order. Proportional dividers, consisting of double pointed legs, pivoted between the ends, and adjustable, so as to give a range of relation. 48 NOTES ON PBACTICAL MECHANICAL DRAWING. between the opposite angles formed, are a very useful tool indeed upon those rare occasions when a drawing is merely to be copied to a different size regardless of scale. Where scale is desired it is not safe as a tool nor is it much handier than the scale direct. A parallel straight edge is made which replaces the T sq. A rule, of the length of the board, is held at the ends by sliding on a wire cable and moves into parallel positions. Theoretically it is excellent but lack of sufficient rigidity is its chief drawback in the opinion of many. The protractor is a semi-circular disc segment of celluloid, bone or brass with degrees marked upon it. The center is marked on the straight edge of It. It has use where angles have to be struck of varying sizes and other than those for which the tri- angles can be used. There is a machine on the market known as the Universal Drafting Machine, which has very meritorious features. It com- bines the function of the T sq., triangles and scales, and, when specially adjusted, the protractor. It consists essentially of two straight edges with scales upon them and with a common point of attachment. They can be set rigidly at any angle to one another and the whole moved in any direction over the board through the medium of hinged arms, rigidly attached to the upper left hand corner of the drawing board. Straight edges, having any of the standard scales upon them, may be attached to the frame. There is also a Paragon Drafting Instrument accomplishing much the same purpose. It is attachable to a parallel ruler previously mentioned or it can be attached to a T sq. blade. The fixed center is the point of attachment and the ruling edges, two in number, can be swung around it at any angle, replacing tri- angles and protractor, and also having variously scaled edges. 38. Some practical points about and the care and hand- ling of drawing instruments. Drawings can he cleaned of dirt with the soft phable USE OF INSTRUMENTS. 49 erasers, the kneaded rubber, the sponge rubber or stale bread crumbs rubbed over with a cloth or with the hand. The liquid drawing inks will stand very little erasure with the pencil eraser without loss of blackness in the lines. To keep a drawing in good shape as the work progresses, cultivate early the habit of keeping the T sq. and triangles clean, using a piece of paper where possible over parts of the drawing not in immediate use, and, finally, keeping the hands off the work when they are not in active service. Be careful to use the tools only for the purposes for which they were intended. Violations of this are to be found in using the T sq. as a hammer to put in tacks, the dividers as compasses to describe arcs, sticking the divider points into the board so the dividers will stand alone, etc., all of which tend to injure the tools. The tools should he at all times handy. With the T sq. always on the board, the triangles above it on the board and other tools in predetermined places from which they can be picked up without much, if any, hunting, and while the eyes are engaged on the drawing, will conduce to rapidity and accuracy of work. Observe that the work- man in any craft will always lay a tool down when he is done with it, even temporarily, and moreover, he lays it down where it is the least trouble to find it again. Facility in the use of the ruling pen is eminently desira- ble, hence a few more practical directions are here given: — The greater care at all times should be exercised, the thicker the line used or the fuller the pen is with ink. The beginner should carry less ink in the pen than after he becomes an expert. When occasion arises to use the pen for long lines or many close together, with the least inter- 50 NOTES ON PRACTICAL MECHANICAL DRAWING. ruption for refilling, a considerable amount of ink can be carried in the pen if the following directions are observed: Head the pen to start, the point very close to but not touch- ing the paper; when ready, touch the pen to the starting point and instantly move on the line uniformly and rapidly, the more rapidly the fuller the pen. Stop and lift the pen in the same instantaneous way. These same precautions hold when making a very thick line with the pen; the thicker the line the less ink can be carried. In drawing lines to go from or to a heavy ink line or border still greater care has to be observed that the border does not draw the ink out of the pen and cause a blot. The FlGUBB No. 29. situation is illustrated in Fig. 29. It shows a series of lines close together where the edges of the lines are apt to break down and the lines run together. In cases of great danger, every other line or so may be begun late as shown in the figure and afterwards filled out when the ink dries. In patching these open spaces set the pen to make a finer line, matching only one edge of the line drawn, then by tilting the pen probably the requisite increase can be made if not with accuracy in one stroke, then in two or more; a line can be added to easily but it cannot be reduced in size, except by erasure first and then redrawing. If a pen fails to work it may be due to several causes (a.) It may be set so tight that the ink cannot flow out between the nibs. USE OF INSTRUMENTS. 51 (h.) The ink may have dried at the ends of the nibs, if not farther, and clogged the flow. The best thing to do is to at once clean and refill. The use of the blotter or a piece of paper drawn through between the nibs is to be deprecated. (c.) If the ink does not run down to the point, proper running may be facilitated by opening the nibs a little and shaking gently, over a blotter or something it will not injure if it blots, until the ink settles or drops out. The difficulty is caused by grease on the inside of the nibs. (d.) The pen point may be actually out of order. This of course demands that it be sharpened; but the pen should be tested for all the other difficulties first. An injured pen will either not mark at all or it will make a ragged line ; the line, moreover, may be ragged at one or both edges. If the pen is merely uniformly dull, it will refuse to make a fine line, the line will simply fail entirely if the nibs are brought close together. A pen can be sharpened and tested in the following manner: A fine oil stone should be used for this, an Arkansas stone seems to be prefeiTed. Bring the- nibs of the pen together as for drawing a very fine line, and hold for the rubbing at a small angle to the stone, 30° or less, and with the broad face of the nibs towards the stone. Eub to and fro in the direction of the handle with at the same time a slight rocking of the pen in order to round the point. If too pointed it tends to cut into the paper and will not hold sharpness so long. To test for sharpness, drag it on a piece of paper as if making a line ; it ought not to scratch roughly or glide too freely, but bite slightly, that is, resist motion. If it seems to act as it should, clean thoroughly and then try with ink. Properly sharpened, the pen should make a very fine black hair-line without breaking and a broad line of sharp edges, even if the pen is tilted five or six degrees out of plumb in a plane perpendicular to the ruling edge. Try for a broad line first with this test in order to 52 NOTES ON PRACTICAL MECHANICAL DRAWING. see if both sides are of equal length. If they are not, that side of the line at which the nibs are shortest will show ragged. If this test is successful and the line drawn is perfectly sharp and clear on its edges, test for fineness of line, by working from a wide line towards a narrow one. If it happens that the sharpening has pro- ceeded too far and the pen bites too deeply into the paper, or if one nib is slightly longer than the other, the pen may be dulled or the long nib worn down by rubbing it on the stone with a rotary motion when the broad nibs of the pen lie in a plane perpendicular to the plane of the stone. To determine the place of a line the ruling edge should furnish a rough approximation and the marking point the exact place. It is one of the important points in handling to be learned early. The nibs of a ruling pen, for example, being bowed, will touch the paper slightly beyond the ruling edge. If the pen is incorrectly tilted until the nibs touch the paper at the ruling edge, a blot is almost sure to result, for the ink will touch the ruling edge. It may sometimes happen, when a number of lines have to be drawn which run in a variety of directions, that waste of time is threatened in waiting for ink to dry. The ruling edge can be held slightly free of the paper and "over the wet lines by using the thumb and first or second finger as a cushion underneath it or one ruling edg:e may be rested on and shghtly overhanging another. In small work one triangle may be put with its open space over the lines to be drawn, and the other triangle rested upon it, crossing the gap. A method of inking will be shortly discussed which overcomes some difficulties of waiting for ink to dry. Errors in an ink drawing can be corrected so that the repairs are practically invisible. A knife will not do this unless used in conjunction with the ink eraser. In fact, cutting or scratching with a knife is so risky that it is safe USE OF INSTRUMENTS. 53 to adopt the custom of never using it except under extreme circumstances. If an error occurs, take up as much ink as possible with a blotter, but do not use it under any ordinary circum- stances to dry a liae because it pales the ink. Then use the ink eraser, rubbing rather lightly and rapidly, not in one direction or with one part of the eraser, but in all directions and changing the point of contact, because the rubber will heat and not work so well. Every vestige of the mistake should thus be removed, although it blurs a certain area around the error. Next clean oflf all the sand by using the pencil eraser. If the surface of the paper is very much disturbed it may be necessary to burnish it with a piece of ivory or smooth metal. The difficult part of correcting errors comes in putting back the ink lines . A line made upon an erased space is quite apt to spread and show larger than on the fresh paper, although the differ- ence is very slight, therefore the pen should be set for a slightly finer line, and this added to by successive strokes. If, in spite of all precautions, the place erased be treacher- ous, use two exceedingly fine lines as limits or walls, the distance apart of the thickness of the line to be drawn, and which, when dry, will prevent the filling ink from percolat- ing into the rough paper. In case of a very wide line, the retaining walls may have to be built up gradually. In repairing also it is necessary to overlap the correct part of the line sufficiently to include all that has been affected by the erasing. A very good hard drawing paper ought to permit several, say three or four, corrections over the same spot if skillfully managed. Corrections upon the rough side of tracing cloth are very easily made with the ink 54 NOTES ON PRACTICAL MECHANICAL DRAWING. eraser and no burnishing is necessary. On the smooth side, however, erasing is difiBcult and quite apt to irreparably injure the surface of the cloth. The greatest of care must be used by rubbing lightly to prevent trouble from this cause. A knife is almost sure to take off the surface, and if it does, burnishing will not repair the injury. A knife comes of service, now and then in one of two ways, first to scratch off the crust of large blots or very wide lines, without attempting to remove the ink entirely; second, to cut out an extremely small spot of ink or a slightly overlapping line. In the case of the latter, the knife should be run along the edge of the correct portion to cut it away sharply from the incorrect, then the error may be scratched free without leaving the correct Une ragged. 39. General directions for penciling drawings. The size of plates 12 inches by 18 inches, outside. Border line ^ inch from outside edge. Tach the paper by the upper left hand corner, then, with T sq. head against the left hand edge of board, swing paper into line with its upper edge. Next, drawing tight, tack upper right hand corner, then the lower two corners. If the drawing has to he temporarily removed, draw short horizontal lines on each side of the sheet and extend- ing onto the board, to guide in replacing. Hold the T sq. with the hand over the head or by the blade close to the head. With the latter way the blade can be made to creep by means of the fingers for short dis- tances across the paper. Keep the T sq. against the left Iniiid edge of the hoard, and use only the upper edge for working against. USE OF INSTRUMENTS. 55 Keep the triangles convenient to the T sq. and, when through using, move to the right or upward from the blade. In using a triangle against the T sq. observe the follow- ing method: Adjust the T sq. first with the right hand, bring the triangle into place and hold with the fingers of the left hand whUe the ball of the hand rests on the blade. FlGUBB No. SO. Rule all lines in pencil and ink in the directions shown In Fig. 30. The vertical lines should be ruled against the left hand edge of the triangle. Do not draw to the extreme point of the triangle. Lines locating points should cut each other as nearly as possible at right angles. Tlie lead pencil may he sharpened in one of two ways, by a long, tapering, round point or by a double-edged chisel. Cut the wood back for at least | of an inch from the end and leave from i to | of an inch of lead exposed. Taper both down continuously to, if possible, a slightly concave form. The advantage of a tapering point is that it holds its sharpness for a longer time, and again, the point is not thick enough to cover up the work in hand or to mislead as to where the lead is marking. 56 NOTES ON PRACTICAL MECHANICAL DRAWING. The double-edged chisel should not be quite as wide across as the lead is thick, but reduced somewhat, say to i the diameter. A penknife for the wood and emery paper or a file for the lead will give the desired results most rapidly. If the double-edged chisel is used it should only be for straight away lines, not for laying off measurements from the rule or scale. Hold the pencil nearly perpendicularly to the paper; if drawing lines with the round point, acquire the habit of slowly twirling the pencil during motion, so that the point will be worn down in a conical shape, and not irregularly. Clean, firm lines, uniform in thickness and blackness both in penciling and inking, are the kind which should be cultivated. Avoid drawing superfluous lines, lines overrunning their proper limits or lines that are not to be inked. If accidental errors are made, correct them with the eraser at once. Lines, which are to he dotted in final drawing, should be dotted in pencil so that no mistake is made when inking. After making an erasure, clean off the particles of dirt - that are loose on the paper, for they interfere with the smooth and proper action of the other tools. This is a particularly important direction to observe preparatory to inking and when any alterations are made during inking. To much care cannot be observed in freeing the paper and all tools from the dirt particles, for they are quite apt to get into the pen and give trouble. Successful work of any kind must proceed in a system- atic and orderly manner. A system in penciling cannot USE OF INSTRUMENTS. 57 be followed to advantage entirely, because the conditions in the development of a drawing vary quite a little, never- theless, a general plan can be followed when circumstances permit. The following is such a system:—* System in Penciling. 1. Draw border lines. 2. Draw match lines to guide in replacing the drawing, if it is temporarily removed. 3. Block out space for title. 4. Block out space for bill of materials. 5. Block out the views to be placed upon the sheet. 6. Draw main center lines, and where these are to be inked, they may be drawn full light lines. 7. Locate main lines of views. 8. Draw small and inside lines. 9. Put on dimensions and necessary notes. 40. General directions for inking. To put ink into a right line pen, hold the pen approxi- mately horizontal with the kind of holding usually given to a writing pen. Hold the bottle down with two fingers and with two fingers lift the cork out and touch the quill end between the nibs of the pen, to let the ink run in, and do this over the bottle, corking it securely when through. If the nibs of the pen get ink on the outside, wipe off with a rag. Hold the pen perpendicularly to the paper, steadying the hand against the ruling edge with the last finger or the last two fingers. Place the first finger just above the *Coolidge & Freeman, "Mechanical Drawing." 58 NOTES ON PRACTICAL MECHANICAL DRAWING. adjusting screw on the flat part of the nib, the thumb just opposite, and the second finger touching the pen between the first finger and the thumb and just below them to steady- it from any tendency to turn. Bear no weight on the pen, its own weight should be sufficient to make the desired line. If it does not, clean out and refill. Do not press pen against the ruling edge, as it will tend to close the nibs. Make all lines hy a continuous motion of the pen. Do not stop on a line to see where the rest of the line is to go. If it is absolutely necessary to stop in any case, even for a moment, lift the pen from the paper. Also, when stopping in this way, take the further precaution to move the ruling edge away from the wet line. When requiring refilling, clean the pen out thoroughly- inside and out. It is well to cultivate the habit of doing this early, making it invariable, for a pen clogged with ink is likely to give trouble. Use the nails of the thumb and first finger successively, covered by one thickness of rag, and' it will be found easy to clean one-half of a blade with one finger and the other half with the other, and the remaining blade by turning the pen over and repeating the operation. Four wipes generally clean sufficiently. If the pen gives any trouble in marking at any time it is safest to empty, clean and refill. The weight of an ink line on a drawing should be such that it will show clearly the form within the maze of dimension lines, etc., that it will blue print readily, giving an equally clear impression throughout, and that all annoy- ance is removed, due to the likelihood that the line will USE OF INSTRUMENTS. 59 FIQUEB No. 31. L/fT?/to fc 7 sac/y'o/? . tfif^*^^^ 1^JP3. Center///7e,. Out//r?&. 7^' 2s- break, through any obstructed flow from the pen. In Fig. 31 are shown suitable conventions to use on a drawing, as well as the proper weight of line. System in inking is more imperative than in penciling owing to the trouble of changing tools and waiting for ink to dry. A general plan which will be found useful follows : System in inking. 1. Ink all small circles and arcs of circles with the bow pen. 2. Ink larger circles and arcs with the compass. 3. Ink irregular curves with curve ruler. 4. Ink aU horizontal lines with the T sq. 5. Ink all vertical lines with the triangle resting on the T sq. edge. 6. Ink aU 45°, 30° and 60° lines in groups and in order. 7. Ink other oblique lines not at the above angles. 8. Section lining. 9. Dimensioning. 10. Surface tinting and shading. 11. Lettering and descriptive matter. 60 NOTES ON PRACTICAL MECHANICAL DRAWING. In large complicated drawings, treat a small portion of the sheet at a time complete with one tool until the whole has been covered. Some authorities advocate draw- ing center lines first, and it is also a good method. Section lining and dimensioning may conveniently change places in the series where dimensions do not have to be written across sectioned surfaces. 41. A drawing should be cleaned after all inking is finished. A soft rubber will clean o£E the dirt well, but it is not sufficient for erasing superfluous construction lines. Take the latter out carefully with a harder eraser so as not to injure the ink lines. 42. Handling of the compass, dividers and bows. The compass is for describing circles and measuring angles, and also for transferring measurements from one place to another. The dividers are used to approximately subdivide linear distances and for transferring measurements from one place to another. It is, many times, a more conven- ient tool for doing these things, and one of the habits to cultivate is to minimize the use of the dividers. It is an excellent tool in its place, but it is not as safe to depend upon as the scale. In changing the marking legs of the compass, use care to pull or push the attachment longitudinally of the leg, and not to twist it or move it laterally, it might strain the members. The instrument is easily injured, and accuracy of action is necessary. The needle point of the compass should have a shoulder USB OF INSTRUMENTS. 61 on it to prevent sticking too deep in the paper; it should be adjusted to fit the pen attachment and always be kept so. In working with the pencil leg_ then, and as it wears down, extend the lead to meet properly the needle point adjustment. The pencil in the compass should be sharp- ened always to the double-edged chisel. The proper position for the needle point is slightly in advance of the marking point, depending upon the degree of sharpness and the length of the point. At no time should the point more than hold in the paper. And when stuck in to this degree, the bisector of the angle of the com- pass legs should be perpendicular to the line connecting the two points. This is very important in making small circles. The compass should he held with one hand only, for reasons apparent after experience. To open the compass at first, press the thumb and first finger against the bevelled portion near the head. To hold the compass when opened, control the needle point leg with the thumb and third finger, the marking leg with the first and second fingers, held generally, the former upon the outside, the latter upon the inside of the leg, so as to move the leg in and out with a controlled motion. The tightness of the head should be just sufficient to hold the compass in place during use ; such an adjustment will not render it difficult to change the angle between the legs easily with the fingers as described. If the hand is unsteady, it may be found convenient to use one hand for putting the needle point in the proper center, either by taking hold of the end of the needle point leg or by resting the leg against the finger while putting it into place ; the latter is the better way. 62 NOTES ON PRACTICAL MECHANICAL DRAWING. Curves should be drawn continuously and always clock- wise. In drawing a complete circle, start the marking point at tlie lowest part of the circle, or even a little to the right, and it will be found possible to swing the whole circle without change of handling, by rolling the head in the fingers during rotation. It should not be necessary to change the handling at any time, or the position of the hand on the instrument. Held correctly, it should always be ready for drawing. It is a very common fault to hold the compass with two hands. It should be held so that the head is slightly in advance of the marking point in the direction in which the curve is being made, to aid the marking point to remain in contact with the paper. But do not bear any more pressure on either leg than is necessary to make the curve and to keep the needle point in contact with the paper; in ink work, the weight of the instrument, as in the case of the ruling pen, should be sufficient to make the desired line. Do not overlap a circle in inking; there is a chance of a change of adjustment, and even if this is not the case, it is likely that a line twice drawn over wUl spread out making a noticeable junction. The hairspring attachment put on some compasses and dividers has merits in enabling one to make a very delicate change of adjustment, but the author thinks the value of this feature is very much over estimated, for, with experience, comes sufficient skill that, handled as above described, the desired adjustments are made more rapidly than they could be by a hairspring attachment. Of the two instruments, however, the hairspring is of more value upon the compass than upon the dividers. USE OF INSTRUMENTS. 63 For large circles, bend the legs of the compass at the joint provided so that they come down perpendicularly to the paper. A lengthening bar is used for circles beyond the capacity, ordinarily, of the compass, but it is an inconven- ient thing, makes an unsteady tool, and if much work is to be done on large radii it is well to use a beam compass, built especially for this purpose. The dividers are held in the same manner as the compass. If a given distance is to be divided into a certain number of equal parts that do not correspond to any scale divisions, the dividers can be used to do it by successive approximations. In stepping ofE such equal spaces, the tool should be swung alternately over and under. More- over^ but slight pressure should be exerted on the tool, so that the points make no noticeable hole in the paper. To locate a pick of the divider leg for further reference, put a small free-hand circle about the point, not much over a sixteenth of an inch in diameter; this calls attention to the region in which the point lies. Large holes in a draw- ing are unsightly and are really inaccurate. The how instruments are very convenient, small and accurate tools for doing the same kind of things that the compass and dividers will do. The adjustment of needle to marking point in the bow pen and pencil should be even more carefully made than in the compass, because of the small circles for which they are used. On account of their accuracy and positive adjustment, the bows in practical work are used wherever they can be, but since there is nothing distinctive to be learned about them, the beginner is advised rather to favor the use of the latter so that he 64 NOTES ON PRACTICAL MECHANICAL DRAWING. may get as much practice with them as possible, and acquire the proper handling, which does not generally come naturally at first. The small circles upon commercial drawings are not infrequently omitted in penciling, only the centers being located, but a caution is extended to the beginner not to resort to this form of short cut, but to pencil in everything very completely and accurately. The omissions of con- struction should be left to the judgment of the skUlful draftsman. If a decided change is to be made in the adjustment of the hows, it is less wear on the instrument and also more economical of time to take the strain o£E the legs by press- ing them together with one hand while the thumb screw is twirled around with the other untU near the proper adjustment. 43, The use of the irregular curve: The irregular curves are those which cannot be drawn accurately with the com- pass. They must be plotted by points and the latter joined by a smooth curve made with the curved ruler or "curve" as it is called. The curve can be drawn best at first free-hand and then copied with the "curve." The correct shape for a "curve" is of importance. The best is one which has the fewest and simplest curves in one tool, as the spiral form for example. The "curve" should be applied to the points plotted with the direction of the change of curvature the same in both. The drawn curve should he as unhroken as the theoret- USE OF INSTRUMENTS. 65 ical curve, and its execution is not easy at first. To insure matching the curve, apply the "curve" to at least three points, more if possible, then draw, not as far as the ruler seems to match the curve but a little short of it, the amount depending upon how rapidly the ruler departs from the curve to be drawn at the last discernable point. Again, in moving to the next segment, match the ruler to the part already drawn so that it corresponds with it for an appreciable distance back of the last point drawn to. To connect the segments of the line accurately, head the pen first to make a perfect alignment, then start to move on the line, or if drawing up to a line, and just before reaching it, tilt the pen, if necessary, to bring it into the ink line correctly, but do not overlap. Keep the blades of the pen at all times tangent to the ruling edge, but do not work on the under side of the CHAPTER V. WORKING DRAWINGS. 44. Orthographic projection and working drawing. Orthographic projection is the language in which working drawings are written, but a dimensioned orthograghic projection of anything does not necessarily constitute a working drawing of that thing. A working drawing must be simple and plain in its fea- tures, easy to be interpreted, yet explicit. For if one view of a piece will suflBce to tell a workman how to make it, only the one view need be made. On the other hand, however, more views may be required in the working drawing than are required in orthographic projection, for sometimes assembly views are needed to show relation of all parts and detail drawings of each component part in addition. The principles of orthographic projection are frequently violated in working drawings wherever modifi- cation will aid in legibility or economy of time in drawing. There is no way to formulate this difference between the two under rules for there are no fixed ones. The draftsman should place himself in the position, in imagina- tion, of the one who is going to construct from his drawings, and in that way arrive at a conclusion as to what would be desirable in the way of views. Unless the draftsman does this, he is apt to economize time and effort at the expense of the workman's time. From the workman's standpoint, many times, drawings are not explanatory WORKING DBAWINGB. 67 enough; he will want them too elaborated with directions. A mean of these two has to be struck. 45, A set of working drawings in its completest form, consists of diagrams, assembly views, details, sections and bill of materials. A diagram is a drawing which is first made to deter- mine upon the arrangement or lay out of the various parts. Upon this lay out, also, may depend the character of the forms, so that this is an additional requirement for its being made first. The diagram shows, further, the number of the various elements of the group. As one illustration of this kind of drawing can be mentioned a layout for piping, , showing the number of elbows, tees, valves, etc. In a diagram the briefest indication of shape is given, and not infrequently special conventional forms are used to stand for the more intricate actual forms. In piping, for instance, a valve is represented by two short lines perpendicular to and crossed by each other, one per- pendicular to the line of piping and standing for the entire valve, the other parallel to the line of the piping and standing for the handle. Another illustration of the diagram is an outline of a machine composed of the main lines, together with the usual center lines. Perhaps, in this, the relation of some of the moving parts is shown. These may be represented by heavy lines coinciding with the center lines of the members for which they stand, as in a Corliss engine valve gear diagram. The assembly drawing shows the entire subject to be 68 NOTES ON PRACTICAL MECHANICAL DRAWING. treated. It may not show all the features, or parts, only the principal ones; but it gives certain facts not available in any other way. It shows the size of the whole, the place for the different coroponent parts, and the relation between these, together with certain desirable chief dimen- sions. The minor features, such as bolts, nuts, keys, set screws, etc., are left off. Perhaps their place will be indi- cated by center lines; perhaps, not even that. In fact, the assembly drawing may be more or less in the form of a diagram. The details are made together upon a sheet of details, or each may be made on a separate sheet for the different workmen, according to the process through which the parts are to be put. There are details, for example, for the pattern maker, the blacksmith or the machinist. The dimensions put on these and the general treatment will be that of interest to the particular workman handling them. Sometimes the detail drawings are made complete enough in all respects to answer for the several above mentioned requirements. 46. Sections are made many times to save the drawing of details. A section in its simplest form, means to cut anything as with a saw and to show by some conventional, or commonly understood means, the plane of the cut and what lies beyond this plane when looking perpendicularly at it. The treatment of sections will be taken up a little later. 47. The bill of materials is a tabulation of the stock required, the number and character of the pieces needed. WORKING DBAWINGB. 69 To be specific, it is composed of: (a.) An identification mark as a number, which may, by its denomination, indi- cate the material. (&.) Name of the part, (c.) Number of the pieces needed to make one of the entire subject. (d. ) Name of material, if the identification is not complete as above, (e.) Further general descriptive matter, like pattern number, dimensions of the rough stock, method of casting, eitc. In very small subjects it may not be made a separate tabulation, but written near the separate parts. In other cases it may be a tabulation in one corner of the sheet containing the pieces detailed. When very com- plicated drawings are dealt with, it may be accorded a separate sheet or sheets. 48. Working drawings may violate the rules of ortho- graphic projection:— Projection is the theoretical side, working drawings are the practical application of theory. Custom has santioned certain practices, more or less universal, for making drawings more explanatory with less labor, while there are innumerable short cuts, etc., adopted by different establishments, known only to the individuals having use for them. Some few of the general principles which may be followed will be here touched upon : * (a.) "That in each separate view, whatever is shown at all should be represented in the most explanatory manner." (6.) "That which is not explanatory in any one view may be omitted therefrom, if sufficiently defined in other *McCord Meoh. Draw. Part II, Page 8. 70 NOTES ON PRACTICAL MECHANICAL DRAWING. (c.) "The proper position of a cutting plane is that by which the most information can be clearly given." id.) "It is not necessary to show in section every- thing which might be divided by a cutting plane." (e.) "Whatever lies beyond a cutting plane may be omitted when no necessary information would be conveyed by its representation." The views necessary to show a subject do not follow the conventional ones of projection, for if one view is sufficient to tell the workman all the facts, more are super- fluous; for example, one view of a bolt is all that is needed when the bolt is standard. The certainty that the work- man could not make anything else from the drawings than the thing intended is the controlling condition. When two pieces differ only in being rights and lefts, it is usually not necessary to draw but one of them, making an explanatory note on the drawing that two are wanted, one right and one left. A section and an elevation are sometimes combined on the one view by superimposing the lines of the elevation over those of the section. This saves one view. Lines coming very close when drawn to scale should be separated, that is, the scale exaggerated, or else one line left out. In gears, a few teeth, perhaps only one, are drawn out in full ; the remainder are indicated by dotted circles for their crowns and for their roots, the pitch circle being a dash and dot line, or the usual convention for center line, or it may even be made a solid line. In sectioned views, continuity of material is not inter- WORKING DRAWINGS. 71 fered with by the introduction of minor elements in the plane of the section. They are either left out or put in dotted. Sometimes in the drawing of one part of an object, which it is particularly desired to show, there are other parts connected with it which may be rendered in dotted lines to help show the connection of them all. And so illustrations may be multiplied, but it is not necessary to go farther. The different illustrations in the book will show some of the short cuts. Judgment and experience will open up others to the thoughtful drafts- man, and he will even then occasionally find that there are opportunities for him to improve on past experience. 49. The development and arrangement of working drawings. In beginning a set of working drawings of a subject which is entirely new in design, it is possible that the small features will be designed first, and the assembly drawings of parts, or of the whole, made afterwards, so there can be no rule for the order in which drawings are made. Differences in manufacture and in the subject control the method of development and arrangement. Principles cannot be laid down applicable to all cases. Some one problem may be considered somewhat in detail, and will serve to show how it is done, and about the best illustration that can be taken is an academic exercise, a problem which would be given a student in drawing, that of making a set of working drawings of a model of a simple steam engine. Determine the chief dimensions or size of the whole, 72 NOTES ON PRACTICAL MECHANICAL DRAWING. and choose such a scale which will properly present the assembly drawings, a plan, elevation and end view, upon one sheet without overcrowding the sheet. Next, take in turn the various parts, and make the necessary working drawings of each. It is best to take a survey of the size of the largest piece and of the smallest, and see of what size they can be conveniently made, using only one scale for all. Lay out the projections of the larger pieces first, and proceed toward the smaller, and so on. Details of construction: Before any drawing is done, a list should be made of all the features needing to be detailed, and the number and kind of views required of each, a written list is preferable. The arrangement of the sheets should next be decided upon. In practical, work different sized sheets are used for the different parts of the subject; frequently, the assembly views will be made upon a relatively large sized sheet, the main details on a second or medium sized sheet, and the smallest parts on small sheets. Small parts require, generally, finishing or machine work, and it is more con- venient in the shop to handle the small sheets, mounted as they often are, on board, or some stiff backing, and var- nished. To get the best arrangement, a free hand sketch treat- ment should be used first, that is, to an approximate scale, sketch roughly, by very light lines, the space to be occu- pied by each and all of the views. This will permit of an adjustment in the arrangement, if it does not at first promise to be good. Begin the careful drawing of the details first, leaving the assembly drawings until later, as the best interpreta- WORKING DRAWINGS. 7S tion and accuracy can be reached in working the assembly from the details. Draw the views of the bed of the engine first. Do not begin at the top or bottom, and build steadily down or up until finished, but lay out the chief, or the over all sizes, then the next smaller, and so on, to the smallest parts last; also, drawing not one view at a time, but the several of the set ; the same features recurring in the several views should be treated in them all, so that there should be harmony of parts. If a view can be developed by projection from another, it is better to do so than to use the scale and lay it out independently, for it saves time. But the scale relation must be kept in mind and discrepancies noted. The place on the sheet for the different views should be appropriate and follow a certain system. Large details should be put on a sheet by themselves, or else along the upper part of the sheet, or at the left hand side. The next smaller parts should be put below the first, or to the right, and so on, so that the smallest parts are shown along the bottom, or along the right hand edge of the sheet. Related parts may be in protectively , related positions, provided the subject admits of it, or whUe not in project- ively, related positions, they may be so intimately related on the drawing that the connection is apparent at a glance. For illustration: A connecting rod— showing the rod at the top— may have the straps to the left and right of the rod as if they had just been slipped off, their center lines coinciding with that of the rod ; the brasses may be shown also to the right and left of the straps as if they had been. 74 NOTES ON PRAOTICAL MECHANICAL DRAWING. removed by simply sliding along their center lines coin- ciding with that of their position in the straps ; finally, the keys, and bolts, etc., may be put in the lower part of the sheet in any convenient place, arranged so that the left hand bolts, etc., belong at the left hand end of the rod, and those at the right, to the right hand end of the rod. This may be seen illustrated in diagram. Fig. 32. Another logical and perhaps better arrangement is shown in diagram, in Fig. 33. Here the principle is fol- lowed of placing parts of a kind together, disregarding their exact position in the subject. The straps of both ends are put together at the left, but the upper one belongs to the left hand end of the rod, and the lower one to the right hand end of the rod, a certain convention of sequence which is quite common. Similarly, the brasses are placed at the right with, again, the left hand brass above and the right hand one below. The last mentioned plan of Fig. 33 is the best in general. If the engine were complex, probably the connecting rods would be put on a sheet with the eccentric rods, or other long turned members, the brasses all together on a sheet by themselves, and the straps also. Even here, however, the rods for the high pressure (H.P.), low pressure (L.P.), and intermediate pressure (I.P.), would follow each other down or across the sheet in a certain sequence, which would be the same as that on the sheet of brasses and straps, etc. It is evident that such an arrange- ment would aid materially in reading the drawings and finding what is wanted. If several parts of the engine are put on a sheet, the groups of drawings of them should be separated by a little WORKING DBAWINGa 75 XJ m 76 NOTES ON PRACTICAL MECHANICAL DRAWING. o ^ ] TI Jl TI II ^ ^ } e t) h WORKING DRAWINGS. 77 more space than the several views of a part, so that the identity of the different things is not confused. Parts which have to be made upon the same machine, or by similar processes, are often collected on a separate sheet by themselves ; for example, there may be a sheet of bolts alone, of screws, of forgings and of castings; but this is done only where a large number of parts is wanted, and where, moreover, processes of manufacture have become somewhat systematized. If it takes more than one sheet to make a set of drawings, keep each sheet as far as possible self contained, even though on some sheets there may be waste room. The economy of space profits little, nor the even distri- bution of views over the sheet unless it can be done with- out any sacrifice. 50, Drawing to scale is necessary where forms dealt with are larger than the ordinary sized drawing paper will take full size. It is no hindrance to the workman, because he takes his sizes from those specified on the drawing and is generally not permitted to use anjiihing else. There are a number of kinds of scales made, divided broadly into civil engineer's and architect's or mechanical engineer's and are either flat or triangular. The civil engineers^ scale is one in which the divisions of inches are by even decimals, tenths, twentieths, thirtieths, etc. The flat scale may contain two, four or eight scales, according to the way in which its edges are divided, and is a conven- ient tool because of its flatness. The triangular scale usually contains twelve different scales, and because of its wide range is probably the favorite. 78 NOTES ON PKACTICAL. MECHANICAL DRAWING. In engineering, when scale is mentioned, it means so many inches or fractions of an inch will stand for a foot of the actual thing drawn. To take a concrete case: On one face of the triangular scale, the edge is divided into 3-inch major divisions, identified by numbers on the flat surface, the edge is also divided into 1^ inch minor divis- ions, identified by numbers on the curved part of the scale. At the right a three inch space is divided into twelve major divisions to stand for inches and each of these again into eighths. At the left a H inch space is similarly divided, except that each space standing for one inch is divided into quarters. Hence, by overlapping, we have two scales to an edge. To lay off a dimension with the three inch scale we read the even feet to the left of the zero mark and the inches or fractions to the right. Points to he observed in the handling of the scale: — It should never be used as a rule. With a sharp and round pointed pencil, make a short straight stroke at the scale division, and perpendicular to the edge, about one thirty-second of an inch long. Transfer measurements with the scale where possible, that is, indicate the size by scale measurement, then set the compass to the marks made if it is necessary to strike an arc of that radius. Successive measurements should be laid off with one setting of the scale where possible. The problems arising in the use of the architect's or mechanical engineer's scale group themselves under three heads. WORKING DRAWINGS. 79' (1.) To make a drawing a given fraction of the original in size. (2.) Given the scale used to determine the fraction of size which the drawing is of the original. (3.) Given the size of the space in which a drawing must be made to fit, to determine the scale to be used to get this reduction from the original. (1.) To illustrate : Suppose it is desired to make a drawing one-quarter the size of the original; ixl2 = 3; therefore 3 inches is the scale or size per foot to be used. (2.) To illustrate: Suppose a drawing is made to a scale of one-quarter of an inch to the foot, then, as i : 12 so the drawing is to the origuial or -jV the size. (3.) To illustrate: Suppose a subject 3 feet long is to be reduced in drawing to 1^ inches, the length being the determining dimensions, then 1^ : 36x12 = i, or the scale is i inch to the foot. When problems do not come out as even as these, the nearest available scale is taken.* There is a special and popular form of scale made for mechanical engineering work which differs in divisions from the ordinary scale. The inch and not the foot is made the unit for subdivisions. The scales shown are for half size, quarter size and eighth size. The half size, for example, has a half inch divided again into halves. *A very common error arises from mixing up scale with traction. A quarter scale drawing means a drawing made i Inch to one foot, while a i size drawing means a drawing made 8 Inches to a loot. In other words when we speak ol a fractional size we do not mean that fraction as the scale but that fraction of 12 Inches, the foot being the unit. 80 NOTES ON PRACTICAL MECHANICAL DRAWING. quarters and eighths, to represent those fractions respec- tively of an inch. Sometimes a purely arbitrary and exact scale is required, and has to be constructed. It can be readily done by a method based upon the geometrical principle that lines parallel to one side of a triangle divide the adjacent sides in proportional parts. The civil engineer's or decimated scale is mainly a scale for use when the reduction is relatively large so that from 10 to 100 feet will be represented by an inch, for it has divisions of lOths, 20ths, SOths, 40ths and 50ths of an inch. It can also be used in the same way as the mechanical engineer's scale. To illustrate: The twentieths scale can be used for i inch to the foot, five divisions being equivalent to one foot, two and one-half to six inches, etc. The thirtieths can be used for six inches to the foot, five