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 lAbrary 
 
 
ELEMENTARY 
 MACHINE =SHOP. PRACTICE 
 
 AS ADAPTED TO ITS TEACHING IN 
 
 TECHNICAL SCHOOLS 
 
 By T. J. PALMATEER 
 
 INSTRUCTOR IN MACHINE WORK 
 Leland Stanford Junior University 
 
 Copyright 1918 by T. J. PALMATEER 
 
 1918 
 
 Stanford University Press 
 
Library 
 
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 DEPT 
 
PREFACE 
 
 The instructions given in this book should meet the require- 
 ments of beginners in general machine shop practice. The main 
 object is to reduce as much as possible the time required to bring a 
 student with no previous shop experience to the point where he is 
 able to do some real work. The instructions given refer mainly to 
 the cutting of metal, since this usually gives the most trouble to 
 beginners. Little attempt has been made to describe the mechanism 
 of the different machines because it varies so much with the type 
 and make and is besides easily understood by the average student. 
 
 To obtain the best results with this book the following pro- 
 cedure is suggested. In most cases it can be carried out without 
 seriously interfering with the previously established work of the 
 school : 
 
 1. The instructor should give practical demonstrations for the 
 different exercises and actually perform those operations which he 
 considers necessary. 
 
 2. The student should study the instructions given herein dur- 
 ing his leisure time before and after the demonstration. 
 
 3. Each student should have a book for use in the shop so that 
 it may be consulted whenever necessary. This will help to develop 
 initiative. 
 
 4. A certain amount of time should be allowed to complete the 
 work. This should be enough to enable the average student to 
 finish on time. 
 
 Many thanks are due to H. P. Miller, Jr., for his helpful assist- 
 ance in the preparation of this book and to the following manu- 
 facturers for the half-tone illustrations : Smith & Mills Co., Sibley 
 Machine Co., and the Cincinnati Milling Machine Co. 
 
 T. J. PALMATEER. 
 
 Stanford University, Cal. 
 February, 1918. 
 
 735782 
 
PART I. 
 
 LATHE WORK 
 
ELEMENTARY LATHE PRACTICE. 
 
 EXERCISE No. 1 
 FIT SHAFT TO COLLAR RUNNING FIT 
 
 Machine Steel 
 
 Cut off with a power hack-saw a piece of steel 6 1/16 inches 
 long from a bar 1 inch in diameter. This will allow 1/16 of ari 
 inch for finishing the ends and 3/16 of an inch for turning the 
 diameter. 
 
 An experienced lathe operator would use a piece of steel 7/8 
 of an inch in diameter, but for beginners it is better to use larger 
 stock to allow for pi?a<kice -turning, 
 
 * CENTERING 
 
 Center both ends in the centering machine. The size of the 
 center in this shaft should be from 3/16 to 1/4 of an inch in 
 diameter. Larger work should have deeper centers. 
 
 ,'Drill and Countersink 
 
 Fig. i 
 
ELEMENTARY LATHE PRACTICE. 
 
 If a centering machine is not available, the work may be cen- 
 tered by first locating the. center with a pair of dividers and cen- 
 ter punch and then using a combination drill and countersink in 
 the lathe as shown in Pig. 1. In this case the work is held by 
 hand to prevent it from turning. As this work is to be turned, it 
 is necessary to center it only approximately true. 
 
 Accurate Centering'. When the work is to be centered accur- 
 ately, it may be done by putting one end in the lathe chuck and 
 the other in a steady rest. A pointed tool is then used in the tool 
 post as shown in Pig. 2. The po.nt of this tool has an angle of 60 
 degrees, the same as the lathe centers, and is ground like a flat 
 drill so that it cuts on both sides. 
 
 After the shaft is centered with this tool, a center hole about 
 1/8 of an inch in diameter should be drilled. This is done by 
 holding the drill in the tail-stock of tne lathe with a drill-chuck, 
 as shown in Fig. 3. The obj'.'c 1 : of this <;ent<^ hole is to give the 
 center of the shaft a bearing on the lathe center a short distance 
 back from the point, as at A in Pig. 4. 
 
 PLACING WORK IN LATHE 
 
 The work is made to rotate on the lathe centers by fastening 
 a lathe dog to the shaft at the head-stock end, as shown at A in 
 
 Head Stock 
 
 Fig. 5 
 
 Fig. 5. 
 
 The tail-stock center is adjusted so that the shaft Will rotate 
 freely, yet be tight enough to allow no slack, or lost motion. Since 
 the shaft rotates on this center, it should be kept well lubricated 
 by using machine oil, or a mixture of graphite and oil. 
 
 To get the best results in turning th.s sort of work, it is neces- 
 sary to face both ends before turning and to rough turn the whole 
 piece to within about 0.03, or 0.04 of an inch of the finished size 
 before any part of it is finished. However, it is not always neces- 
 sary to do this. The object of first rough turning the shaft all 
 over is to remove the internal strains of the steel and to wear the 
 centers down to a good bearing before any finshing cuts are 
 
ELEMENTARY LATHE PRACTICE. 
 
 taken. The purpose of facing the ends is to get them square, or 
 true, and smooth. 
 
 FINISHING END OF SHAFT 
 
 To face the ends, use a regular turning tool starting to cut 
 from the outside and feeding by hand towards the center with the 
 cross feed. Such a tool will leave a ridge near the center, as 
 shown in Fig. 6. This ridge is cut off with a sharp pointed, side 
 cutting tool, as shown in Fig. 7, which is also used for taking the 
 
 Fig. 6 
 
 finishing cut across the whole end of the bar. When taking this 
 finishing cut, lard oil, or some other lubricant, should be used. 
 
 After the finishing cut has been taken, any small ridge, or fin 
 that remains at the edge of the center is removed by slightly 
 changing the angle of the tool in the tool post and allowing about 
 ] 764 of an inch play between the centers. Having the work loose 
 like this when the lathe is running, allows the extreme point of 
 the side tool to extend beyond the edge of the center and cut a 
 smooth end. 
 
 The lathe should run slow for the finishing cut and fast when 
 the regular turning tool is used. 
 
 TURNING THE SHAFT 
 
 The first, or roughing cut, is taken with a high speed steel 
 tool, or bit, fastened in a tool holder. The tool holder is clamped 
 in the tool post of the lathe so that the point of the tool is at, or 
 a little above, the center, or axis, of the lathe, as in Fig. 8. 
 
 If the point of the bit is too high, it is easy to see that, as the 
 shaft rotates, the tool will not cut at all. Fig. 9. In case the tool 
 is set below the center, the cutting action is very poor so that 
 turning tools are never set as in Fig. 10. 
 
ELEMENTARY LATHE PRACTICE. 
 
 Fig. 8 
 
 fig. 9 
 
 Pig 10 
 
 Fig II 
 
 Turning Tool 
 
 Speed of the Lathe. In taking the heavy roughing cuts, the 
 belt may be placed on the second largest step of the cone, while 
 for the finishing cuts the lathe should run a little faster, say with 
 the belt in the next smaller step. 
 
 Grinding Turning Tool. The front, or point, and the sides of 
 the tool are ground at an angle, which is called the clearance. If 
 the tool has too little clearance, it will not cut freely, while if it 
 has too much clearance, the point will be so thin that it will break 
 off or become dull quickly. 
 
 The top of the tool is also ground at an angle. This is called 
 the rake. If the tool has too little rake, it will not cut freely and 
 if it has too much, the edge will soon break down. 
 
 It requires some practice for a beginner to learn the proper 
 rake and clearance that should be given to a tool. Fig. 11 shows 
 a tool ground with clearance and rake that will give very good 
 results. 
 
 Direction Tool Should Travel. The depth of the first cut 
 should be about 1/16 of an inch and the travel of the tool should 
 always be from the tail-stock end towards the head-stock. If the 
 travel is in the opposite direction, the pressure on the tail-stock 
 center is increased, causing it to heat quickly. 
 
 The length of the cut should be as great as possible without 
 the lathe dog striking the tool, or cross-rest. 
 
 Adjusting the Lathe to Turn Straight. After the first cut, 
 the work should be calipered and if it is not the same diameter 
 
ELEMENTARY LATHE PRACTICE. 
 
 at both ends the tail-stock should be adjusted so that the lathe 
 will turn straight 
 
 The tail-stock adjustment is made by loosening the main 
 clamping nut B and one of the screws C and then tightening the 
 other screw C on the opposite side of the tail-stock, Fig. 5. 
 
 If the shaft is larger at the tail-stock end, the tail-stock should 
 be moved towards the front of the lathe one half the difference 
 between the diameters of the shaft at the two ends. 
 
 In doing close work, the tail-stock should be adjusted as 
 closely as possible, but in this case if it is off center only a little, 
 say 0.002 or 0.003 of an inch, it will be close enough providing it 
 is set so that the shaft will be turned larger at the head-stock end. 
 If the tail-stock is set so that the shaft is turned larger at the tail- 
 stock end, the shaft will be too small at the other end after the 
 finishing cut is taken. 
 
 Fitting Shaft to the Collar. After the roughing cut is taken 
 and the lathe has been adjusted so that it turns approximately 
 stra ght, the end of the shaft is turned for about *4 of an inch so 
 that it w 11 just fit the hole in the collar, shown in the drawing 
 of Exercise 1. To measure this: first set the inside calipers to the 
 d'ameter of the hole in the collar, then set <he outside calipers to 
 the inside calipers and caliper the shaft as accurately as possible. 
 For a final test of this diameter, remove the work from the lathe 
 and try it with the collar itself. 
 
 The advantage of turning but % of an inch at the end of the 
 shaft is this; if the finishing cut were set too deep, only y of an 
 inch of the shaft would be too small, while if this cut were taken 
 the whole length, the entire shaft would be too small. 
 
 After the shaft has been turned at the end so that it fits the 
 collar, the rest of the shaft should be turned a little larger, say 
 0.002 or 0.003 of an inch, in diameter. This will leave enough to 
 finish with a file. 
 
 Filing. The object of filing is to take out the tool marks, but 
 it is also found to be much easier to make a close fit by filing off 
 the last 0.002 or 0.003 of an inch than to take so small a cut with 
 a tool. The amount of allowance for filing depends upon the 
 character of the finishing cut. Since the less filing required the 
 better, the finishing cut should be made as smooth as possible. 
 
 The tool used for the roughing cut may also be used for fin- 
 ishing, but it is usually necessary to re-sharpen it. After it is re- 
 set in the tool post, the point should be flattened a little wider 
 
10 
 
 ELEMENTARY LATHE PRACTICE. 
 
 than the pitch of the feed, say about 1/32 of an inch, and parallel 
 with the work. This is done with an oilstone. 
 
 For filing work -on a lathe, a single cut file is used. This is 
 called a lathe, or mill file. 
 
 u'^Ehe stroke of the file should be slow, steady, and straight 
 across the shaft. The lathe should run a little faster for filing 
 than for turning, the object being to have the work make several, 
 revolutions for a single stroke of the file. If the lathe runs too^ 
 slow and the stroke of the file is too fast, the shaft, instead of 
 be.ng filed round, will have a series of flat places on the surface. 
 
 After the work is finished as close to the dog as possible, re 
 verse it in the lathe and finish that part where the dog was fast- 
 ened. 
 
 
 EXERCISE No. 2. 
 
 f 
 
 t ~ 
 
 J" Toper 
 
 -1" par ft. 
 
 i' 
 
 t 
 
 _J _, 
 
 
 4. ' 
 
 The finished shaft in Exercise No. 1 may be used for Exercise * 
 >. 2. 
 
 Place the shaft in the bench vise and with a rule and scriber 
 ty off the dimensions; 1% iu- T 3 in., and l 1 /^ in. Then center 
 >unch the lines just deep enough so that they can be easily seen 
 r hen the work is in the lathe. 
 Turn the large end first. 
 When it is necessary to turn a fixed distance, or to a line a* 
 in this case, it is well to disconnect the feecT^flwm the tool is with- 
 in about 1/8 of an inch from the end of the cut and to feed the 
 tool the rest of the distance by hand. If this is not done, the tool 
 may travel farther than" it is intended to. 
 
 It is better to turn the portions to be threaded a little under 
 rather than over size. For if they are over size, the threads will 
 not fit the standard size nut, but if under size the threads do not 
 need to be cut so deep in order to fit the nut. 
 
 For measuring the diameters of this piece set the calipers as 
 
ELEMENTARY LATHE PRACTICE. 
 
 11 
 
 accurately as possible by measuring from the end of the rule, as 
 shown in Fig. 12. 
 
 Cutting 1 Recess. The surface at the end as well as the recesses 
 between the threads and the taper are cut with a square-nose, or 
 cutting-off tool, Fig. 13. 
 
 This tool shoull have a sharp smooth edge, the point being set 
 level with the center of the lathe. 
 
 To produce a smooth finished surface lard oil should be used 
 with a slow feed and lathe speed. 
 
 After the end is turned to size, reverse the work in the lathe 
 and turn the other end and the taper before cutting the threads. 
 
 Turning Taper. The drawing calls for a taper of 1 inch per 
 foot. This is cut by using a taper attachment, or by setting the 
 tail stock off center. As" most lathes are not provided with a 
 taper attachment, the latter method will be used. 
 
 If the worl$ was 12 inches long, the tail stock would be mov^d 
 off center 1/2 inch to turn a taper of 1 inch per foot. It being 
 only 6 inches Jong, the tail stock is set off center but half that 
 amount, or 14 inch. 
 
 Before taking the finishing cut, caliper both ends to prove 
 that the lathe is cutting the correct taper. 
 
 THREAD CUTTING 
 
 The threads are cut to fit i/2 i ncn an d 5/8 inch 'nuts having 
 United States Standard threads. These threads are flattened at 
 the top and bottom to the amount of 1/8 of the pitch instead of 
 eing sharp pointed as in the case of Standard V-threads. 
 
 Pitch. The pitch of the thread is the distance from the center 
 of one thread to the center of the one adjoining. On the end of 
 the exercise having 13 threads per inch the pitch is 1/13 of an 
 inch so that the width of the flat at the top and bottom of this 
 
12 
 
 ELEMENTARY LATHE PRACTICE. 
 
 thread should be 1/8 of 1/13 of an inch, or about .009 of an inch. 
 
 Lead. The lead of the thread is the distance a nut on the 
 screw will travel in making one complete turn. For single threads 
 the pitch and lead are the same, but for double threads the lead 
 is twice the pitch. 
 
 Grinding- Tool. The sides of U. S. S. threads form an angle of 
 60 degrees. To cut this thread in a lathe, a tool the same shape as 
 the threads is used. A gauge for grinding this tool accurately is 
 shown in Pig. 14. 
 
 fig. 14 
 
 Fig 16 
 
 If a U. S. S. thread gauge is not available, the tool can be 
 ground with the aid of a regular thread and center gauge, shown 
 in Fig. 15. With such a gauge the angle can be ground accurate- 
 ly, but it will be necessary to measure the flat point with a rule. 
 
 The top of the tool should be ground so that it will be approx- 
 imately in a horizontal plane when set in the lathe. 
 
 Where the thread to be cut is as fine as 13 per inch the flat 
 surface at the point of the tool is so small that the extreme point 
 can be oil-stoned off instead of being taken off with the grinding 
 wheel. The flat point should never be wider than the standard 
 size, but if it is a little too narrow it will make very little differ- 
 ence in ordinary lathe work. 
 
 Setting Tool. To set the tool so that both sides of the thread 
 will have the same angle, the thread gauge is used as shown in 
 Fig. 16. The tool should be set on a level with the center of the 
 lathe. 
 
 How Lathe is Geared. To cut 13 threads per inch the work 
 must make 13 revolutions while the carriage, which carries the 
 tool, travels one inch. For this purpose the lathe spindle is con- 
 
ELEMENTARY LATHE PRACTICE. 
 
 13 
 
 nected to the lead screw with the proper size gears and tfee lead 
 screw to the carriage by a split nut. This split nut is back of the 
 carriage apron and is opened and closed by the lever E, Fig. 17. 
 
 If the lead screw of the lathe has 6 threads per inch, the gear- 
 ing to cut 13 threads per inch must have the same ratio as 6 is to 
 13. To cut 16 threads the ratio would be 6 to 16. 
 
 It is not necessary to figure the size of gears for the different 
 
14 ELEMENTARY LATHE PRACTICE. 
 
 threads as all lathes are provided with an index plate that desig- 
 nates the proper size gears to be placed on the stud B and screw 
 C, Fig. 17, for the desired thread. 
 
 To Set Change Gear. To change these gears, first loosen the 
 nuts holding the stud and screw gears B and C. Next loosen the 
 nut G. This will allow the intermediate gear to drop away from 
 the stud gear B. Then loosen the nut H so that the intermediate 
 gear can be drawn back away from the gear on the lead screw C. 
 
 When the;- gears are put together, they should be set so that 
 there will be a little slack, or lost motion, between the different 
 gears. If they are set too close together, they will make a great 
 deal of noise when running and there is also danger of breaking 
 the teeth. 
 
 While all lathes are not designed alike the method of changing 
 the gears is very much the same on all machines, except those hav- 
 ing the quick change-gear device. With a lathe having such a de- 
 vice, instead of changing the gears on the stud and screw the same 
 result is obtained by shifting a combination of levers. 
 
 Why Feed Should Be Disconnected. The mechanism that 
 controls the feed, or travel, of the tool when cutting threads is 
 independent of that used for the feed when doing plain turning. 
 The two feeds usually run at different speeds so that if they are 
 both in action at the same time the gears in the carriage will 
 break. For this reason all lathes are provided with some means 
 of disconnecting the feed used for plain turning when cutting 
 threads. 
 
 To disconnect the feed on the lathe shown in Fig. 17, move the 
 lever J to the central, or neutral, position. This should always 
 be done before starting to cut the threads. 
 
 Speed of Lathe. The lathe should run slower for cutting 
 threads than for plain turning. With most lathes if the belt is 
 on the largest step of the cone it will give about the right speed 
 for cutting the threads in this exercise. 
 
 The object of running the lathe slow is to give the operator 
 time to draw back the tool at the end of the cut and to obtain a 
 smoother cut. If the speed of the lathe is too fast, the cutting 
 action will be so quick that the tool, instead of cutting clean and 
 smooth, will tear out the metal leaving a rough surface. 
 
 The slower the lathe runs the easier it is to cut the threads, 
 but it will also take longer to do the job. It therefore requires 
 
ELEMENTARY LATHE PRACTICE. 15 
 
 practical experience to determine the proper speed to be used for 
 cutting the different size threads. 
 
 Chamfering". After the lathe and tool are properly set, cham- 
 fer off the sharp corners where the threads begin and end with 
 the side of the thread tool. The depth of this cut should be about 
 the same as that of the threads when finished. If the corners are 
 not chamfered, the threads, when cut, will form a very thai edge, 
 or fin, at the ends. 
 
 of Adjustable Stop. To regulate the depth of each cut 
 an adjustable stop is used as shown at K. First move the tool so 
 that the point just touches the work, then adjust the screw on 
 the attachment K so that the cross-rest will not go in any farther. 
 Now move the carriage by hand until the point of the tool is a 
 little past the tail-stock end of the work ; close the split nut on 
 the lead screw with the lever E ; and turn the screw on the at- 
 tachment K so that the tool can be moved in just enough to take 
 a very light cut. 
 
 Start the lathe and when the tool has reached the end of the 
 cut back it out and reverse the lathe. By reversing the lathe the 
 tool is returned to the starting po.nt without disconnecting any 
 of the gearing. The object of drawing the tool back is to prevent 
 it from dragging on the work during its return. 
 
 The tool will never travel over the same path on the reverse 
 as on the forward movement of the lathe on account of the slack, 
 or lost motion, in the gears. 
 
 This first cut is taken to prove that the lathe is properly 
 geared, so the w r ork should be measured with a rule, or screw 
 p^tch gauge. 
 
 Adjust the screw at K until the tool can be moved in deeper 
 for the next cut and repeat the operation until the thread is 
 nearly finished. Then the tool should be reset so that it will cut 
 on only one side at a time. 
 
 Finishing Side of Thread. When roughing out the threads, 
 the tool cuts on both sides of the po.nt since it is fed straight into 
 the work. It is much easier, though, to finish the threads smooth 
 if the tool cuts on one side only. This is done by rapping the end 
 of the tool holder so that it is turned in the tool post just enough 
 to change the position of the point of the tool about .01, or .02 of 
 an inch. 
 
 To prove that the tool is set over the proper amount, turn the 
 
ELEMENTARY LATHE PRACTICE. 
 
 |w , 
 
 
 
 rwu'd by hand a tV\v rw 
 
 lathe forward by hand a few revolutions, to take out all the slack, 
 or lost, motion in the gears, then move the tool into the groove of 
 the thread until one side just touches the side of the thread. The 
 other side of the tool should then be about .01, or .02 of an inch 
 away from the side of the thread. 
 
 After the tool is properly adjusted, set the stop K. The tool 
 is then drawn back and the lathe reversed until the tool is at the 
 end of the work ready for a cut. Tt usually requires several fin- 
 ishing cuts to take out all the rough marks left by the roughing 
 cuts. 
 
 When this side of the thread is finished, the other side is fin- 
 ished in the sanfe' manner. 
 
 If the lathe^ provided with a compound . rest, a somewhat f 
 different procedure is usually followed since the rest can be set; 
 at an angle of 30 degrees with the work, as in Pig. 18. 
 
 In this case the tool is moved in by turning the small hand- 
 crank M until the side at hag, been cut to the proper depth. 
 While making these first cuts, the stop K is merely used to bring 
 the cross-rest to the same p^^oj^each time. The tool is then ^ 
 drawn back slightly with the hand-crank M and r the stop K ad- 
 justed so that the to$r can be moved straight in by means 
 hand-crank Q. This will finish the other side of the thread at P. 
 
 To determine when the thr-ead is cut to the proper size the 
 work is removed from the. lat^e and tested with a standard nut j 
 having IT. S. S. threads. 
 
 After the threads are cut on this end of the* exercise, -it is re 
 
 * \* 
 
 versed in the lathe and the other end threaded in a similar man- 
 ner. 
 
 To prevent the screw of the dog from marring the portion 
 already threaded two nuts should be screwed on and the dog fast- 
 ened to the nuts. 
 
 How to Reset the Tool. When cutting threads of this size and 
 larger, the tool usually becomes dull from taking the heavy rough- 
 ing cuts. It is then necessary to resharpen it before taking the 
 fine finishing cuts. 
 
 To reset the tool in the lathe first get the angles correct, as 
 shown in Fig. 16. Then revolve the lathe forward by hand to 
 take up the slack in the gears and move the tool in close to the 
 threads. If the tool is in a position so that it will cut too much 
 off one side of the thre^l^it may be changed by disengaging the 
 reversing gears with the liver R and turning the lathe by hand. 
 
ELEMENTARY LATHE PRACTICE. 
 
 17 
 
 When the tool is in the proper position relative to the groove of 
 the thread, the reverse gear lever R is reset. 
 
 In a case where the tool is off the desired position only a very 
 little, it may be corrected by the rapping process. 
 
 If the lathe has a compound rest the tool may be brought to 
 the correct position by turning the hand-crank M. 
 
 It would be well for beginners to practice thread cutting on a 
 piece of scrap steel before trying to cut them on the exercise. 
 
 EXERCISE No. 3. 
 CAST IRON FINISHED ALL OVER. 
 
 
 Sequence of Operations : 
 
 1. Finish the inside of Piece A. 
 
 2. Drill and Ream the hole in Piece B. 
 
 3. Mount B on mandrel and finish outside. 
 
 4. Screw A on B and finish the outside of A. 
 
 Piece A. 
 
 10 Thrds per 1" U.S.S. 
 
 2* -JM-i 
 
 Fig. 19 
 Rough Casting 
 
 Fig 20 
 Finished Casting 
 
18 
 
 ELEMENTARY LATHE PRACTICE. 
 
 USE OF 4-JAW CHUCK. 
 
 To machine the inside of piece A it is necessary to hold it in 
 the lathe by means of an independent four- jaw chuck, as shown 
 in Fig. 21. Work of this kind is usually chucked so that the out- 
 
 side surfaces will be within 1/32 of an inch of running true. 
 The process of chucking the work is as follows : 
 
 Centering Work in the Chuck. Place the work in the chuck 
 and adjust the jaws until they are all at approximately equal 
 distances from the circles on the face of the chuck. Then put a 
 cutting-off tool loosely in the tool post and move it close to the 
 work and as near as possible to the end of the chuck jaws. Re- 
 volve the lathe by hand to prove if the work is centered. If it is 
 not centered to within 1/32 of an inch, readjust the jaws until it 
 is. Now move the cutting-off tool to the end of the work and 
 turn the lathe by hand. If the end runs out of true, rap it with a 
 hammer at such po.nts as will correct its position. 
 
 Advantage of Proper Chucking. Fig. 21 shows the work held 
 by the middle step of the cone. One reason for holding it in this 
 way is to permit the rough turning of the larger step while in 
 the chuck. If the work were held by the small end, it would be 
 apt to work loose when taking the heavy roughing cuts on account 
 of the distance that the work projects out and the small diameter 
 on which the chuck grips compared with that of the large end 
 which is to be turned. 
 
 ROUGH TURNING AND BORING. 
 
 After the work has been properly chucked, rough turn the 
 end and the largest diameter to within 1/32 of an inch of the fin- 
 ished size. 
 
 All cast iron has a hard surface, or scale, from 1/64 to 1/32 
 of an inch deep so that it is necessary to run the lathe slower 
 for the first cut than for those made after the scale has been re- 
 
ELEMENTARY LATHE PRACTICE. 19 
 
 moved. In taking this first cut the tool should be set deep 
 enough to permit the point to cut under the scale. 
 
 Speed of Lathe. The speed of the lathe in taking the rough- 
 ing cut on work of this size should be about right if the belt is on 
 the smallest step of the cone and the back gears are used. After 
 the scale is removed, the lathe may be run faster. 
 
 A beginner will require experience before being able to de- 
 termine the proper speeds and feeds for the diffrent kinds of 
 lathe work. 
 
 Advantage of Roughing Inside. As the inside of piece A must 
 fit the outside of the piece B, the 1 1/8 inch hole, the threads, 
 and the taper must be machine true with each other, or else A will 
 not fit into B properly. Now if the taper should be finished and 
 the work moved in the chuck before the threads and the 1 1/8 
 inch hole are finished, they would not be true with each other. 
 For this reason it would be well to rough bore the inside to within 
 1/32 of an inch of the finished size before any of these three parts 
 are finished. 
 
 Roughing Inside. To rough bore the taper use a regular turn- 
 ing tool. Set the compound rest to the correct angle and feed the 
 tool in at that angle. 
 
 If the lathe is not provided with a compound rest, the taper 
 may be rough bored by turning both feeds by hand and following 
 the cored surface as closely as possible. 
 
 The cored hoie in the rough casting, Fig. 19, is 15/16 of an 
 inch in diameter which allows 3/16 of an inch for finishing the 
 1 1/8 inch hole and 5/16 for the portion where the threads are to 
 be cut. 
 
 Use of Flat Drill. To rough bore the hole a 1 1/16 flat, or 
 lathe, drill is used as shown in Fig. 21. The holder A is clamped 
 in the tool post so that the slot in it will hold the drill at the cen- 
 ter of the lathe. If the drill is held above or below the center, the 
 hole will be drilled larger than the drill. To prove that the slot 
 in the holder is at the center, move it close to the tail-stock center. 
 After the holder is properly set, move it as close to the work as 
 possible and feed the drill into the exercise by turning the hand 
 crank on the tail-stock. 
 
 This drill removes the hard surface, or scale, and also trues 
 up, or centers, the hole to within 1/64, or 1/32 of an inch. Now 
 enlarge the portion of the hole where the threads are to be cut 
 with a 1 3/16 drill. 
 I 
 
20 
 
 ELEMENTARY LATHE PRACTICE. 
 
 To determine when this drill has been fed in far enough, mark 
 on the drill with a piece of chalk the distance from the end of the 
 work to the point where the recess is to be cut. By sighting 
 across the end of the work the operator can then see when the 
 drill has been fed in the proper distance. 
 
 Use of Boring Bar. To cut the square shoulder where the 
 threads begin and the recess where they end, use a tool and boring 
 bar, as shown in Fig. 22, held in the tool post. The width of this 
 
 Fig. 22 
 
 u 
 
 tool is 5/32 of an inch so that it will be necessary to take two cuts 
 to make the recess w.de enough. Such a narrow tool is used be- 
 cause it is less liable to chatter. 
 
 This tool is ground with clearance at the sides as well as at 
 the front and it should also be noticed that it is wider at the cut- 
 ting edge than back close to the boring bar. This is done so that 
 when the tool is fed into the work there will be little, or no chance 
 of its binding on the side. 
 
 To obtain the correct setting for the tool, move the boring bar 
 into the hole and bring it up close to one side. The tool should 
 then be adjusted until its cutting edge is parallel to the elements 
 of this surface. 
 
 The work is now all roughed out so that it makes very little 
 difference which of the three fitting parts is finished first. 
 
 FINISHING INSIDE 
 
 The 1 1/8 inch hole has been drilled with a 1 1/16 inch lathe 
 drill, but as such a tool cannot be relied upon to drill true to cen- 
 ter, or size, it is necessary to turn it out with a boring tool. With 
 
ELEMENTARY LATHE PRACTICE. 
 
 21 
 
 this tool the hole can be bored true to center and within .01 of an 
 inch of the finished size. 
 
 The boring bar used in this case is the same as shown in Fig. 
 22, but the cutter has a rounded point and is similar to the tool 
 used for outside turning except that it is ground with less clear- 
 ance. 
 
 To insure accuracy and conserve time, the hole is then finished 
 with a shell reamer held in the lathe as shown in Fig. 23. 
 
 Reaming 1 the Hole. Before starting the reamer, the hole 
 should be bored at the end, for a distance of about 1/8 of an inch, 
 to the size which will just permit the reamer to enter. This dia- 
 meter must be calipered very carefully and should be tested with 
 the reamer itself. The rest of the hole is then bored about .01 of 
 an inch smaller in diameter to allow enough material for finish- 
 ing with the reamer. Since the reamer used in this case cuts on 
 the sides as well as on the end, the hole must be bored true to cen- 
 ter in order to be reamed true. 
 
 If the reamer has a tapered shank, it is held in the lathe by a 
 square shank socket and wrench, as shown in Fig. 23, and is fed 
 into the work by turning the hand-crank on the tail-stock. 
 
 In case the reamer has a straight shank, it is held as shown in 
 Fig. 24. Here a dog is fastened to the end of the reamer and pre- 
 
 vented from turning by a tool clamped at an angle in the tool- 
 post. The end of the tool presses against the dog near the shank 
 of the reamer so that as the reamer is fed into the work the car- 
 riage of the lathe is forced along with it. This causes the tool 
 
22 ELEMENTARY LATHE PRACTICE. 
 
 to hold the end of the reamer against the center of the tail-stock. 
 When reaming v. ork in a lathe, if the tail-stock is off center 
 the hole will be reamed too large at the front end. 
 
 Accurate Boring* with Boring Bar. In turning out holes with 
 a boring bar, if all the cuts are started from one end, that end will 
 be bored larger than the other. In case the hole is to be reamed, 
 the reamer will correct this, but if the hole is to be finished with 
 the boring bar it will be necessary to bore the hole from both ends. 
 Th s is done by reversing the feed of the carriage. 
 
 Speed of Lathe. The speed of the lathe for reaming should be 
 slower than when using the boring bar. If the belt is on the sec- 
 ond smallest step of the cone with the back gears in, the lathe 
 should ha\e about the right speed for reaming. When using the 
 boring bar, the belt should be on the largest step of the cone with- 
 out the back gear. 
 
 INSIDE THREADING 
 
 The inside threads are cut in very much the same manner as 
 the outside ones. The cutting tool is held In the boring bar and, 
 like all boring tools, is ground with less clearance than tools used 
 for outside work. 
 
 To regulate the depth of each cut, the screw in the adjustable 
 stop is placed between the stop and the cross-rest. Then by turn- 
 ing the screw in after a cut has been taken the cross-rest can be 
 draw r n back to permit a deeper cut with the tool. 
 
 Cause of Threads Breaking. When cutting threads in cast 
 iron, they will break if the roughing cuts are too heavy and are 
 liable to if they are cut to a sharp point. Another cause for the 
 breaking of cast iron threads is the use of a dull tool, or one with 
 too little clearance. 
 
 Finishing 1 Threads. As a general rule cast iron is machined 
 without using a lubricant, but in finishing threads a little lard oil 
 will aid in producing a smooth finish. 
 
 FINISHING ENDS 
 
 The end of the work may be finished by taking a very light 
 cut with the turning tool and then scraping it with a lathe scrap- 
 
ELEMENTARY LATHE PRACTICE. 
 
 23 
 
 er, as shown in Fig. 25. To provide a rest for the scraper a tool 
 
 is clamped in the tool-post and as close as possible to the surface 
 being scraped. 
 
 A scraper is usually made from an old file ground smooth on 
 the two sides and with a little clearance at the end. 
 
 FINISHING TAPER 
 
 
 To finish the taper, set the compound rest at an angle of 30 
 degrees with the axis of the lathe. Such a rest is normally 'at 
 right angles with the lathe axis so that it must be turned through 
 60 degrees to cut the 30 degree angle. A regular turning tool 
 may be used to finish this angle, but it should be set so that the 
 straight side will be nearly parallel with the tapered surface. 
 
 If the lathe is not provided with a compound rest, the angle 
 may be cut with the side of a tool set at the proper angle. To set 
 this tool, use the thread and center gauge, as shown in Fig. 26. 
 
 In case the angle is any other than 30, or 60 degrees, it is 
 necessary to set the tool with a bevel and bevel protractor. 
 
 After the taper has been cut, it may be finished smooth by 
 scraping with a lathe scraper in very much the same manner as 
 shown in Pig. 25. The tool that is used as a rest is set in as close' 
 as possible to the taper. If this rest is too far away from the sur- 
 face being finished, the scraper will chatter leaving a rough sur- 
 face. 
 
24 
 
 ELEMENTARY LATHE PRACTICE. 
 
 Piece B. 
 
 ** 10 Thrds pe 
 
 rj 
 
 f-H-l" 
 Rough Casting Fig. 27 Finished Casting 
 
 DRILLING AND REAMING. 
 
 This piece is f rst placed in the chuck, as shown in Fig. 28, 
 ind the end rough turned to see if it is a good casting. The hole 
 
 is then drilled with a 23/32 inch twist drill and reamed out to ' 
 size with a 3/4 inch rose reamer. 
 
 Centering Twist Drill. This drill will not bore a hole in the 
 center unless the point is controlled in some way. To do this, a 
 cutting-off tool is clamped in the tool-post with its point well/ 
 above the center of the lathe and is then moved close to the point'; 
 of the drill. As the drill starts to cut, it wabbles a Little on ac- 2 
 count of the po.nt being off center. The cutting-off tool is then ,, 
 gradually brought against the drill which is at the same time be-/ 
 ing slowly fed into the work by turning the hand crank on the . 
 tail-stock. It is necessary to have the drill centered true before it 
 begins to cut the full diameter. 
 
 The drill should <be placed in the tail-stock so that the cutting 
 edges are vertical. If they are horizontal, it will be difficult to 
 make the drill center/" 
 
 If the hole in this piece were larger, it would be cast with a 
 core and then machined in the same manner as the 1 I/Pinch hole 
 in piece A, but since it is cast solid, the hole can be machined 
 more advantage&usly by using a twist drill and a rose reamer. 
 
 Reaming. After the hole has been drilled with the 23/32 
 
ELEMENTARY LATHE PRACTICE. 
 
 25 
 
 ''dr JI-, Jbpre it out with a small boring tool for about 1/8 of an inch 
 from; the end to the diameter that will just fit over the reamer 
 iand insure its starting true. Ream the hole with the reamer held 
 in the same manner as the twist drill in Fig. 28. 
 
 Speed of Lathe. The lathe should run slower for reaming 
 than for drilling. The speed will be about right for this size 
 Y earner if the belt is on the largest step of the cone without the 
 back gears being used. The speed for the drill may be much 
 xfaster. With a high-speed steel drill, the belt can be run on the 
 second smallest step of the cone. If the drill is made of carbon 
 
 steel, a slower speed shoul.d be used. 
 
 u 
 
 Advantage of Rose Reamer. In drilling long holes like this, 
 ;he drill is very apt to get off center a little 'as it is fed deeper into 
 the work, even though it may have been started dead true. 
 
 The reamer used in this case is called a rose reamer, or rose 
 bit. and cuts on the end only. For this reason, if the hole is ap- 
 proximately true, say withm 1/64 of an inch, it will ream the hole 
 straight and true to size if it is once started true. 
 
 FINISHING CORNER 
 
 After the hole is bored and reamed, the work may be finished 
 
 ;at the end by using a tool ground like a threading tool, but hav- 
 
 l ;Shg an angle at the point a little less than 90 degrees, as in Fig. 
 
 m 
 
 Fig. 29 
 
 The boss, or hub, which is 1 3/8 inches in diameter, is finished 
 with one cutting edge of this tool set nearly parallel to the work, 
 vthe point being a trifle deeper than the rest. This will insure the 
 full depth of cut for the entire length and also a good sharp cor- 
 ner. The direction of feed for this tool should be from the end 
 and towards the square corner or shoulder. If it is fed in the op- 
 posite direction the tool is apt to chatter. 
 
 This tool is also used to finish the end, but it is turned a little 
 
26 
 
 ELEMENTARY LATHE PRACTICE. 
 
 in the tool-post so that the other cutting edge is nearly parallel 
 to the surface to be cut. After using this tool, the work may be 
 finished smoother by scraping the ends, as in Fig. 25, and by filing 
 the boss, or hub. 
 
 USE OF MANDREL, OR ARBOR 
 
 Before this piece can be finished on the outside, it must be 
 forced on a mandrel, or arbor, and placed in the lathe, as shown 
 in Fig. 30. Most commercial shops are provided with hardened 
 
 Fig. 30 
 
 V 
 
 steel mandrels for this purpose, but if one is not available it can 
 be made from soft steel in the following manner: 
 
 Making Mandrel. Cut off a piece of steel of suitable length, 
 say 6 inches, and rough turn it to within 1/32 of an inch of the 
 diameter of the hole. Then turn it at the end for a distance of 
 about 1/8 of an inch to the size that will just fit the hole. The 
 rest of the distance is now turned .002, or .003 of an inch larger 
 and filed for about 3 inches until it will just fit the hole. The 
 next 2 inches are filed with a slight taper so that when the man- 
 drel is pressed into the hole it will fit tight enough to hold the 
 casting while 't is being turned. This kind of a fit is called a 
 forced, or driving fit. 
 
 When making such a mandrel, it is not necessary to turn that 
 portion to which the dog is fastened. 
 
 Mounting 1 Work on Mandrel. Before pressing the mandrel in, 
 it should be oiled to prevent it from being marred, or scored.^ 
 Mandrels are usually forced in with a mandrel press, but if one 
 is not available, they may be driven in with a hammer. When 
 this method is used, a piece of lead, or some other soft material, 
 must be held on the end of the mandrel to keep the hammer from 
 marring the center. 
 
 FINISHING OUTSIDE OF PIECE B TO FIT A 
 
 This casting is rough turned to within 1/32 of an inch of the 
 finished size before any part of it is finished The 1 1/8 inch end 
 is then turned until it fits the corresponding part of the hole in 
 
ELEMENTARY LATHE PRACTICE. 
 
 27 
 
 piece A as closely as possible and yet not so tight that it cannot 
 be freely rotated. This kind of a fit is called a close running fit. 
 
 Cutting Threads. The portion to be threaded should be 
 turned a little smaller than the diameter at the bottom of the, 
 threads in piece A. This size is measured by means of the inside 
 spring-thread calipers. 
 
 There is no recess, or groove, cut at the end of this thread so 
 that if the threading tool is allowed to travel farther than the end 
 of the preceding cut. either the point of the tool or the threads 
 may break. To prevent this, the lathe is stopped when the tool is 
 within a half a thread of the end and the cut finished by turning 
 the lathe by hand. Tn this way the lathe is kept under control 
 and the tool may be drawn back when it reaches the end of the 
 preceding cut. Experienced lathe operators do not, as a rule, 
 turn the lathe by hand, but control the lathe entirely by the 
 shipper. 
 
 The speed of the lathe for cutting this thread will be about 
 right for beginners if the belt is on the second smallest step of the 
 cone and the back sresrs are thrown in. 
 
 Finishing 1 the Angle, or Taper. The 30 degree angle may be 
 cut by setting the compound rest to the correct angle and using a 
 regular turning tool. In case the tool leaves a few tool marks, 
 they may 'be removed by f-ling. 
 
 If the lathe is not provided with a compound rest, this angle 
 may be cut by sett ng a square-nose tool, as in Fig. 31, with the 
 
 Fig. 31 
 
 aid of a thread gauge. Any other angle would have to be set 
 with a bevel and bevel protractor. 
 
 This tool is not as wide as the surface to be cut because one 
 that will cut the full width is very liable to chatter. It is there- 
 fore better to make several cuts with a narrow tool. The surface 
 can then be finished smooth by filing. 
 
 The closeness of the fit of this taper with that in A can be 
 
28 ELEMENTARY LATHE PRACTICE. 
 
 tested Jby rubbing black paint, which consists of lamp black and 
 oil, on the tapered surface in A. When B is screwed into A, 
 marks will be made on B indicating the high spots. If these are 
 not loo high, they may be removed by filing. 
 
 FINISHING OUTSIDE OF PIECE A. 
 
 Piece A may now be screwed on B and the outside rough 
 turned to within 1/32 of an inch of the finished size. 
 
 The ends of the different steps are finished to the proper 
 length with the tool shown in Fig. 29. This same tool can then be 
 used to turn the different diameters to within 0.002 or 0.003 of an 
 inch of the required size. These steps are brought to the final 
 size by filing. 
 
 Filing. The file for this work should be less than 1 inch in 
 width. If it is wider than the steps, a beginner w r ill usually file 
 the portion at the end of each step smaller in diameter than that 
 which is close to the square corners. 
 
 The different diameters may be measured accurately with the 
 micrometer calipers. 
 
 KNURLING 
 
 After piece A is finished, it is removed from B and B is re- 
 versed in the lathe so that the boss may be knurled. 
 
 In case there is enough room between the dog and the work, 
 when held as in Fig. 30, there is no need to reverse the work for 
 knurling since it can be done in this position. 
 
 The boss at the end of B is used as a handle so that if it were 
 left smooth it would be hard to turn by hand. The surface is 
 therefore made rough with a knurling tool as shown in Fig. 32. 
 
 Fig. 32 
 
 The speed of the lathe should be about the same for knurling 
 as for thread cutting. If the lathe runs too fast, the knurling tool 
 does not cut satisfactorily. 
 
 The tool is set so that the face of the rollers is parallel with 
 
ELEMENTARY LATHE PRACTICE. 29 
 
 the surface to be knurled. When starting the cut, the rollers can 
 be forced into the piece easier if about half of their width extends 
 past the end of the work. 
 
 The knurling tool should be pressed into the work fast enough 
 so that about one half the depth of the finished knurl will be cut 
 while the lathe makes three or four revolutions. If the tool is 
 forced in too slow, it will cut a finer knurled surface than the roll- 
 ers are intended to cut. 
 
 The tool is fed along the surface in the same manner as in plain 
 turning. The speed at which the carriage of the lathe moves has 
 no effect upon the pitch of the knurled surface since this is con-' 
 trolled by the pitch of the grooves in the rollers. If a finer knurled 
 surface is desired, a knurling tool having rollers with finer grooves 
 would have to be used. 
 
 -^H 
 
 
 
 
PART II. 
 
 VISE, SHAPER, DRILLING AND TAPPING 
 
ELEMENTARY MACHINE SHOP PRACTICE 
 
 VISE WORK 
 
 Although most of the metal cutting in the machine shop can be 
 done by machine, it is sometimes necessary, even in the most 
 modern shops, to do some of it by hand. In order to give the 
 student practice in this hand, or vise work, the sides A and B of 
 the cast iron block, Fig. 1, are to be finished by chipping, filing and 
 scraping. 
 
 EXERCISE NO. 4 
 
 CAST IRON BLOCK 
 
 A A 
 
 B 
 
 -3ft 
 Fig. 1 
 Sequence of Operations: 
 
 1. Chip and file side A. 
 
 2. Scrape side A true to a surface plate. 
 
 3. Chip and file side B square with A. 
 
 4. Scrape side B true to surface plate. 
 
 Chipping. The original surface of cast iron is very hard for a 
 depth of about 1/64 of an inch and is almost impossible to file. It 
 is therefore necessary to remove this hard scale with chisels before 
 starting to file. 
 
 For this sort of chipping, cape and flat chisels, Figs. 2 and 3, 
 respectively, are used. 
 
 
 Fig. 4 
 
6 ELEMENTARY MACHINE SHOP PRACTICE 
 
 Parallel grooves are first cut in the surface as shown in Fig. 4. 
 These grooves must be just deep enough to get under the scale, i. e., 
 not less than 1/32" nor more than 1/16" deep. When they have 
 been cut to within 1/4 of an inch of the end, the direction of chip- 
 ping should be reversed to prevent breaking out the cast iron at the 
 corner. 
 
 The grooves should be uniformly spaced, in this case, about 1/4" 
 to 5/16" apart. On heavier work, where larger chisels are neces- 
 sary, the grooves are cut further apart. Generally the distance be- 
 tween the grooves should be about equal to the width of the cape 
 chisel used. 
 
 Care should be taken not to chip one portion of the surface 
 deeper than another ; the more uniform the grooves the less will be 
 the filing required to make the surface straight. 
 
 The metal ridges' are chipped off with the flat chisel shown in 
 Fig. 3. 
 
 Sharpening the Chisels. To do good work the chisels must be 
 kept sharp by grinding on a fine grinding wheel.. Care should be 
 taken not to hold them too hard against the wheel, thus drawing 
 the temper. 
 
 If the chisels are to be used for very light cuts, say 1/64 of an 
 inch deep, the cutting edge may be ground to a smaller angle than 
 is shown in Figs. 2 and 3. 
 
 FILES AND FILING 
 
 Files. While there is a large variety of shapes and sizes of files 
 manufactured," only" the ones to be used on these exercises will be 
 described. Students desiring further information on files should 
 consult the catalogue of some standard file manufacturer. 
 
 Files are designated by their size, type, and the coarseness or 
 cut of their teeth. 
 
 The size refers to the distance from the end of the file to the 
 point where the tang begins, Fig. 5. 
 
 The type refers to the general shape of the file. Those most 
 commonly used in a machine shop are the mill, flat, Hand, square, 
 round and half-round files. 
 
 The mill, flat and hand files are very similar in shape, but differ 
 from one another in detail. 
 
ELEMENTARY MACHINE SHOP PRACTICE 
 
 
 Flat 
 
 Hand 
 
 Fig. 5. 
 
 The mill file is uniform in thickness, tapered in width and is 
 single cut, i. e., has only one course of teeth. It is used principally 
 for lathe work. 
 
 The flat file is tapered in both width and thickness and is double 
 cut. It is intended mainly for general use and is not suitable for 
 lathe work. 
 
 The hand file is uniform in width, tapered in thickness and 
 double cut. It is a little wider than the mill and flat file and has 
 one safe edge, i. e., one edge without teeth. 
 
 The advantage of this safe edge is that the file may be used close 
 up to a square corner without cutting in at the side. This file is 
 preferred by machinists for flat surfaces, although the flat file may 
 also be used for such work. An edge of a flat file may be made 
 safe by grinding off the teeth. 
 
 The common square file is tapered and double cut. It is used 
 for filing square and rectangular holes and on square corners. For 
 this kind of work one edge should be safe. 
 
 The common round file is tapered and double cut. It is used for 
 filing round holes, concave surfaces, etc. 
 
 The half-round file is tapered and double cut. It is used on 
 large round holes, concave surfaces and acute angles. The latter 
 use is illustrated in Fig. 31, page 25. 
 
 The coarseness or cut of a file refers to the spacing of the teeth. 
 The three different spacings, or cuts, in common use are the bastard, 
 
8 ELEMENTARY MACHINE SHOP PRACTICE 
 
 second cut and smooth. Practically all of the common files may be 
 obtained in any of these three cuts. 
 
 Filing. Having removed the scale on the cast iron block with 
 chisels, the surface should be filed approximately straight with a 
 hand bastard file. If a hand file is not available a flat file may be used. 
 
 In the first rough filing, a full stroke of the file is used, but as 
 the surface approaches a true plane this may be changed to a short 
 stroke. A short stroke makes it easier to control the file. Rock- 
 ing the file should be avoided as it causes the edges and corners 
 of the work to be filed lower than the center. 
 
 To test the straightness of the surface being filed the edge of a 
 steel rule is held on it in several positions. 
 
 When filing work of this kind it is advisable to file in different 
 directions, i. e., parallel with one edge, crosswise and diagonally. 
 
 The teeth of all files are made to cut on the forward stroke. For 
 this reason the pressure should be relieved on the return or back- 
 ward stroke. 
 
 It will be noticed upon sighting along the edge of a hand file 
 that the thickness does not taper uniformly, both sides being slight- 
 ly convex. The curves are supposed to be uniform, but the warping 
 that occurs in tempering causes greater convexity at one place than 
 another. By using the file at the point of greatest convexity and by 
 giving it a short stroke the work may be filed straight even though 
 the file does rock a little. If the file is warped to the extent that 
 one side is slightly concave it will be impossible to file the work 
 straight with that side. 
 
 After the surface has been filed straight with the coarse or bast- 
 ard file it is finished smoother with a hand or flat smooth file. In- 
 stead of filing in different directions, as in rough filing, the strokes 
 should be parallel with one edge of the work. This causes all the 
 scratches or lines made by the file to be parallel, giving the surface a 
 better appearance. If it is to be scraped, as in this case, this will also 
 make it much easier. 
 
 When filing cast iron the file dust should never be brushed off 
 the work with the hand, as the hand deposits more or less grease, 
 causing the file to slip and dull quickly. Machinists usually blow 
 off the dust. When filing wrought iron or steel, oil or grease does 
 no harm, in fact oil is sometimes used to produce a smooth finish. 
 
ELEMENTARY MACHINE SHOP PRACTICE 
 
 SCRAPING 
 
 After the surface A has been filed smooth and approximately 
 straight, it is finished to a plane surface with a surface plate and 
 scraper. 
 
 Use of Surface Plate. To locate the high places on a flat 
 surface a surface plate, Fig. 6, is used. The size of the plate is 
 usually a little larger than the surface being scraped. The side A 
 is first covered with a thin film of paint made of lamp black and 
 lard oil. It is then placed in contact with the surface to be scraped 
 and moved around over it, marking the high spots. 
 
 A 
 Fig. 6 
 
 The paint should be spread on the plate with the finger tips and 
 just thick enough to cover it. If waste or cloth is used, lint is de- 
 posited on the plate and interferes with the marking. If it is spread 
 on too thick, the low places will be marked as well as the high ones. 
 
 It is very easy to locate the high spots if the work is a little 
 concave, but if a little convex the plate is apt to rock when moved 
 over the surface, thus marking the low as well as the high spots. 
 This makes it very important to use as little paint on the surface 
 plate as possible, and to move it over the work without rocking. 
 
 After locating the high spots the scraper is used on them and 
 the work again tested with the plate. These operations are re- 
 peated until the surface is true. 
 
 Use of the Scraper. In use the scraper is held firmly with both 
 hands at about the angle shown in Fig. 7. The cutting is done by 
 
10 ELEMENTARY MACHINE SHOP PRACTICE 
 
 holding it down hard on the work and moving it forward in the 
 direction indicated by the arrow. If the handle is held too high or 
 too low the scraper will not cut satisfactorily. A little practice will 
 be required before a beginner can properly control it. 
 
 Fig. 7 
 
 When using the scraper it will be noticed that it has a tendency 
 to chatter, causing a slightly wavy line cut instead of a smooth one. 
 If all the scraping is done in one direction these chatter marks be- 
 come deeper. This may be avoided by varying the direction of the 
 scraping a little after each marking with the surface plate. 
 
 The scraper is usually made from an old 10-inch file by grinding 
 off the teeth and forging it to the shape shown in Fig. 8. 
 
 Grinding the Scraper. After forging and hardening, the 
 scraper is ground straight on the side B, Fig. 8, and slightly convex 
 across the end A. If the latter edge is curved too much, the scraper 
 will take too narrow a cut, while if it is perfectly straight the cut 
 will be so wide that it will not be smooth. The scraper should be 
 ground so as to take a cut about 1/4 of an inch or wider. 
 
 The edge C should be ground at right angles with the center 
 line of the scraper. 
 
 Caution. The scraper is made of carbon steel and is tempered 
 very hard. Beginners are therefore cautioned not to draw the tem- 
 per by grinding it too fast. This often happens without being 
 noticed so that the beginner is unable to understand why his scraper 
 will not cut. 
 
ELEMENTARY MACHINE SHOP PRACTICE 
 
 11 
 
 A C 
 
 
 
 B 
 
 
 B 
 
 
 
 5" 
 
 f 
 
 
 i 
 1 
 
 K r 
 
 .1.. 
 
 Fig. 8 
 
 Fig. 9 
 
 Fig. 10 
 
 Oilstoning the Scraper. The grinding wheel produces a some- 
 what rough cutting edge which must be oilstoned before the 
 scraper will cut smoothly. This oilstoning is done by moving the 
 end and the sides of the scraper alternately over the surface of a 
 flat oilstone. 
 
 When oilstoning the end it may be held vertically, Fig. 9, or at 
 a slight angle, as in Fig. 10. If held at an angle the sharpening is 
 done a little quicker and the edge will be slightly beveled. Such an 
 edge will cause less chattering than the one obtained by oilstoning 
 as in Fig. 9. When one edge has been sharpened the scraper is 
 turned over and the other edge sharpened in the same manner. 
 
 Fig. 11 shows the correct position for oilstoning the side. The 
 handle should not be raised, as in Fig. 12, as this would take off 
 the sharp edge. A fine wire or feather edge is produced, no matter 
 how hard the scraper is tempered. To take advantage of it, the 
 scraper should be oilstoned on the side last if it is to cut on the 
 
12 
 
 ELEMENTARY MACHINE SHOP PRACTICE 
 
 forward stroke, as in Fig. 7, and on the end last if it is to cut on the 
 draw stroke. 
 
 Fig. 11 
 
 Fig. 12 
 
 In order to do good work the scraper must be kept very sharp. 
 It will be necessary to oilstone it several times while scraping the 
 surface of this exercise. 
 
 When the scraper has been repeatedly oilstoned so that the cut- 
 ting edges are worn off, the end should be reground on the grind- 
 ing wheel to the original shape, as shown at C in Fig. 8. 
 
 Finishing Side B. After side A of Exercise 4 has been finished, 
 the side B is squared with A by the same process, i. e., by chipping, 
 filing and scraping. 
 
 If B is very much out of square with A, one side of B may be 
 chipped a little deeper than the other. In doing this it will be better 
 to take several light cuts with the cape chisel than to try to remove 
 too much metal in one cut. Too deep a cut will cause the edge of 
 the chisel to break. 
 
14 ELEMENTARY MACHINE SHOP PRACTICE 
 
 SHAPER WORK 
 
 An up-to-date shaper is shown in Fig. 13. The four-step cone 
 drive with back gears gives eight speeds. Two sides as well as the 
 top of the table are provided with slots for clamping work that is 
 too large to be held in the vise. 
 
 The table may be raised or lowered by means of the hand crank 
 shown at the end of the cross-rail. By placing this crank on the 
 shaft immediately above it the table may be fed horizontally by 
 hand. 
 
 The automatic table feed is started, stopped or reversed by 
 means of a small knobbed pin which engages the ratchet gear at the 
 end of the cross-rail. The rate of feed is varied by changing the 
 position of a large knobbed pin on the disc near the driving cone. 
 The hand crank above this disc is used for changing the length of 
 the stroke. The position of the stroke is changed by loosening the 
 lever on top of the ram and turning the squared shaft shown near 
 the head of the ram. 
 
 Shapers are usually designated by their maximum length of 
 stroke ; as, a 16-inch or a 20-inch shaper. 
 
ELEMENTARY MACHINE SHOP PRACTICE 
 
 15 
 
 Fig. 13 
 20-INCH SHAPER 
 
16 
 
 ELEMENTARY MACHINE SHOP PRACTICE 
 
 EXERCISE NO. 5 
 
 PLANING ONE SURFACE SQUARE WITH ANOTHER 
 
 Sequence of Operations: 
 
 1. Clamp in shaper vise and plane side D square with A. 
 
 2. Plane the ends E and F square with the sides A, B, and D. 
 
 In taking up the exercise on the shaper it is assumed that the 
 sides A and B of the cast iron block in Fig. 14 have been finished 
 true and square in the vise. The other sides are to be finished on 
 the shaper to the dimensions given. 
 
 First lay off the width of the side C with a scriber and combina- 
 tion square, as shown in Fig. 15, marking a line 2 5/8 inches from 
 the side B and parallel with it. In order to make the scriber marks 
 plainly visible the surface should be chalked. This is especially 
 necessary when the hard scale has not been removed. 
 
 15 
 
 Clamping the Work. The work is clamped in the shaper vise 
 
 with the finished side B resting on the base and with the side A 
 
 against the stationary jaw of the vise, as in Fig. 16. A piece of 
 paper should be kept under each end of B. 
 
ELEMENTARY MACHINE SHOP PRACTICE 
 
 17 
 
 The clamping bolt J may be left loose until the jaw is close to 
 the work. It should then be tightened so that as the jaw is screwed 
 up against the work it will not be raised off the base of the vise. 
 
 D 2 
 
 " J 
 
 Fig. 16 
 
 The narrow metal strip shown at H should be about 1/16" x 
 1 /2" x 6". It is used so that when the vise is tightened the pressure 
 on the block will be about at the center. This holds the side A tight 
 against the solid jaw. By rapping side D with a hammer B is 
 forced down on the base of the vise until the paper at both ends is 
 tight. 
 
 The work is now ready for the roughing cut. This is taken 
 with a tool or bit similar to the one used on the lathe, but which 
 has less clearance since it cuts along a straight line. The lathe 
 tool holder is sometimes used on the shaper, but a regular shaper 
 tool holder, Fig. 17, is preferred. The latter has an adjustable 
 head or clamp so that the tool may be turned at different angles. 
 The piece of tool steel used in such a holder should always be longer 
 than the diameter of the head, otherwise it will not be held firmly. 
 
 Depth of Cut. The depth of the roughing cut depends mainly 
 upon the size of the machine and the amount of metal to be removed. 
 If 1/8 of an inch is to be cut off take a little more than half that 
 amount the first cut. 
 
 Rate of Feed. This also depends largely upon the size of the 
 machine. With large and heavy machines deep cuts may be taken 
 and coarse feeds used. 
 
18 
 
 ELEMENTARY MACHINE SHOP PRACTICE 
 
 [ J 
 
 Fig. 17 
 
 Fig. 18 
 
 If a small shaper is used, as is generally the case with work of 
 this sort, the rate of feed with a cut about 1/8" deep, may be about 
 1/64 of an inch. With a cut only 1/16" deep the feed may be in- 
 creased to 1/32" per stroke. 
 
 Testing the Work for Squareness. After the first roughing 
 cut, a finishing cut is taken and the work removed from the vise. 
 It is then tested with a square to make sure that the surface being 
 machined is square with side A. The stationary jaw cannot be de- 
 pended upon to hold the work square. 
 
 The finishing tool, Fig. 18, is forged from a piece of carbon steel. 
 Care should be used in grinding it not to draw the temper. The 
 advantage of using carbon steel instead of high speed steel for this 
 tool is that it makes a smoother finishing cut and is cheaper and 
 easier to forge. The cutting edge should be ground as straight as 
 possible. It may be a little convex but never concave. The clear- 
 ance angle B should be about 10 or 15. 
 
 Setting the Finishing Tool. In order to take a smooth finish- 
 ing cut, the tool should be set with the cutting edge parallel, or 
 nearly so, with the surface to be planed. This is done by clamping 
 it loosely in the tool post and over but not touching the work. If 
 the cutting edge is not parallel with the work, rap the tool until it 
 appears to be so. Feed the tool down with the hand crank until it 
 
ELEMENTARY MACHINE SHOP PRACTICE 
 
 19 
 
 just touches the work. Now move the ram of the shaper forward 
 by pulling the belt by hand. The fine chip or dust removed by the 
 tool will show if it is set in the proper position. 
 
 Direction of Feed. If the tool appears to cut deepest at the 
 center, it may be fed in either direction, Fig. 19, but if it is set so 
 that one side cuts slightly deeper than the other, as in Fig. 20, the 
 direction of the feed should be as indicated by the arrow. Feeding 
 in the opposite direction is apt to make the tool chatter because of 
 the wide cutting edge that is in contact with the work. 
 
 Fig. 19 
 
 Fig. 20 
 
 The curve of the cutting edge in Fig. 19 and the angle at which 
 the tool is set in Fig. 20 are greatly exaggerated. The cutting edge 
 should be straight within .002 or .003 of an inch and one side should 
 not be set more than .002 or .003 deeper than the other. 
 
 Depth of Finishing Cut. The finishing tool is intended for 
 shallow cuts of not more than .01 of an inch and works better if still 
 less is taken. In general practice it is customary to plane to the 
 finish line with a roughing tool and use the finishing tool merely to 
 remove the marks of the roughing tool. If .02 or .03 of an inch 
 are to be removed several cuts should be taken. 
 
 Rate of Feed. As the finishing tool has a wide cutting edge a 
 coarse feed may be used. In this case about 1/8 of an inch per 
 stroke will do. With most shapers this is about equivalent to one- 
 half turn of the hand crank. The feeding should be done by hand 
 and care taken to note the position of the crank after each turn. 
 This insures a uniform rate of feed. 
 
 Resetting Work. After the first finishing cut, the work is 
 removed from the shaper vise and tested to see if the sides A and 
 D are square with each other and if side D is parallel with B, Fig. 
 
20 
 
 ELEMENTARY MACHINE SHOP PRACTICE 
 
 16. In case D is not square with A the setting in the vise may be 
 corrected, within certain limits, by having the metal strip H higher 
 or lower. When this strip is near the top of the vise the block will 
 be very slightly tipped so that the edge 2 will be a little higher 
 than 1. With H at or close to the bottom the effect will be just the 
 opposite and a little more metal can be cut off at edge 1 than at 2. 
 
 If the two sides B and D are not parallel additional pieces of 
 paper may be placed under the thickest end. 
 
 It may be necessary to take several trial cuts before the block 
 is properly set in the vise. These cuts should be taken with the 
 finishing tool since it is quickly fed across the work and does not 
 remove much metal. 
 
 The work is now machined to the finished size. If it is neces- 
 sary to remove more than 1/32 of an inch of metal, time will be 
 saved by first using the roughing tool, as the finishing tool is not 
 intended to take more than .01" per cut. 
 
 Planing the End. To plane the end of the block it is held in 
 the vise .in the same manner as when planing side D. It is first set 
 approximately straight by using the square as in Fig. 21. In this 
 view the solid jaw of the vise is not shown. 
 
 The base of the vise cannot be relied upon to be parallel with the 
 travel of the tool so that a trial roughing and finishing cut should 
 be taken to test the squareness of the surface E with the sides B 
 and D. 
 
 Fig. 21 
 
 If the block is not set square it may be tilted a little in the vise 
 by holding the grain end of a piece of wood against one corner and 
 
ELEMENTARY MACHINE SHOP PRACTICE 21 f 
 
 rapping the wood with a hammer. Another trial cut should then be 
 taken and the process repeated if it is not square. 
 
 To Prevent Corners from Breaking. It will be noticed that 
 both the finishing and roughing tools break off the corner of the 
 work at the outer end of the cut. To prevent this the corner is 
 filed off at an angle of about 20 with the surface being planed, and 
 as deep as the finishing cut is to be. 
 
 On work of this size the corner should be filed off when the sur- 
 face has been planed to within 1/32 or 1/16 of an inch of the finished 
 size. The important thing is to be sure to file off the corner before 
 it breaks out deeper than the finished size. 
 
22 
 
 ELEMENTARY MACHINE SHOP PRACTICE 
 
 
 Fig. 22 
 
 PLANING ONE SURFACE PARALLEL WITH ANOTHER 
 AND PLANING ANGLES 
 
 2. 
 3. 
 
 4. 
 
 5. 
 
 Sequence of Operations: 
 
 1. Lay off on one end of block the outline of the finished piece. 
 Clamp in vise, Fig. 23. 
 
 Plane side C to size with roughing and finishing tools. 
 Rough out the angles with a roughing tool, Figs. 24 and 25. 
 Finish the angles. 
 
 In laying off the outline of the finished piece the combination 
 square can be used, as before, for the measurements and to mark 
 the 90 angle. A thread gauge or a bevel protractor is used for the 
 60 angle. 
 
 Clamping in Vise. The work is clamped in the vise as shown 
 in Fig. 23. The parallels J and K are longer than the work and 
 high enough so that the jaws of the vise grip on about 1/2" of the 
 work. The object in clamping on only a small area of the sides is 
 to make it easier to rap the work down on 'the parallels. 
 
 C 
 
 B 
 
 .-- Fig. 23 
 
 Clamp the work tight, and rap the top with a hammer to force 
 it down tight on the parallels. 
 
 5 
 
ELEMENTARY MACHINE SHOP PRACTICE 
 
 23 
 
 % 
 
 Planing One Side Parallel with Another. After taking a 
 roughing and finishing cut, caliper the block at each corner to see if 
 it is uniform in thickness. If one corner is thicker than another, 
 place one or more pieces of paper under that corner and take an- 
 other trial cut. This operation is repeated until the sides A and C 
 are parallel. 
 
 Roughing Out the Angles. The angles are roughed out with 
 the regular roughing tool, cutting as close to the lines as possible. 
 These roughing cuts should be heavy so as to remove the metal 
 quickly. The tool should be started at the outside and fed toward 
 the center. If the automatic feed is used it should be disengaged 
 when the tool is within about 1/16 of an inch of the finish line. 
 When roughing out the angles, set the head, clapper box and tool 
 as in Figs. 24 and 25. 
 
 Setting the Head, Clapper Box, and Tool. Loosen the clamp- 
 ing screw N, Fig. 24, and move the clapper box to about the angle 
 shown. The side of the tool should be nearly vertical as at 0. 
 
 Setting the clapper box at this angle causes the tool to swing 
 way from the vertical side of the work on the return stroke of the 
 aper. If it were set at the opposite angle it would swing into the 
 work. 
 
 
 Fig. 24 
 
24 ELEMENTARY MACHINE SHOP PRACTICE 
 
 For the 60 angle set the head to an angle of 30 with the verti- 
 cal, using the graduations on the quadrant of the head R, Fig. 25. 
 Move the clapper box to about the angle shown. It should be 
 noticed that the angle at which this is set is just the opposite of the 
 one used when cutting the 90 angle. This is because the tool is 
 to cut on the opposite side. 
 
 R 
 
 Fig. 25 
 
 Finishing the 60 Angle. The tool for finishing the angle is 
 ground a little less than 60, and with cutting edges on the side and 
 bottom, L and M, Fig. 26. 
 
 First adjust it so that the bottom edge is nearly parallel with the 
 top of the block as at I in Fig. 27, being sure that the point is 
 slightly deeper, say, about .001 of an inch, than the rest of the tool. 
 To prove that this is so, pull the belt by hand with the tool just 
 touching the work. The deepest part of the tool will remove a small 
 chip or some dust. 
 
 Move the tool to the side of the angle at G and feed it down with 
 the hand crank to remove the round corner left by the roughing 
 tool. Finish the bottom by feeding the tool from the outer edge 
 into the corner. The point of the tool being set deeper insures the 
 full depth of the cut to the sharp corner. 
 
 Start a cut from the top of the 60 angle and feed down to the 
 bottom. Now adjust the tool so that it is nearly parallel to the 
 side as at H in Fig. 28, being sure that the point cuts the deepest. 
 
ELEMENTARY MACHINE SHOP PRACTICE 
 
 25 
 
 Take a finishing cut beginning at the top and feeding down until 
 the point just touches the bottom. 
 
 ~\^U 
 
 Fig. 26 
 
 Fig 28 
 
 This tool, like practically all finishing tools, should be kept sharp 
 by grinding and oilstoning. It should not be used for cuts of more 
 than .01 of an inch in depth. 
 
 Finishing the Right Angle. When the 60 angle has been fin- 
 ished, the 90"~*angle is finished in about the same manner. The 
 head must be returned to its vertical position and the clapper box 
 tilted as in Fig. 24. The tool used is ground a little less than 90, 
 Fig. 30. 
 
 The bottom, or base of the angles, S and T, Fig. 30, should be 
 finished to the same level. To do this the tool is set so that it just 
 touches the surface T. The final finishing cut is then taken on S 
 without changing the height of the tool. 
 
 Filing the Angles. After the angles are machined they may 
 be finished smoother with a file. A 10-inch smooth square file with 
 a safe edge may be used for the right angle as at U, Fig. 31, and a 
 10-inch smooth half-round file for the 60 angle. The latter should 
 have a safe edge at V so it will not cut into the side when filing the 
 bottom. 
 
 X |U 
 
 Fig. 30 
 
 Fig. 31 
 
26 ELEMENTARY MACHINE SHOP PRACTICE 
 
 DRILLING AND TAPPING 
 
 The size of a drill press is determined by the maximum diam. 
 of the work which can be centered with the spindle. Hence on a 
 16-inch machine the distance from the center line of the spindle to 
 the column is about 8 inches. 
 
 A 16-inch drill press is shown in Fig. 32. With a five-step cone 
 it has five spindle speeds, ranging from 150 to 1700 revolutions per 
 minute. This makes it an excellent machine for light drilling. 
 Drills larger than 1/2 inch are not generally used. The spindle 
 feed is controlled by the hand lever at the side of the spindle. The 
 table may be raised or lowered by means of the hand crank on the 
 column. 
 
 Fig. 33 shows a 20-inch complete drill with back gears. It has 
 8 changes of speed, ranging from 25 to 300 revolutions per minute. 
 The back gears are located at the top of the machine and are shifted 
 by means of the lever shown directly beneath them. This machine 
 has both hand and automatic feeds and is also provided with an 
 automatic stop for drilling a number of holes of the same depth. 
 The drills used generally range from 1/4 inch to 1 1/2 inches, but 
 larger or smaller ones can be used. 
 
 When work is clamped to the table of the machine, it may be 
 moved to any desired position for drilling by rotating the table and 
 swinging the table arm about the column. To hold the table in 
 position the wrench shown underneath it and a similar one on the 
 column are tightened. 
 
 The Hi-Speed Drill Press shown in Fig. 34 is built a little larger 
 and heavier than the one just described. This machine will drive 
 drills of high speed steel up to 1 1/4 inches in diameter to their full 
 capacity. Eight changes of speed from 90 to 610 revolutions per 
 minute are obtained by means of the enclosed gears at the top of 
 the machine. It is also provided with hand and automatic feeds 
 and an automatic stop. 
 
ELEMENTARY MACHINE SHOP PRACTICE 27 
 
 Fig. 32 
 16-INCH DRILL PRESS 
 
28 
 
 ELEMENTARY MACHINE SHOP PRACTICE 
 
 Fig. 33 
 20-INCH COMPLETE DRILL 
 
ELEMENTARY MACHINE SHOP PRACTICE 
 
 29 
 
 Fig. 34 
 HI-SPEED DRILL PRESS 
 
30 
 
 ELEMENTARY MACHINE SHOP PRACTICE 
 
 EXERCISE NO. 7 
 
 Piece A is an unfinished cast iron plate. 
 Piece B is Exercise No. 6. 
 
 ' L.U 'A j J..i 
 
 jpl| 
 
 B P| 
 
 6 
 
 \ C 
 
 
 I 
 
 
 V 
 
 1 
 
 
 
 K 
 
 L 
 
 
 
 M 
 
 N 
 
 
 
 
 ^ 
 
 
 H 
 
 D 
 
 
 J 
 
 Fig. 35 
 
 Fig. 36 
 
 Sequence of Operations : 
 
 1. Grind the rough surfaces of piece A. 
 Lay off the centers for holes in piece A. 
 Drill 1/2 inch holes in piece A. 
 Place A on B and scribe position of holes on B. 
 Drill B with 13/32" drill 13/16" deep. 
 Tap holes in B with 1/2-inch U. S. S. plug tap. 
 Tap bottom of holes with 1/2-inch U. S. S. bottom tap. 
 If screws bind in holes of piece A file with round file. 
 
 2. 
 
 3. 
 4. 
 
 5. 
 6. 
 7. 
 8. 
 
 Grinding Piece A. As it comes from the foundry the cast iron 
 piece A is usually rough. It should be smoothed up on the grinding 
 wheel before laying out the holes. 
 
 Laying Out the Centers of the Holes. Piece A being a rough 
 and unfinished casting is not apt to be square or true to size. It is 
 therefore advisable to first mark the center lines CD and EF, 
 Fig. 36. 
 
 To do this the surface is first chalked to make the lines plainly 
 visible. Mark C and D at the center of the two ends and as close to 
 the ends as possible. Center punch them with a small center punch 
 and draw a line between them. With a pair of dividers and with 
 
ELEMENTARY MACHINE SHOP PRACTICE 31 
 
 C and D as centers describe the arcs which locate E and F. The 
 line through these two points will be at right angles with CD and 
 at its center. 
 
 Next mark with the dividers on each side of CD half of the total 
 distance between the centers of holes and draw GH and IJ. From 
 EF mark off on these lines the required spacing of the holes K, L, 
 M, and N. 
 
 To prove that the hole centers are laid out square, measure the 
 distance from L to M and from K to N with the dividers. Check 
 the layout with a rule to see if the centers are the correct distances 
 apart. 
 
 When the intersections are in the right positions for the hole 
 centers, mark them with a small center punch. Now scribe circles 
 about these points a little larger than the size of the holes to be 
 drilled so that after drilling it may be seen if the hole is in the right 
 position. 
 
 Holding the Work. This exercise being small in comparison 
 with the holes to be drilled, should be clamped to the table of the 
 drill press, Fig. 37, or held in a drill vise, Fig. 38. When the 
 former method is used, the work should be placed so that the drill 
 is above one of the slotted holes in the table. The object in this 
 is to avoid drilling into the table. In using the vise, the parallels 
 should not be directly under the drill. 
 
 Fig. 37 Fig. 38 
 
 If the holes were small, say less than 1/4 inch, or the casting 
 larger, it could be held by hand. In this case the work should 
 rest on a piece of wood. Since the wood is soft the work is less 
 liable to slip out of the hand than when placed on the smooth sur- 
 face of the drill press table. The slipping does not usually occur 
 until the point of the drill pierces through at the end of the hole. 
 Then it will slip unless held firmly. 
 
32 
 
 ELEMENTARY MACHINE SHOP PRACTICE 
 
 Selecting the Drill. Drills are usually designated by their size 
 and the shape of their shanks. The size refers to the diameter of 
 the drill. The shank is the end of the drill by which it is held in 
 the machine. 
 
 The common drill sizes as listed in most catalogues run from 
 1/16 of an inch to 3 inches, varying by 1/64 inch. The sizes usually 
 found in shops, however, run about as follows: 1/16" to 1/2" by 
 1/64", 1/2" to 1" by 1/32", 1" to 2" by 1/16". 
 
 Drills are also made in number and letter sizes. The number 
 sizes run from No. 1, which is .2280 in diameter, to No. 80, which 
 is .0135 in diameter. There are 80 different sizes. The letter drills 
 range from A, with a diameter of .234 inches, to Z, which is .413 in 
 diameter, and are 26 in number. 
 
 The shank of the common drill is either straight or tapered. 
 When straight it is held in the machine with a drill chuck. 
 
 Fig. 39 
 
 Taper shank drills are held in the spindle as shown in Fig. 39. 
 The tongue, or tang, of the drill, A, fits into a slot at the end of the 
 hole in the spindle and makes the drill rotate with the spindle. The 
 tapered shank keeps the drill from dropping out. To remove the 
 drill from the spindle, a taper drift, B, is used as shown. 
 
 The advantages of the taper shank drill are that it runs true and 
 is more conveniently held in the machine for large sized holes. 
 Straight shank drills larger than 3/4" must be held in a chuck so 
 large that it often interferes with the drilling. 
 
 In most shops drills up to 3/16" diameter are used with straight 
 shanks and those from 3/16" to 3/4" in diameter with either 
 straight or taper shanks. Drills larger than 3/4" in diameter usually 
 have taper shanks. 
 
ELEMENTARY MACHINE SHOP PRACTICE 
 
 33 
 
 Straight shank drills cost less than those with taper shanks and 
 are therefore used whenever possible. 
 
 
 
 Fig. 40 
 
 The steel sleeve or bushing shown in Fig. 40 is used when the 
 shank of a taper shank drill is smaller than the hole in the spindle 
 of the machine. Sometimes when using small drills in a large ma- 
 chine it is necessary to use two or three of these sleeves. 
 
 After selecting the drill examine the edges. If they are dull 
 sharpen them on the grinding wheel. 
 
 How the Drill Should Be Ground. The common twist drill 
 has two cutting edges A and B, Fig. 41. Like other tools these 
 must be ground with clearance C in order to cut when the drill is 
 forced into the metal and rotated as indicated by the arrow. 
 
 The cutting edges A and B should each make an angle of 59 
 with the axis of the drill. They should be of equal length in order 
 to bring the point of the drill in the center. If the point is off 
 center, only one edge of the drill will cut. This not only reduces 
 its efficiency but also produces a hole larger than it is intended. 
 
 Fig. 41 Fig. 42 
 
 There are two methods of sharpening a drill, by machine and by 
 
34 
 
 ELEMENTARY MACHINE SHOP PRACTICE 
 
 hand. In shops where a great deal of drilling is required, a drill 
 grinding machine is used. 
 
 Hand Grinding. When it is necessary to sharpen a drill by 
 hand, and especially one that is larger than 3/8", a drill grinding 
 gauge should be used, Fig. 42. 
 
 The cutting edge on smaller drills may be gauged by eye. If 
 the side of the grinding wheel is used instead of the periphery, it is 
 easier to produce a good cutting edge. 
 
 Speed of Drill. The speed of the drill depends upon its size, 
 the material being drilled and the feed used. 
 
 The following table will give beginners some idea of the range 
 of speeds for different sized drills made of carbon steel. 
 
 Diameter 
 of 
 Drill 
 
 Revolutions per minute 
 
 Soft Steel 
 
 Cast Iron 
 
 Brass 
 
 1/8 
 
 1/4 
 3/8 
 1/2 
 3/4 
 
 850 
 390 
 265 
 200 
 112 
 
 1190 
 565 
 370 
 260 
 168 
 
 1770 
 855 
 370 
 412 
 
 265 
 
 Machinists do not, as a rule, consult a table for drill speeds be- 
 cause the hardness of the material varies, and drilling machines are 
 not usually calibrated for the spindle speeds. It will therefore re- 
 quire some practical experience before a beginner can properly 
 determine the speeds for different sizes of drills. 
 
 Centering the Drill. There are two common methods used for 
 centering the drill in piece A. In either case the center punch mark 
 must be enlarged to about 1/16 inch in diameter. 
 
 The first method is to drill a small hole about 1/8 inch in diam- 
 eter and 3/16 deep. This hole acts as a guide for the 1/2" drill 
 and insures its being in the correct position. 
 
 In the second method a 1/2" drill is used to make a countersink 
 in the work about 1/4" in diameter. If this countersink is not in 
 the center of the circle, chip a small groove on the side that is 
 farthest from it, as in Fig. 43, with a round nose chisel or center 
 
ELEMENTARY MACHINE SHOP PRACTICE 35 
 
 gouge. Drill a little deeper and if the countersink still does not 
 center, repeat the operation. 
 
 Fig. 43 
 
 In either method the drill must be centered before it cuts to its 
 full size. 
 
 Laying Off Holes in Piece B. After the holes have been 
 drilled in piece A place it in position on B. With a scriber lay out 
 the circles on B by marking through the holes in A. 
 
 Drilling Piece B. The holes in piece B should be drilled a little 
 larger than the diameter at the bottom of the threads of a 1/2" tap. 
 This is 13/32 of an inch. 
 
 Center punch the center of the circles as accurately as possible 
 by eye. The drill should be centered by the second method de- 
 scribed above. 
 
 Drilling a Fixed Depth. The desired depth of hole may be 
 obtained with the aid of the graduations on the spindle of the drill 
 press. In case the spindle is not calibrated a mark may be made on 
 it with a piece of chalk to indicate when the desired depth has been 
 reached. 
 
 Tapping. Clamp the work in the bench vise and tap the holes, 
 first using a 1/2" plug tap, then a 1/2" bottoming tap. 
 
 The plug tap is started by pressing down on it and turning it 
 with a wrench. After the tap has entered deep enough to cut a full 
 thread, in this case about 5/16" deep, it is no longer necessary to 
 press down on it as the tap will then draw into the work when 
 turned. 
 
 Lard oil should be used for lubrication when tapping cast iron 
 or steel. Brass is usually tapped dry. 
 
 The accuracy with which a hole is tapped depends upon the 
 operator, as the tap will not follow the hole. The tap should there- 
 fore be started square with the face of the work. In some cases 
 
36 
 
 ELEMENTARY MACHINE SHOP PRACTICE 
 
 this may be judged by eye, but it is usually necessary for beginners 
 to use a square or the blade of a square, as in Fig. 44. In this case 
 the blade is placed back of the tap and away from the hole. The 
 tap is squared up by bringing its shank parallel with the edge of 
 the blade. If the blade were placed over the edge of the hole, the 
 small ridge produced by the tap would tip it out of square. The tap 
 must be squared before it cuts to its full diameter as any attempt to 
 straighten it after that is liable to break it. 
 
 \ 
 
 Fig. 44 
 
 As the plug tap is tapered at the end, it will not cut the full size 
 of thread to the bottom of the hole. It is desirable on account of 
 strength to have the length of the full threads greater than the diam- 
 eter of the screw. The tapping should therefore be finished with a 
 bottoming tap which will cut full threads nearly to the bottom of the 
 hole. 
 
 The reason for not using the bottoming tap for the entire tap- 
 ping operation is that it is practically impossible to start such a tap. 
 
 Filing Holes in Piece A. In case the holes in piece B do not 
 match up exactly with those in A, the screws will bind or will not go 
 in at all. It is then necessary to file the holes in A with a round file 
 until the screws no longer bind. 
 
PART III. 
 
 MILLING MACHINE WORK 
 
ELEMENTARY MACHINE SHOP PRACTICE 37 
 
 MILLING MACHINE WORK 
 
 There are several different kinds of milling machines, but the 
 ones most commonly used are the plain miller and the universal 
 miller. Both of these machines have horizontal spindles. The dif- 
 ference between them is that the table of the plain miller can be 
 moved only at fight angles or parallel to the spindle, while the table 
 of the universal miller may be moved at different angles. The prin- 
 cipal advantage of the universal machine occurs in cutting spiral 
 gears, spiral milling cutters, etc. As this class of work will not be 
 treated in this book only the plain milling machines will be con- 
 sidered. 
 
 As in the case of lathes there are several makes of millers, all 
 of which, although varying in efficiency and utility, employ the same 
 fundamental cutting operations. When one has become familiar 
 with the operation of one machine, he should be able to operate 
 other makes of different design with very little difficulty. 
 
 I 
 CONE-DRIVEN PLAIN MILLER 
 
 The plain miller shown in Fig. 45 has a three step cone drive 
 with double back gears. The small pilot wheel, below the name and 
 index plate, together with the two levers on either side of it are 
 used for changing the feed. The double-ended V-shaped lever under 
 the table is for starting and stopping the feed. The hand crank 
 and hand wheels at the right are for the hand feeds and for raising 
 and lowering the table. 
 
 HIGH-POWER PLAIN MILLER 
 
 Fig. 46 shows a plain miller in which the spindle speed changes 
 are obtained by shifting encased gears near the driving pulley. This 
 is done by means of the small pilot wheel and levers on the gear 
 box below the name. The long hand lever at the right of this box 
 operates the clutch for starting and stopping the machine. 
 
38 
 
 ELEMENTARY MACHINE SHOP PRACTICE 
 
 Fig. 45 
 
ELEMENTARY MACHINE SHOP PRACTICE 
 
 39 
 
 Fig. 46 
 
40 
 
 ELEMENTARY MACHINE SHOP PRACTICE 
 
 EXERCISE NO. 8 
 
 Cast Iron 
 
 C T 
 
 Fig. 47 
 
 Sequence of Operations: 
 
 1. Grind off all gates, fins, sand, etc. 
 Clamp in vise and mill side A. 
 Mill sides B and C square with A. 
 Mill side D parallel to A. 
 Mill both ends square with the other sides. 
 
 2. 
 3. 
 
 4. 
 
 5. 
 
 Object of Grinding Rough Casting. The outer surface of cast 
 iron is hard and more or less covered with sand. This would dull 
 milling cutters even more quickly than it would a lathe or planer 
 tool. As milling cutters are expensive and require more time to 
 sharpen, greater care should be taken to protect their cutting edges. 
 It is not necessary, however, to remove all of the scale, but the cast- 
 ing should be thoroughly cleaned. 
 
 Fig. 48 
 Milling Machine Vise. Fig. 48 shows the vise used in the mill- 
 
ELEMENTARY MACHINE SHOP PRACTICE 
 
 41 
 
 ing machine. It has a graduated swivel base so that it can be 
 turned at different angles. 
 
 Clamping the Work. The work is held in the milling machine 
 vise as shown in Fig. 49. It should rest on two parallels that are 
 wide enough to bring the surface to be milled above the level of the 
 vise. In order to get a tighter grip on it, heavy paper should be 
 placed between it and the jaws of the vise. The paper will also 
 protect the jaws from being marred by the rough sides of the 
 casting. 
 
 Fig. 49 
 
 The Cutter. Work of this sort is milled with a common spiral 
 milling cutter. As these cutters are made in different lengths, one 
 should be selected that is a little longer than the widest surface to 
 be cut. 
 
 The Arbor. All milling machine arbors are provided with col- 
 lars, Fig. 49, of different lengths, so that the position of a cutter on 
 them may be varied. These collars slip loosly on over the arbor and 
 when the nut A is tightened clamp the cutter in place. 
 
 If the cutter is mounted near the main bearing of the milling 
 machine spindle, it will work better than if located near the outer 
 end. 
 
 One end of the arbor is tapered and fits into the spindle B. It 
 may be withdrawn by tightening the nut C. The end D is supported 
 by an out port bearing. 
 
 Most arbors are also provided with a keyway so that wlien 
 heavy cuts are to be taken or a large cutter used it may be keyed 
 to the arbor. 
 
 Caution. Beginners are cautioned to be sure that the direction 
 of rotation and speed of the cutter and the direction of the feed are 
 correct before starting a cut. 
 
42 ELEMENTARY MACHINE SHOP PRACTICE 
 
 Direction of Cutter Rotation. Milling cutters are all ground 
 with clearance A, Fig. 50, and if rotated in the wrong direction will 
 not cut. Therefore, before mounting the cutter start the machine 
 and note the direction of rotation of the arbor. If it rotates as indi- 
 cated by the arrow the cutter should be mounted as shown. If the 
 cutter were mounted as in Fig. 51 it would not cut. 
 
 Fig. 50 Fig. 51 
 
 Cutter Speed. The proper cutting or surface speed of a milling 
 cutter made of carbon steel is about 60 to 70 feet per minute when 
 cutting cast iron. Cutting speed is the velocity of a point on the cir- 
 cumference of the cutter. Thus a cutter 21/2 inches in diameter, 
 and turning 90 revolutions per minute, will have a cutting speed of 
 about 60 feet per minute. 
 
 No fixed rule can be given for the proper cutter speed as too 
 much depends on the character of the work, the hardness of the 
 metal, the size of the machines, etc. Machinists determine the 
 proper speeds by the action of the cutting tool and from previous 
 experiences on work similar in character. 
 
 It will be necessary for the instructor to designate the speed of 
 the machine until the student has had sufficient practice to be able 
 to judge fairly well for himself. It is better to run the cutter too 
 slow than too fast, for if it is run too fast it will soon be ruined. 
 
 Direction of Feed. The direction of the feed in relation to the 
 cutter rotation is very important. Fig. 52 shows the correct way. 
 In this case the direction of the feed is opposite to the rotation of the 
 cutter. The wrong way is shown in Fig. 53. If the work were fed 
 in this manner, the cutter would act as a feed roller and draw the 
 work in faster than it would cut. This would break the teeth of the 
 cutter. 
 
 Roughing Cut. The roughing cut on cast iron should always 
 be deep enough to get under the scale ; in this case about 3/32 or 
 1/8 inch deep. Cast iron and brass are milled dry but on steel the 
 cutter works better if lard oil or some other lubricant is used. 
 
ELEMENTARY MACHINE SHOP PRACTICE 
 
 43 
 
 Fig. 52 Fig. 53 
 
 Rate of Feed. As in the case of the cutter speed no fixed rule 
 can be given for the rate of feed. This should be determined by 
 the instructor. It may be stated, however, that .018 of an inch 
 feed per revolution of the cutter should be safe in this case. If a 
 good machine is used and the iron is soft this feed could be in- 
 creased. 
 
 Finishing Cut. The depth of the finishing cut can be anything 
 up to 1/32 of an inch. If more than this is taken off, the surface 
 may not be uniform. The same cutter speed as for roughing can 
 be maintained but the feed should be increased. If a large surface 
 is to be finished and the iron is soft it will pay, in the amount of 
 time saved, to increase both the speed and the feed. 
 
 After side A, Fig. 47, is finished, the sides B and C are milled 
 square with A. D is then milled parallel with A. The method of 
 clamping the work in the vise is practically the same as that used 
 for the shaper work. 
 
 Fig. 54 
 
 Milling the Ends. If, in milling the ends, the block extends 
 so far above the jaws of the vise that the action of the cutter has a 
 tendency to tip it, turn the vise through 90 degrees and clamp it 
 edgewise as shown in Fig. 54. 
 
44 
 
 ELEMENTARY MACHINE SHOP PRACTICE 
 
 EXERCISE NO. 9 
 
 Fig. 55 
 
 Sequence of Operations: 
 
 1. Mill the recess A and the slot B with a 5/8" end mill. 
 
 2. Mill the corners D and E with a side milling cutter. 
 
 3. Mill the grooves in the bottom with a 3/8" milling cutter. 
 
 4. Mill the concave sides with a forming cutter. 
 
 Milling the Recess and Slot. (Exercise No. 8 is to be used 
 for this exercise.) The recess A and the slot B are good examples 
 of the kind of work for which the end mill is particularly adapted. 
 However, this tool is also used for other kinds of work. 
 
 Fig. 56 
 
 The end mill, Fig. 56, has a taper shank and is mounted in the 
 spindle of the milling machine in the same manner as a drill in a 
 drill press. These shanks have either the Morse taper or the Brown 
 and Sharp taper. The Morse standard taper is used for drills as 
 well as for end mills. The taper of the Brown and Sharp standard 
 is less than the Morse standard. For this reason the shanks of 
 end mills used in milling machines usually have the Brown and 
 Sharp taper as they will stay in the spindle better. 
 
ELEMENTARY MACHINE SHOP PRACTICE 
 
 45 
 
 Fig. 57 
 
 Clamping the Work. Lay off the outline of the recess on the 
 surface of the block and clamp it square in the vise as in Fig. 57. 
 Adjust the position of the block until the end of the mill is just 
 touching the surface at one corner of the recess. In order to de- 
 termine when the recess has been cut to the full depth, set the dial 
 on the cross slide to the zero point. This dial is graduated in thou- 
 sandths of an inch. 
 
 Depth of Cut. Force the end of the mill into the surface for 
 about .03 of an inch and feed the work by hand so that the mill will 
 cut just inside of the outline marked. Repeat this operation until 
 the cross-feed dial reads .250 of an inch, the required depth of the 
 recess. 
 
 End mills usually work better with shallow cuts and coarse feeds 
 than with deep cuts and fine feeds. Another reason for taking shal- 
 low cuts in this case is because there are no teeth at the center of 
 the cutting end A, Fig. 56. This makes it hard to force the tool 
 into the metal. 
 
 Speed of Cutter. As this cutter is much smaller in diameter 
 than the spiral mill used in exercise No. 8 the spindle speed may be 
 increased. 
 
 Milling the Slot. The slot is to be milled with the same end 
 mill that was used for cutting the recess. Before starting this cut, 
 remove the work from the vise and drill a 1/2 inch hole as shown at 
 H, Fig. 58. This hole is necessary on account of the center of the 
 end mill having no teeth. 
 
 After reclamping the work in the vise adjust it so that the mill 
 will be at the end of the slot where the hole has been drilled. Feed 
 the cutter through the block, Fig. 59, as far as the cutting edges 
 will permit. It cuts better in this position than at the outer end. 
 
46 
 
 ELEMENTARY MACHINE SHOP PRACTICE 
 
 Fig. 58 
 
 Fig. 59 
 
 Now feed the work horizontally until the cutter reaches the other 
 end of the slot. 
 
 Rate of Feed. If the automatic feed is used it should be very 
 fine. The safest way for beginners is to feed it by hand. If too 
 coarse a feed is used the cutter will break. 
 
 Direction of Feed. When cutting a slot like this where half 
 of the circumference of the mill is in contact with the metal and 
 when using the end of the mill as in cutting the recess, the feed 
 may be in either direction. 
 
 Gang Milling. When two or more cutters are used on one 
 spindle at the same time it is called gang milling. The corners E 
 and D of this exercise may be milled by first cutting one and then 
 the other with a side milling cutter. A simpler method would be to 
 use two cutters, Fig. 60, with the collar I between them so that they 
 will be the proper distance apart. 
 
 Fig. 60 
 
 A third method is to use a cutter between the side mills instead 
 of a collar. If this method is used the surface should not be milled 
 when squaring the block in exercise No. 8. 
 
 Depth of Cut. When using gang cutters the required depth is 
 usually cut at one time. To set the work for the depth shown in 
 Fig. 55, bring the work up under the revolving cutter until it just 
 touches. Then move the work clear of the cutter and raise it 3/16 
 or .187 of an inch, using the graduated dial on the elevating shaft. 
 
ELEMENTARY MACHINE SHOP PRACTICE 47 
 
 Cutting Speed. The speed of the machine for gang cutting is 
 determined by the diameter of the largest cutter. 
 
 Groove Cutting. The two 3/8 inch grooves in this exercise 
 may be cut with one or two keyway cutters. 
 
 The difference between this cutter and the side milling cutter is 
 that it has no cutting edges on the side. It is used principally for 
 cutting grooves like these and for cutting standard keyways in 
 shafts. 
 
 Forming Cutters. Cutters having curved or irregular cutting 
 edges are usually called formed cutters. The one used for the con- 
 cave surface in this exercise might be classed as such, but is usually 
 called a convex cutter. 
 
 When cutting the concave surface in the end of the block it will 
 be less liable to slip if clamped edgewise in the vise. 
 
48 
 
 ELEMENTARY MACHINE SHOP PRACTICE 
 
 DIVIDING HEAD AND TAILSTOCK 
 
 Fig. 61 
 
 Fig. 61 shows a dividing head and tailstock. The tailstock is 
 used for holding the ends of shafts, mandrels, etc. The small jack 
 shown is for supporting the middle of long slender work when 
 mounted between the centers. 
 
 The Dividing Head. The dividing head is used for accurately 
 spacing or dividing the circumference of a piece of work into any 
 number of parts, as in squaring a shaft, gear cutting, etc. 
 
 The center and slotted arm are made in one piece and like a lathe 
 center are held in the spindle of the dividing head by a taper fit. 
 The slot in the arm is to receive the tail of a lathe dog so that work 
 mounted between the centers will rotate with the spindle of the 
 dividing head. The set screw at the end of the slot is to take up 
 the slack or lost motion between the sides of the slot and the tail 
 of the lathe dog. 
 
 The spindle of the dividing head is threaded like a lathe spindle 
 so that a chuck may be screwed on it. 
 
 The Index Plate. The round plate with a number of circles of 
 holes on the side of the dividing head is called the index plate. 
 
ELEMENTARY MACHINE SHOP PRACTICE 
 
 49 
 
 Index Crank. The index crank is in front of the index plate 
 and is provided with a slot so that by loosening the hexagonal nut 
 at the center it may be moved to different positions. 
 
 Index Pin. At the end of the index crank is the index pin. 
 One end of this pin is of such size that it just fits into the holes in 
 the index plate. The other end has a knurled knob which is used 
 to withdraw the pin so that the crank may be turned. 
 
 Indexing. The shaft on which the index crank is mounted is 
 geared to the spindle of the dividing head at a ratio of 40 to 1. 
 Therefore, 40 turns of the crank will cause the spindle to make one 
 complete revolution. 
 
 If it were desired to make 4 divisions, as in squaring a shaft, the 
 number of turns of the crank would be 40 -=- 4, or 10 revolutions for 
 each cut. To make 40 divisions as in a 40-tooth gear wheel the 
 crank would be turned one revolution for each tooth. 
 
 In case 32 divisions are to be made, the turns of the crank per 
 division would be 40/32 or 1 1/4 revolutions. To turn the crank 
 1/4 of a revolution a circle of holes is selected that is evenly divided 
 by 4 as 24, 36, etc. If the 24 hole circle is used, the crank should be 
 turned 6 holes exclusive of the hole the index pin is in. Therefore 
 to make one of the 32 divisions the index crank is turned 1 revolu- 
 tion plus 6 holes on the 24 hole circle. 
 
 The Sector. All dividing heads are provided with a sector 
 which eliminates counting the holes in the index plate each time a 
 division is made. 
 
 By loosening the screw A, Fig. 62, 
 the arms D and E may be adjusted to in- 
 clude any desired number of holes. Thus 
 to turn the index crank 1/4 of a revolu- 
 tion on a 24 hole circle the index pin 
 should be rotated from B to C. 
 
 Fig. 62 
 
50 
 
 ELEMENTARY MACHINE SHOP PRACTICE 
 
 Fig. 63 
 
 Examples of Use for the Dividing Head. Fig. 63 shows the 
 method of cutting five equally spaced slots on the circumference of a 
 circular plate. The latter is mounted on a mandrel such as is 
 used in cutting gears. The method of supporting the outer end of 
 this mandrel is clearly shown. The cutter used is a side cutting 
 miller. 
 
 An example of accurate indexing is shown in Fig. 64. Thirty-six 
 1/4 inch holes are to be equally spaced on the circumference of a 
 19-inch disc. They are first drilled with a short drill a little under 
 size and are then finished to size with a 1/4-inch end mill. 
 
 This figure also shows the method of handling work larger than 
 the dividing head will swing when the spindle is in the horizontal 
 position. In this case the dividing head spindle has been turned 
 through an angle of 90. 
 
ELEMENTARY MACHINE SHOP PRACTICE 
 
 51 
 
 Fig. 64 
 
52 ELEMENTARY MACHINE SHOP PRACTICE 
 
 SPUR GEARS AND RACK 
 
 Gears whose tooth elements are parallel with their axis are 
 known as spur gears. They are also called straight faced gears. 
 
 There are several different systems of gear teeth outlines, but 
 the one most commonly used is the involute system. This system 
 requires only eight cutters for each pitch and has a wide application. 
 
 The operator of a milling machine should become familiar with 
 the following terms : the pitch circle, the pitch diameter, the circular 
 pitch and the diametral pitch. 
 
 Pitch Circle. The size of a gear is determined by the pitch 
 circle, C, Fig. 65. 
 
 Rack 
 
 Fig. 65 
 
 Pitch Diameter. The pitch diameter is the diameter of the 
 pitch circle, D, Fig. 65. 
 
 Circular Pitch. The circular pitch is the distance from the 
 center of one tooth to the center of the adjoining tooth measured on 
 the pitch circle, B, Fig. 65. 
 
 Diametral Pitch. The diametral pitch is the number of teeth 
 per inch of pitch diameter. It therefore determines the size of the 
 teeth. 
 
 For example, a gear with 12 teeth and a pitch diameter of 2 
 inches will have a diametral pitch of 6. One with 16 teeth and the 
 same pitch diameter will have a diametral pitch of 8. Of these two 
 gears the teeth on the 16 tooth gear will necessarily be smaller than 
 those on the 12 tooth gear. 
 
ELEMENTARY MACHINE SHOP PRACTICE 53 
 
 The distance A, Fig. 65, is the reciprocal of the diametral pitch. 
 Thus on an 8 diametral pitch gear, the distance A is 1/8 of an inch. 
 The diametral pitch will hereafter be referred to as the pitch. 
 
 Shape of Tooth. The thickness of the tooth on the pitch circle 
 is the same in all sizes of gears having the same pitch. The shape 
 of the tooth, however, varies with the size of the gear ; that is, the 
 curve on the side of a tooth on a 12 tooth gear is a little different 
 from that on a gear having 13 teeth. The greatest contrast is noted 
 between a 12 tooth gear and a rack, Fig. 65. 
 
 When gear wheels are cut in a milling machine a formed cutter 
 having the same profile as the space between the teeth is used. If 
 it were necessary to cut the teeth theoretically correct, a different 
 cutter would be required for each different size gear. In practice, 
 however, for the involute system only 8 cutters are used for each 
 pitch. The following table gives the range of each cutter. 
 
 No. 1 will cut wheels from 135 teeth to a rack. 
 
 " 2 " " " " 55 " 134 teeth, inclusive. 
 
 " 3 " " " " 35 " 54 " 
 
 tt ^ it ft ft tt 25 " 34 " " 
 
 ft c tt a a tt 21 " oz ft ft 
 
 ft z ft ft ft ft 17 ft orv tt ft 
 
 tf *J ft ft tt tt -t A ft \ (~\ (< <( 
 
 ft O ft ft ft ft 1 O ft 1-5 If tt 
 
 For example, if it is desired to cut a 10 pitch gear with 28 teeth, 
 a 10 pitch, number 4 cutter should be used. 
 
 Rack. The teeth of a rack are developed along a straight line 
 and mesh with a gear having the same pitch. 
 
54 
 
 ELEMENTARY MACHINE SHOP PRACTICE 
 
 EXERCISE NO. 10 
 
 10 
 
 2. 
 3. 
 
 4. 
 
 5. 
 
 25 T. 12 P. j-f'H 
 Fig. 66 
 
 GEAR CUTTING 
 Sequence of Operations: 
 
 1. Select cutter and mount on milling machine arbor. 
 
 Line up center of cutter with center of the dividing head. 
 
 Place gear blank on mandrel and mount mandrel between 
 
 centers of the dividing head and the tail stock. 
 
 Set cutter to proper depth. 
 
 Set the index crank and sector on dividing head for 25 
 
 divisions. 
 
 Selecting Cutter. The number of teeth to be cut in this gear is 
 25. Referring to the table on page 53 it is seen that a number 5 
 cutter has the proper range. 
 
 Mounting Cutter. The cutter is mounted on the milling ma- 
 chine arbor as close to the main bearing of the spindle as possible 
 and yet far enough away to have it line up with the center of the 
 dividing head. 
 
 Centering Cutter. In order to cut the teeth radially the center 
 of the cutter must be in line with the center of the dividing head. 
 All gear cutters are marked with a center line so that by moving the 
 dividing head close to the cutter and adjusting the position of the 
 table they may be accurately centered. 
 
 Placing Gear on Mandrel. Gear blanks are usually mounted 
 on a gear mandrel, Fig. 67. 
 
 Fig. 67 
 
ELEMENTARY MACHINE SHOP PRACTICE 55 
 
 This mandrel is not tapered, the clamping being done by means 
 of the nut A. By removing the collars B B several gears can be 
 mounted at one time. 
 
 Mounting the Gear Mandrel. A milling machine dog or a 
 lathe dog is fastened on one end of the mandrel. The latter is then 
 mounted between the dividing head center and the tail stock center 
 in very much the same manner as is shown in Fig. 63. Oil should be 
 used on the tail stock center. The set screw in the slotted arm of the 
 dividing head is screwed against the tail of the dog to prevenr any 
 lost motion. 
 
 Depth of Cut. When cutting gear teeth of this size all of the 
 stock is removed at one cut. For gears with large teeth, say of 4 
 or 5 pitch and larger, it may be necessary to take two cuts. 
 
 To set the work so that the cutter will cut the proper depth start 
 the machine and raise the work up under the revolving cutter until 
 it just touches. Move the work clear of the cutter and set the dial 
 on the elevating shaft to zero. Now raise the table .180 of an inch 
 as indicated by the graduations on the dial. This is the proper 
 depth for a 12 pitch gear tooth. 
 
 All milling machines are provided with a chart that gives the 
 depth to be cut and the range of the cutters for all sizes of gears. 
 This side of each cutter is also marked with this information for its 
 particular pitch and range. 
 
 Setting the Index Crank. There is a clamping nut on the side 
 of the dividing head opposite the index plate which should al- 
 ways be loosened before turning the index crank and tightened 
 after indexing. In order to index 25 teeth, the crank must be turned 
 1/25 of 40, or 1 3/5 turns per tooth. 3/5 of a revolution can be 
 measured on a circle of holes which is a multiple of 5 as 20, 25, 30, 
 35, etc. Assuming the use of the 30 hole circle, 3/5 of a revolution 
 will be represented by 18 spaces. 
 
 Loosen the nut B, Fig. 68, and adjust the index pin C in one of 
 the holes of the 30 hole circle. Now tighten the nut B just enough 
 to hold the crank in position and pull out the index pin to see if it 
 will drop into the hole without binding. If the index pin is not in 
 line with the hole its position may be changed slightly by rapping 
 the end of the index crank with a piece of wood. If a light rap is 
 not sufficient loosen the nut a little. After the index pin is properly 
 set, tighten the nut B so that it will stay in this position. 
 
56 
 
 ELEMENTARY MACHINE SHOP PRACTICE 
 
 Fig. 68 
 
 Setting the Sector. Loosen the clamping screw A on the sector, 
 Fig. 68, and move the arm D so that the beveled edge rests against 
 index pin C. Withdraw the index pin and turn the crank to the 
 right 18 holes, not counting the hole the pin was in. Without 
 changing the position of the arm D move the other arm E until its 
 beveled edge strikes the index pin in its new position at the 18th 
 hole. Tighten the screw A. The sector is now set to include 3/5 
 of a turn, or 18 spaces. 
 
 Indexing. Before taking the first cut, turn the index crank 
 clockwise one complete revolution. This will take out all the slack 
 or lost motion in the dividing head. 
 
 To index the gear for the next cut rotate the sector arm D up 
 to the index pin. Withdraw the pin and give the crank one turn to 
 the right or clockwise, plus the fraction of a turn included between 
 the sector arms. This operation is repeated until the gear is finished. 
 
 Cutting a Rack. The size of the teeth of a rack, as with spur 
 gears, is designated by the pitch. 
 
 Fig. 69 
 
f ELEMENTARY MACHINE SHOP PRACTICE 57 
 
 To space the teeth it is necessary to know the distance from the 
 center of one tooth to the center of the adjoining one. For a 12 
 pitch rack this is the same as the circular pitch of 12 pitch spur 
 gears. The circular pitch is obtained by dividing 3.1416 by the 
 diametral pitch. With a diametral pitch of 12 the circular pitch is 
 .262". The following table gives the diametral pitches commonly 
 used and the corresponding circular pitches. 
 
 Diametral Circular Diametral Circular 
 
 Pitch Pitch Pitch Pitch 
 
 \}/ 4 2.5133" 10 .314 
 
 1% 2.0944 11 .286 
 
 1# 17952 12 .262 
 
 2 1.571 14 .224 
 2y 4 1.396 16 .196 
 2% 1.257 18 .175 
 2y 4 1.142 20 .157 
 
 3 1.047 22 .143 
 3i/j .898 24 .131 
 
 4 .785 26 .121 
 
 5 .628 28 .112 
 
 6 .524 30 .105 
 
 7 .449 32 .098 
 
 8 .393 36 .087 
 
 9 .349 40 .079 
 
 48 .065 
 
 Clamp the rack blank in the milling machine vise on a parallel 
 as shown in Fig. 69. After taking the first cut of the required depth, 
 set the dial on the cross feed to zero. Move the table horizontally 
 .262" as indicated by the dial on the hand crank. Take another cut 
 and continue this operation until the rack is finished. If one end of 
 the rack, as A, extends beyond the vise, it will be necessary to reset 
 the work as the cutter will not cut satisfactorily with such poor 
 support. 
 
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