TURNING AND BORING TAPERS BY FRED H. COLVIN BEING NUMBER^ ^ ' ; OF A SERIES OF PRACTICAL PAPERS PUBLISHED BY NEW YORK '\ ^*^ LIBRARY of CONGRESS Two Copies Received DEC 24 1903 Copyright Entry H Turning and Boring Tapers The problem of turning tapers — or more properly the taper wanted — is often puzzling, and ''rules" are frequently asked for. 'As is often the case, a clear understanding of the question is much better than a rule, for this might easily be applied in the wrong way. Tapers are designated either by the amount per inch or per foot or the number of degrees of the angle made by the sides and the center line or between the sides. This latter sometimes causes confusion, as will be seen later, but each method will be carefully ex- plained. Derry CoUard Co I Figure i. Showing taper at various points. When they are designated by the amount per foot, the usual way, the difference in diameters is always meant as in pipe thread tapers or in taper ke3^s. Thus, pipe threads taper % of an inch to every foot in length or I inch in i6 inches. This means a pipe tap with this taper and one foot long would be 3^ of an inch larger at one end than the other or that the diameter would increase -^^ of an inch to every inch in length, as shown in figure i. Copyright 1902 by The Derry-Collard Co, Turning and Boring Tapers. To avoid confusion, the drawings or instructions should say plainly whether the angle mentioned is between the center line of the bar or between the sides, the former being just half the latter, as seen in figures 2 and 3. In thinking of the angles it is simpler to think of the sides (or the total or. included angle), as the center line is an imaginary affair at best, but when using a Figure 2. Angles each side of center line. compound rest on a lathe we run against the center line unless we are careful. This will be shown in the section under compound rests. Turning tapers between centers being the method usually inquired about, will be first considered. In all the views shown we are looking down on the lathe. Derry CoUard Co Figure 3. Total angle. With both the live spindle and the tail stock or dead spindle in line and centers true, a piece of work will be straight or of equal diameter at both ends — a condition unfortunately that is not as easy to obtain as might be imagined. Turning and Boring Tapers. Remembering that the lathe tool moves with the carriage in a line parallel with the lathe centers when they are in line, it is easy to see how any variation in the position of either center will make the lathe turn smaller at one end or the other. The end on the center nearest the tool will of course be smaller than the other, as indicated by figures 4 and 5. Derry CoUurd Co Figure 4. Ordinary method of turning tapers. With very few exceptions, tapers are turned with the small end toward the dead center or tail stock, so that the dead center is always moved toward the tool or front of the lathe. Should it be necessary to turn a taper like figure 5, the dead center must be moved back as shown. Tapers of the regular kind will be consid- ered, however, in every case, and any movement of the Derry CollarJ Co Figure 5. Large end at tail stock. tail Stock from the center line will be toward the front. It may be well to mention here the effect on the work if the centers are out of line vertically — that is, 3 Turning and Boring Tapers. in line back and front, but the live spindle higher or lower than the tail stock. With the dead center either higher or lower than the live center the taper will be less than if they were in line. This difference in diameter will not be nearly so great as though the centers were out of line the same amount sideways or horizontally, but it must be guarded against when on especially nice work. 1/2 to 4 — 11/2 to 1 foot Derry CoUard Co Figure 6. Taper given a 4-inch piece. Suppose we have a piece of metal 4 inches long and 2 inches in diameter, and can hold this by simply touch- ing the centers against the ends, as shown in figures 4, 5 and 6. If we wdsh to make this taper so as to be i^ inches at the small end and still be 2 inches at the large end, we move the tail stock over ^ of an inch or half the difference between the diameters of the two ends of the taper. This is shown in figure 6, and we would then have a taper of Y-z an inch in 4 inches, i inch in 8 inches, or i Y-z inches to the foot, which is the usual way of expressing it. Now, suppose we put in a piece 8 inches long in- stead of 4 inches. The tail stock is set over Y\ inch so that the small end must still be Y'^ an inch smaller in dia- meter than the large end, leaving it i Y'^ inches as before. Turning and Boring Tapers. But the taper is now ^ inch in 8 inches or 3^ inch to the foot, only one-half as great as before. This is shown in figure 7, and shows very plainly that the taper cut by the lathe depends on the length of the piece and amount of offset given the tail stock. To a slight extent it also depends on the hight of the cutting point of lathe tool, which should be at the center. If this cutting point is either above or below the center the taper will be slightly less, as the cutting point is then a trifle farther from the dead center. This does not affect it to any great extent, however, but should be noted. Continuing on the basis that the centers bear against the ends of the piece to be turned, which is not practical, but makes it easier to calculate, we come to the problem of finding how much to set the tail stock over to turn a given taper on a piece of a certain length. In practice the tapers turned are usually on the end of a bar, and it should be remembered that the Vz to 8 - /^ to 1 foot Pipe tap taper Derry Collard Co Figure 7. Taper on 8-inch piece — same offset. length of the taper is of no consequence, as far as set- ting the lathe is concerned, but only the amount of taper and the length of piece to be turned. If you want a taper portion 3 inches long on the end of a bar that is 18 inches in length, and the taper is to be i inch Turning and Boring Tapers. to the foot, the tail stock must be set over one-half the amount of taper per foot for every foot of length of the bar. As the bar is i^ feet long, the tail stock must come over i Y-z times ^ inch, or 3^ of an inch. We can either reduce the taper to the amount per inch and then multiply this by ^ the length of the bar in inches, or find the taper for the entire length and then move the tail stock over one-half of this. The latter is the easiest, as we shall see from the following example: Bar is 39 inches long, 2 inches in diameter. Taper of ^ inch to foot wanted at one end, and the small end must be 1 3^ inches when finished. How far must tail stock be set over and how long will taper be? One-half inch to foot is -gV of an inch to each inch in length, and 39 inches times -^ or -||- or ijf or i^ inches in the length of bar. Then tail stock must be set over one-half of i^. As i^ equals -g-, one-half of this is yf of an inch. Or we can call 39 inches 3%' feet, and we find that total taper is 3^ times'^, or i^ inches as before. As the taper is }^ inch to foot and the small end must be I % inches, or y^ inch less than the original, it is evident that the taper will be 6 inches long, as the reduction in diameter is just half the taper per foot. Another way of determining the offset for the tail stock when there is a taper to be turned on the end of a long piece is as follows : Suppose the bar is two feet long and you want a taper 6 inches long. The large end of taper is 3 inches and the small end 2 inches. Divide the difference between the large and small ends by 2, that is, 3 minus 2=1 and divided by 2 gives Yz. If the taper was the whole length of bar this would be the offset. Turning and Boring Tapers. As it extends only one-quarter the length of the bar, the offset will be 4 times ^ inch, or 2 inches. This makes the rule as follows : " Subtract small diameter of taper from large end and divide this by two. Multiply this by the length of the bar and divide by length of taper. Or, divide length of bar by length of taper (both in inches) and multiply the offset first found by this amount." Those who like formulas might prefer this : — /.= length of bar. / = " " taper. Z)=:large diameter of taper. ^=small " L D — d Then the offset equals -^ X — ;; — , or in this case 24 3 — 2 -— X — - — = 2 inches offset, u 2 / Figure 8. Action of work on centers. Having seen how tapers are made under the imag- inary conditions named, we must now consider the prac- tical questions involved, the most serious being the fact that the centers must enter a sufficient distance to sup- Turning and Boring Tapers. port the work, and that the work is carried in a cramped and constantly changing position owing to the offset, as shown in figure 8. It will be seen that the effective length of the bar, so far as our calculation is concerned, has been short- ened by the depth of the center on each end, and the depth of both must be deducted if we wish to get down as fine as possible. The longer the piece or bar, the less each center is li inch Derry Uollard Co Figure 9. Taper bearing at ends only. deep, the effective length of bar is only reduced from 24 to 23)4 inches — a change of nearly y|„- of an inch to the foot ; and the careful man will want to know why the taper is not exactly as calculated. As a matter of fact, it is not wise to depend too much on calculations in this case, as at best they are only a guide, and the practical man measures very care- fully with a gage, if he has one, or with calipers at two points a measured distance apart. The calculations are useful in getting pretty near the right taper, but it is safer to measure after each cut and adjust the tail stock accordingly. In fact, turning a taper just right or two just alike in an ordinary lathe is not always easy to do. Turning and Boring Tapers. Where it is not necessary to have a fit the whole length of the taper it is a rather common practice to relieve the taper in the center of either piece, as it is much easier to obtain a g^ood fit, free from shake, than when taper extends the whole length. This is shown in figure 9. In the foregoing, tapers have been considered as a given amount to the foot, as is usually the case when turned by moving tail stock. When tapers are desig- nated in degrees, the angle is usually obtained by the compound rest, but for the convenience of those who v/ish to compare the two, the following table has been prepared : Equivalent Tapers of Degrees in Inches. Total number of degrees Total taper per inch in Total taper per foot in included in angle. inches. inches. 1 .01746 .20952 2 .03490 .41880 3 .05236 .62832 4 .07984 .95808 5 .08732 1.04784 7% .13108 1.57296 10 .17498 2.09976 15 .28330 3.15960 20 .35266 4 23192 25 .44338 5.32056 30 .53590 6.43080 35 .63060 7.56720 40 .72794 8.73538 45 .82842 9.94104 50 .93262 11.19144 55 1.04114 12.49368 60 1.15470 13.85640 Tapers with Compound Rest. The compound rest is an attachment between the lathe carriage and the tool post, capable of being swung around to any angle and having an independent feed screw so that the tool can be fed by this independent screw at the angle desired. The base of the compound rest is indexed or divided into degrees so as to be con- TO. ** Squaring off" with compound rest. Derry Collard Co veniently set. This makes it very easy to set the rest so as to cut the desired angle after you know what it is, but as there is often confusion on this score it is best to set it straight before we commence. With the centers in line as for straight turning, compound rest "square" or at right angle to the "shears" or 'Svays" of the lathe, it will face off a piece so that the end will be 90 degrees from either the out- side or an imaginary line running between centers, but the "included angle," or the angle from one side of the 10 Turning and Boring Tapers. part just cut to the other, as shown in figure lo, will be twice 90, or 180 degrees. Compound rests are differently arranged by the various makers, and the manner of graduating them might tend to confuse if we do not thoroughly under- stand in the beginning. In some the graduations are on the back, some on the front, but they are mostly on the side. A very common way — and a good one — is to gradu- ate each w^ay from a center line, and as 90 degrees or quarter of a circle is generally used, this gives 45 de- grees on each side. With a mark on the lower or stationary part at each end of the divisions, it is easy to turn to any desired angle with the lathe centers. This is shown in figure 11. Derry CoUard Co Figure 1 1 . A common method of graduation. If the graduation is as indicated in figure 12, you can only measure 45 degrees in either direction or 90 degrees in all. By increasing this to 60 degrees and putting additional marks at 30 degrees each side of these, 180 degrees can be obtained as with the first II Turning and Boring i apers. g-raduation shown. But in any case, if you remember that it is the number of degrees ''out of center" or away from normal position that counts, there will be no trouble. Now, if we move the compound rest out of center 15 degrees, as shown in figure 13, we shall make a cut which is 15 degrees away from the square facing-off movement of carriage, 75 degrees from the center line and 150 degrees of included angle, as shown. This is what fools many a man who is not used to angles or a compound rest, for having moved the rest 1 5 degrees, he never thinks but that he will get a 1 5 degree angle. Deny CoUai il Co Figure 12. Another method He will if he measures from across the end, but in no other way. This shows the necessity for having draw- ings plainly marked, so as to show whether the angle given is the total or included angle or the angle be- tween the center line and the side. The total or in- cluded angle is the one generally meant, and will be considered. 12 Turning and Boring Tapers. There is too little care used in expressing angles of globe and other valve seats. A 60 degree seat is common and means 60 degrees total angle, as it should, but in the next breath we speak of a "45 degree seat," when it should be a "90 degree seat " instead. Setting the compound rest to 30 degrees and we have a total angle of 120 degrees, while if it goes to 45 degrees, it gives a total angle of 90 degrees. Figure 13. Compound rest moved 1 5 degrees out of center Derry CoUard Co From this we can make a little rule to the effect that " the total angle of the piece turned will equal i8o degrees, minus twice the setting of the compound rest from the square position," or "subtract the desired total angle from i8o degrees and ^ of the remainder is the correct setting of the compound rest." We wish to turn a valve seat reamer to 60 degrees total angle, what is the correct setting of the compound rest? Then 180 — 60=120, y^ of 120=60, which is the correct number of degrees out of center, for setting the compound rest? Turning and Boring Tapers. A reamer is desired, having a total angle of 15 degrees, what is correct setting of compound rest? Then 180 — 15=165, y^ of i65=:82%, or within 7>4 degrees of being parallel with the lathe centers. A little thought wdll show this without the rule, as by taking half the degrees in the total angle desired from the right angle position of the com_potind rest you get the correct angle. With the compound rest set 50 out of centre, what will be the total angle cut? Twice 50=100, 180 — 100=80. Total angle cut will be 80. In all compound rest turning or boring, as w^ell as with taper w^ork of any kind, have cutting point of tool at hight of lathe center. ▼ ▼ V Taper Turning Attachments, Several makes of lathes have taper turning attach- ments to avoid the setting over of tail stock and its attendant evils. They are all based on the idea shown in figure 14, although this is a rather crude application of the principle. The tool block is disconnected from the screw and fastened by piece B to a block sliding in or on the piece A A, which is moved to any desired taper. One end of this is moved the same amount as the tail stock would be, or if both ends are moved, the total movement out of central position in opposite directions must equal half the amount of taper in a piece as long as the piece A A. This supposes the graduations to be at the end of the bar A A. If they are not, the length should be taken at the graduating point. The 14 Turning and Boring Tapers, length of the piece being turned does not count here, but the length of the piece A A or that part of it which controls the movement of the tool block. Derry Collard Co Figure 14. Principle used in taper attachments. If the taper bar or piece is 12 inches long, and we wish to turn a pipe taper which is ^ inch per foot, then it must be set out of center one-half this amount or ys of an inch. Others tapers are found in the same manner, and if the taper is given in degrees, the equivalent taper per inch and per foot can be found from the table on page 9. T T T Taper Boring. Taper boring differs from taper turning, as it can- not be done by setting over lathe centers unless a boring bar is employed, or as shown in figure 16. This is only one type of bar, but the idea is the same in all. The bar is held stationary between centers which are Turning and Boring Tapers. set over the correct amount. The boring tool is held in a cutter head, which is moved along the bar by the screw S. This screw is turned either by hand or by a lug fastened on the work, striking a star wheel on the screw every revolution and giving the screw a partial turn. With this, the tail stock is set over just as though the boring bar was the piece to be turned, as in our first problem except that the tail stock is m^oved forward instead of back. The exception to the first statement made in regard to boring tapers is in a case similar to that of figure 1 6, which shows a friction pulley being bored in this Derry CoUard Co Figure 15. Boring tapers with boring bar. way. Where the diameter of the work is large in pro- portion to length to be bored and it can be driven on an arbor or centerpiece of the work itself, this can be done. But in these cases, which are rare, the tail stock must be set forward, as shown in figure 5. Where work is bolted to face plate or held in a chuck, as is usually the case, the taper must be obtained with a compound rest or some of the taper attachments. The latter are the best in any case, as setting over the tail stock and running work at an angle on centers is a barbarous proceeding at best. 16 Turning and Boring Tapers. Turning tapers on brass working lathes is usually accomplished by the slide rest, which can be compared to the compound rest of the engine lathe, or by using v:r^ Uerry Collard Jo Figure i6. Boring taper work held on arbor. a tool in the tail stock spindle and swinging the tail stock around the desired amount. In this latter case^ the work is held in screw or other chucks. T ▼ ▼ Taper Threads. The cutting of threads on tapers is sometimes the subject of much discussion. Some contend that the thread tool should be at right angles to the taper sur- face, but it is generally conceded that it is better to make the thread at right angles to the center line of the taper piece. The difference in the two methods can be seen by comparing figures 17 and 18. The taper is here very sharp to show the difference more clearly. The thread tool can be easily set by taking the taper work out of the centers and putting in a straight 17 Turning and Boring Tapers. Figure 17. Thread tool square with lathe. piece of work, such as an arbor or mandrel. Then use this to square the tool point by the thread gage and you Figure 18. Thread tool square with center line of taper. la Turning and Boring Tapers. have it with almost no trouble, and all guesswork is avoided. In this connection it may not be amiss to offer a suggestion regarding taper fittings for pipes. Standard pipe fittings are yq to the inch or 3^ inch to foot, and for large pipes this is generally adhered to. In small sizes it is common practice to use straight taps and taper dies, which has the effect of making the joint at the outside of fitting only. Calk here Calk here Makes Tight Joint here Any kind Fitting Derry Collard Co Figure 19. Suggested method of fitting pipes. A method has been proposed which seems to have several good points for all sizes of pipe. The plan is to use a taper tap, but have the pipe thread straight, so as to bring the tearing on the end of pipe. This being thin will force into a good contact, and also allow a good chance to calk the fitting around the pipe. The latter applies especially to large wrought iron fittings. This plan is shown in figure 19 as above. 19 One Way of Designating Tapers. As tapers are sometimes given as i in 2 or i in 4, the table below may be of use in reducing them all to tapers per foot. The taper in all cases given is the total taper between the sides of the piece. Taper of 1 in 2=6 inches to the foot " 3=4 <( n " 4=3 a (( " 5=2.4 ' (( (( " 6=2 (( (( " 7=1.71 ' (( (( " 8=1.5 ' I. i I " 9=1.33 ' it a "10=1.2 ' '• "■ "11=1.09 ' IC ki "12=1 ' n ^l V V T Morse Tapers. H e t3 c W e w n E "o E ni 5 w T3 C w E 5 0. « Q p C CO c W x; to c 4> — x; 1^ a: x: 4) Q m "0 -r) c Ofl c ClJ 3 .C H C (U .0 c 4J "5 e 5 aa c H >+-c 1/5 4) c :§ H to c H §