Chapter V: Turret Lathe Practice (2)

=Attachment for Turning Piston Rings.=--Fig. 18 shows a special attachment applied to a Pratt & Whitney turret lathe for turning eccentric, gas-engine piston rings. The boring of the ring casting, turning the outside and cutting off the rings, is done simultaneously. The interior of the casting is turned concentric with the lathe spindle by a heavy boring-bar, the end of which is rigidly supported by a bushing in the spindle. The slide which carries the outside turning tool is mounted on a heavy casting which straddles the turret. The outside of the ring casting is turned eccentric to the bore as a result of an in-and-out movement imparted to the tool by a cam on shaft _A_ which is rotated from the lathe spindle through the gearing shown. For each revolution of the work, the tool recedes from the center and advances toward it an amount sufficient to give the required eccentricity. When the turning and boring tools have fed forward about 2 inches, then the cutting-off tools which are held in holder _B_ come into action. The end of each cutting-off tool, from right to left, is set a little farther away from the work than the preceding tool, so that the end rings are always severed first as the tools are fed in by the cross-slide. A number of the completed rings may be seen in the pan of the machine.

=Turning Worm-gear Blanks in Turret Lathe.=--This is a second operation, the hub of worm-gear blank _G_ (Fig. 19) having previously been bored, reamed, and faced on the rear side. The casting is mounted upon a close-fitting arbor attached to a plate bolted to the faceplate of the lathe, and is driven by two pins which engage holes on the rear side. The rim is first rough-turned by a tool _A_ which operates on top, and the side is rough-faced by a toothed or serrated cutter _B_. A similar tool-holder having a tool _C_ and a smooth cutter _D_ is then used to turn the rim to the required diameter and finish the side. The end of the hub is faced by cutters mounted in the end of bars _E_ and _F_, one being the roughing cutter and the other the finishing cutter. The work arbor projects beyond the hub, as will be seen, and forms a pilot that steadies these cutter bars. The curved rim of the gear is turned to the required radius (preparatory to gashing and bobbing the worm-wheel teeth) by a formed tool _H_ held on the cross-slide.

=Turning Bevel Gear Blanks.=--Fig. 20 shows a plan view of the tools used for the first turning operation on bevel gear blanks (these gears are used for driving drill press spindles). The cored hole is beveled true at the end by flat drill _A_ to form a true starting surface for the three-fluted drill _B_ which follows. The hole is bored close to the required size by a tool (not shown) held in the end of bar _C_, and it is finished by reamer _D_. The cylindrical end of the gear blank or hub is rough-and finish-turned by tools held in holders _E_ and _F_, respectively. (These holders were made to set at an angle of 45 degrees, instead of being directly over the work, as usual, so that the cutters would be in view when setting up the machine.) It will be noted that the chuck is equipped with special jaws which fit the beveled part of the casting.

The second and final operation on this blank is shown in Fig. 21. The work _A_ is held by a special driver plate attached to the faceplate of the machine. This driver plate has two pins which engage holes drilled in the gear blank and prevent it from rotating. The blank is also held by a bolt _B_ which forces a bushing against the cylindrical end. First, the broad beveled side which is to be the toothed part of the gear, is rough-turned by toothed cutters _C_, and a recess is formed in the end of the blank, by a turning tool in this same tool-holder. A similar tool-holder _E_, having finishing cutters, is then used to finish the bevel face and recess. The other tools seen in the turret are not used for this second operation. The rear bevel is roughed and finished by tools and held on the cross-slide.

=Shell Turning Operation in Flat Turret Lathe.=--The "flat turret lathe" is so named because the turret is a flat circular plate mounted on a low carriage to secure direct and rigid support from the lathe bed. The tools, instead of being held by shanks inserted in holes in the turret, are designed so that they can be clamped firmly onto the low circular turret plate.

An interesting example of flat turret lathe work is shown in Fig. 22. This is a steel shell which must be accurately finished to a slight taper, both inside and out, threaded and plain recesses are required at the ends, and, in addition, one or two minor operations are necessary. This work is done in the Hartness flat turret lathe, built by the Jones & Lamson Machine Co. The shells are turned from cold-drawn seamless steel tubing, having a carbon content of 0.20 per cent, and they are finished at the rate of one in nine minutes. The tubing comes to the machine in 12-foot lengths, and the tube being operated upon is, of course, fed forward through the hollow spindle as each successive shell is severed.

In finishing this shell, five different operations are required. During the first operation the shell is rough-bored and turned by one passage of a box-tool, Fig. 23, and the recess _A_, Fig. 22, at the outer end, is finished to size by a second cutter located in the boring-bar close to the turret. The turret is then indexed to the second station which brings the threading attachment _G_ into position, as shown in Fig. 24. After the thread is finished, the recess _B_, Fig. 22, is turned by a flat cutter _K_, Fig. 25. The inner and outer surfaces are then finished to size by a box-tool mounted on the fourth station of the turret and shown in position in Fig. 26. The final operation, Fig. 27, is performed by three tools held on an auxiliary turret cross-slide, and consists in rounding the corners at _b_ and _c_, Fig. 22, and severing the finished shell.

One of the interesting features connected with the machining of this shell is the finishing of the inner and outer tapering surfaces. The taper on the outside is 3/32 inch Per foot, while the bore has a taper of only 1/64 inch per foot, and these surfaces are finished simultaneously. The box-tool employed is of a standard type, with the exception of an inserted boring-bar, and the taper on the outside is obtained by the regular attachment which consists of a templet _D_ (Fig. 23) of the required taper, that causes the turning tool to recede at a uniform rate as it feeds along. To secure the internal taper, the headstock of the machine is swiveled slightly on its transverse ways by the use of tapering gibs. By this simple method, the double taper is finished to the required accuracy without special tools or equipment.

As those familiar with this machine know, the longitudinal movements of the turret as well as the transverse movements of the headstock are controlled by positive stops. The headstock of this machine has ten stops which are mounted in a revolving holder and are brought into position, as required, by manipulating a lever at the front. The stops for length, or those controlling the turret travel, are divided into two general groups, known as "A" and "B". Each of these groups has six stops so that there are two stops for each of the six positions or stations of the turret, and, in addition, five extra stops are available for any one tool, by the engagement of a pin at the rear of the turret. The change from the "A" to the "B" stops is made by adjusting lever _L_, Fig. 26, which also has a neutral position.

After the box-tool for the roughing cut, shown at work in Fig. 23, has reached the end of its travel, further movement is arrested by a stop of the "A" group. The outside turning tool is then withdrawn by operating lever _E_ and the turret is run back and indexed to the second station, thus bringing the threading attachment into position. The surface speed of 130 feet per minute which is used for turning is reduced to about 30 feet per minute for threading by manipulating levers _H_, Fig. 24. After the turret is located by another stop of the "A" group, the threading attachment is made operative by depressing a small plunger _I_, which connects a vertical driving shaft from the spindle with the splined transmission shaft _J_. A reciprocating movement is then imparted to the thread chaser _t_ which advances on the cutting stroke and then automatically retreats to clear the thread on the return. This movement is repeated until the thread is cut to the proper depth, as determined by one of the stops for the headstock. While the thread is being cut, the carriage is locked to the bed by the lever _N_, Fig. 26. It was found necessary to perform the threading operation before taking the outside finishing cut, owing to a slight distortion of the shell wall, caused by the threading operation.

After the thread is finished, the turret is turned to the third station as shown in Fig. 25, and tool _K_ for the inner recess _B_, Fig. 22, is brought into position and fed to the proper depth, as determined by another cross-stop. The turret is also locked in position for this operation. The finishing cuts for the bore and the outside are next taken by a box-tool which is shown near the end of its cut in Fig. 26. This box-tool is similar to the one used for roughing, but it is equipped with differently shaped cutters to obtain the required finish. The outside turning tool has a straight cutting edge set tangent to the cylindrical surface and at an angle, while the boring tool has a cutting edge of large radius. An end view of this box-tool is shown in Fig. 27. A reduced feed is employed for the finishing cut, and the speed is increased to 130 feet per minute, which is the same as that used for roughing.

During the next and final operation, the turret, after being indexed to the position shown in Fig. 27, is first located by a stop of the "A" group so that the cutting-off tool _R_ in front can be used for rounding the corner _b_, Fig. 22. The stop lever _L_ is then shifted and the turret is moved to a second stop of the "B" group. The corner _c_ is then rounded and the shell is scored at _d_ by two inverted tools _S_ and _T_ at the rear, after which the finished work is severed by the cut-off tool at the front. The cross-movement of these three tools is controlled by positive stops on the cross-slide, and the latter is moved to and fro by hand lever _O_. After the shell is cut off, the stop _M_, mounted on the turret, Fig. 26, is swung into position, and the tube is automatically fed forward to the swinging stop by the roll feed, as soon as the chuck is released by operating lever _Q_. This completes the cycle of operations. A copious supply of lubricant is, of course, furnished to the tools during these operations, and the two boring-tool shanks are hollow so that lubricant can be forced through them and be made to play directly upon the cutters.

=Chuck Work in Flat Turret Lathe.=--Two examples of chuck work on the Acme combination flat turret lathe are shown in Figs. 28 and 29. Fig. 28 shows the tool equipment for turning a cylindrical part _A_ which is held in a three-jaw universal chuck. The front flange is first rough-turned by a bent turning tool _B_. The diameter is regulated by one of the cross-stops at _D_ which has been previously set and controls the movement of the turret cross-slide. The longitudinal feed is disengaged when the flange has been turned, by an independent stop. This machine has twelve longitudinal stops, there being one for each turret face and six auxiliary stops, in addition to the stops for the cross-slide.

After roughing the flange, the turret carriage is locked or clamped rigidly to the bed to prevent any lengthwise movement, and the back face of the front flange is rough-turned by tool _B_ in to the diameter of the hub which is indicated by a micrometer dial on the cross-feed screw. The carriage is then unlocked and auxiliary stop No. 7 is engaged (by turning a knob at the front of the slide) and the cylindrical hub is turned back to the rear flange, the feed being disengaged by the auxiliary stop just as the tool reaches the flange. The cross-slide is now moved outward, longitudinal auxiliary stop No. 8 is engaged, the turret slide is moved against the stop, the carriage is locked and the front sides of both the front and rear flanges are rough-faced by tools _B_ and _C_. The turret is next indexed and the hole rough-bored by cutter _E_. After again indexing the turret, the hub and flanges are finish-turned and faced by tools _F_ and _G_, as described for the rough-turning operation. The final operation is that of finishing the bore by cutter _H_.

The operation shown in Fig. 29 is that of turning the body of a roller feed mechanism for a turret lathe. The casting is held in a three-jaw universal chuck and it is first rough-bored by tool _A_. The turret is then indexed and the side of the body and end of the hub are rough-faced by tools at _B_. The turret is again indexed for rough-turning the outside of the hub and body, by tools _C_ and _D_. Similar tools _E_ and _F_ are then used to finish these same surfaces, after which the end of the hub and side of the body are finished by tools _G_ and _H_ similar to those located at _B_. The final operation is that of finishing the bore by tool _J_ and cutting a groove in the outside of the hub by the bent tool _K_.

=Double-spindle Flat Turret Lathe.=--The extent to which modern turning machines have been developed, especially for turning duplicate parts in quantity, is illustrated by the design of turret lathe the turret and head of which is shown in Fig. 30. This machine has two spindles and a large flat turret which holds a double set of tools, so that two duplicate castings or forgings can be turned at the same time. It was designed primarily for chuck work and can be used as a single-spindle machine if desirable. When two spindles are employed for machining two duplicate parts simultaneously, considerably more time is required for setting up the machine than is necessary for the regular single-spindle type, but it is claimed that the increased rate of production obtained with the two-spindle design more than offsets this initial handicap. The manufacturers consider the single-spindle machine the best type for ordinary machine building operations, regardless of whether the work is turned from the bar or is of the chucking variety. On the other hand, the double-spindle type is preferred when work is to be produced in such quantities that the time for setting up the machine becomes a secondary consideration.

When the double-spindle machine is used as a single-spindle type, a chuck 17 inches in diameter is used, and when both spindles are in operation, two 9-inch chucks are employed. The general outline of the turret is square, and the tools are rigidly held, with a minimum amount of overhang, by means of tool-blocks and binding screws connected with the clamping plates. Two duplicate sets of tools are clamped to each side of the turret and these operate simultaneously on the two pieces held in the chucks or on faceplates. Primarily the turret is used in but four positions, but when a 17-inch chuck or faceplate is employed, corner blocks may be held by the clamping plates in which tools are supported, giving, if necessary, four additional operations by indexing the turret to eight positions.

A typical job to demonstrate the application of the double-spindle flat turret lathe is illustrated in Fig. 31. The parts to be turned are sprocket wheels which are held in the two 9-inch chucks. At the first position of the turret (which is the one illustrated), the inside is rough-bored by tools _A_. At the second position of the turret, tools _B_ rough-face the inner sides of the flanges; tools _C_ face the outer sides of the flanges, while tools _D_ turn the faces of the flanges. At the third position of the turret, tools _E_ finish-turn the inside of the flanges; tools _F_ finish-turn the outside of the flanges, while tools _G_ finish the faces of the flanges. At the fourth position of the turret, tools _H_ finish-bore the sprockets; tools _I_ complete the turning on the outside of the flanges, while tools _J_ accurately size the interior of the flanges.

With the double-spindle flat turret lathe, each operation is a double operation, and the speeds are varied according to the nature of the cut; thus, if at one position of the turret, the tools are required to rough out the work, this may be done rapidly, for it has no bearing on the other operations that are subsequently performed. Furthermore, if the following operation has to be performed with great care, this may be done without reducing the speed of the less exacting operations.

=Automatic Chucking and Turning Machine.=--The chucking and turning machine shown in Fig. 32 is automatic in its operation, the feeding of the tools, indexing of the turret, etc., being done automatically after the machine is properly arranged, and the work is placed in the chuck. This machine is adapted to turning and boring a great variety of castings, forgings or parts from bar stock, and it is often used in preference to the hand-operated turret lathe, especially when a great many duplicate parts are required. It is provided with mechanism for operating the cross-slide, feeding the turret slide forward, returning it rapidly, rotating the turret to a new position, and feeding it forward quickly for taking a new cut. The cross-slide and turret-slide movements are effected by cams mounted on the large drum _E_ seen beneath the turret, while the various speed and feed changes are effected by dogs and pins carried on disk _D_ which is keyed to the same shaft that the cam drum is mounted upon. This shaft with the cam drum and governing disk _D_, makes one revolution for each piece of work completed. The cams for operating the turret slide are mounted upon the periphery of drum _E_. The roll which engages the angular faces of these cams and imparts movement to the turret is carried by an intermediate slide which has rack teeth engaging a pinion on the square shaft _C_. By turning this shaft with a crank, the position of the turret-slide, with relation to the cam, may be adjusted for long or short work and long or short tools, as may be required.

The cams which operate the cross-slide are mounted on the right-hand end of drum _E_ and actuate the yoke _A_ (see Fig. 33) which extends diagonally upward. The rear end of this yoke has rack teeth meshing with the teeth of a segmental pinion, which is fastened to rock-shaft _B_. At the headstock end, this rock-shaft carries another segmental pinion meshing with rack teeth formed on the cross-slide. The movement imparted to the yoke by the cams is thus transmitted through the pinions and rock-shaft to the cross-slide.

The cam drum _E_ is driven by a pinion meshing with a gear attached to its front side. This pinion is driven through a train of gearing from pulley _L_ (see Fig. 34) which is belted to the spindle. The feeds are thus always dependent on the spindle speed. By means of epicyclic gearing and suitable clutches, the motion thus derived from the spindle may be made rapid for returning the turret to be indexed and then advancing it to the cutting position again, or very slow for the forward feed when the tools are at work. These changes from slow to fast or _vice versa_ are controlled by disk _D_. This disk carries pins which strike a star wheel located back of the disk at the top, and as this star wheel is turned, the speeds are changed by operation of the gearing and clutches referred to. The first pin _M_ that strikes the star wheel advances it one-sixth of a rotation, changing the feed from fast to slow; the next pin that strikes it advances it another sixth of a rotation, changing the feed from slow to fast and so on. By adjusting the pins for each piece of work, the feed changes are made to take place at the proper time. Handwheel _E_ is geared with the cam-shaft on which the star wheel is mounted, so that the feeds may be changed by hand if desired.

In addition to these feed-changing pins, disk _D_ has a dog which operates a lever by which the feed movement is stopped when the work has been completed. Four rates of feed are provided by quick change gearing of the sliding gear type, operated by handle _K_. With this handle set in the central position, the feed is disengaged. On the periphery of disk _D_ are also clamped dogs or cams _N_, which operate a horizontal swinging lever _P_ connected by a link with vertical lever _J_, which controls the two spindle speeds with which the machine is provided. Either one of these speeds can be automatically engaged at any time, by adjusting the cams _N_ on disk _D_.

Lever _H_ connects or disconnects the driving pulley from the shaft on which it is mounted, thus starting or stopping the machine. The square shaft _G_ serves to operate the drums by hand and is turned with a crank. The rotation of the turret, which takes place at the rear of its travel, is, of course, effected automatically. A dog, which may be seen in Fig. 32 at the side of the bed, is set to trip the turret revolving mechanism at the proper point in the travel, to avoid interference between the tools and the work. The turret is provided with an automatic clamping device. The mechanism first withdraws the locking pin, unclamps the turret, revolves it, then throws in the locking pin and clamps the turret again.

=Example of Work on Automatic Turning Machine.=--The piece selected for illustrating the "setting up" and operation of the automatic chucking and turning machine is shown in Fig. 35. This is a second operation, and a very simple one which will clearly illustrate the principles involved. In the first operation, the hole was drilled, bored and reamed, the small end of the bushing faced, and the outside diameter finished, as indicated by the sketch to the left. (The enlarged diameter at the end was used for holding the work in the chuck.) In the second operation (illustrated to the right), the enlarged chucking end is cut off and, in order to prevent wasting this piece, it is made into a collar for another part of the machine for which the bushing is intended; hence, the outside diameter is turned and the outside end faced, before cutting off the collar. In addition, the bushing is recessed in the second operation, and the outer end faced. In order to have the surfaces finished in the second operation, concentric with those machined in the first operation, the chuck is equipped with a set of soft "false jaws" which have been carefully bored to exactly the diameter of the work to be held.

The first thing to determine when setting up a machine of this type is the order of operations. In this particular case, the order is as follows: At the first position of the turret, the outside collar is rough-turned and the outer end rough-faced. At the second position, the collar is turned to the required diameter and the outer face is finished. The third face of the turret is not equipped with tools, this part of the cycle being taken up in cutting off the collar with a cut-off tool on the rear cross-slide. The fourth operation is that of recessing the bushing, and the fifth operation, facing the end to remove the rough surface left by the cutting-off tool.

The tools _A_ and _B_, Fig. 36, used for turning the outside of the flange, are held in brackets _C_ bolted to the face of the turret. These brackets are each provided with three holes for carrying turning tool-holders. This arrangement provides for turning a number of diameters at different positions, simultaneously, but for this particular operation, a single cutting tool for each tool-holder is all that is necessary. A special device is used for recessing and will be described later.

=Determining Speed and Feed Changes.=--As previously mentioned, the particular machine illustrated in Fig. 32 can be arranged for two automatic changes of speed to suit different diameters on the work. The change gears that will give the required spindle speeds should first be selected. These change gears for different speeds are listed on a speed and feed plate attached to the headstock of the machine (see Fig. 37). It is possible to use one speed from the list given for the fast train of gears, and one from the list for the slow train, so long as the same gears are not used in each case. The diameter of the collar on the work shown in Fig. 35 is 2-1/2 inches, and the diameter of the body is 2 inches. Assuming that the surface speed for this job should be about 40 feet per minute, a little calculation shows that the 66 revolutions per minute, given by the fast train of gears, is equivalent to a surface speed of 43 feet per minute on a diameter of 2-1/2 inches. Moreover, the 78 revolutions per minute obtained from the slow train of gearing, gives about 41 feet per minute on a diameter of 2 inches. The spindle gearing indicated for these speeds is, therefore, placed in position on the proper studs at the back of the machine.

Next we have to determine on which faces of the turret to place the different tools. Each turret face is numbered to agree with the corresponding feed cam on the drum. The speed and feed plate (Fig. 37) gives the various feeds obtainable per revolution of the spindle. As will be seen, the different cams give different feeds. Cam No. 1 has a coarse feed suitable for roughing; cam No. 2 a finer feed adapted to finishing, and so on. Since the first operation consists in rough-turning, cam No. 1 is used. Cam No. 2, which gives a finer feed, is used for the finish-turning operation. Cam No. 4, which is ordinarily used for reaming, could, in this case, be used for recessing, as this recess is for clearance only and may be bored with a coarse feed.

The final operation, which is that of facing, can be done with any cam and cam No. 5 may be used. It will be understood that for facing operations, the feeds given do not apply. As the roll passes over the point of the feed cam at the extreme end of the movement, the feed of the turret slide is gradually slowed down to zero; since the facing takes place in the last eighth or sixteenth inch of this movement, it is done at a feed which is gradually reduced to zero. This is, of course, as it should be, and it is not necessary to pay any attention to the tabulated feeds in facing operations.

=Setting the Turret Slide.=--The next adjustment is that of setting the turret slide. In making this adjustment the turret is set in such relation to the work that the tools will have but a small amount of overhang, the cam-shaft being revolved by hand until the cam-roll is at the extreme top of the forward feeding cam, so that the turret slide is at the extreme of its forward movement. When this adjustment has been made by the means provided, set the turret index tripping dog so as to revolve the turret at the proper point. After a turning tool-holder and tool is attached to the face of the turret, cam No. 1 is placed in its operating position and is revolved by hand until the roll is on the point of the cam and the turret at the forward extreme of its motion. At this point the tool-holder is set so that the cutter will be far enough forward to complete its turning operation. The feed cam is then turned backward, thus returning the turret slide, and the cutter is set to turn the flange to the proper diameter for the roughing cut. The turret slide is fed forward and back while the cutter is adjusted, and when it is properly set, the flange is turned, the cam-drum being fed by hand. This is the first trial cut on the piece.

A facing tool, shown in the working position in Fig. 36, is placed at this station of the turret, being held in the turret hole. This tool has a pilot bar and a holder which contains a facing blade. Feeding by hand, as before, the tool is adjusted lengthwise so as to rough-face the work to the dimension desired. In a similar way the finish-turning and facing tools for the second position of the turret are set, the cam-shaft being revolved by hand to bring this second face and second cam into the working position. (The finish-facing tool is not shown in place in Fig. 36.)

=Setting the Cross-slide Cam.=--As previously mentioned, the third turret face has no tool, the cutting off of the collar being done during this part of the cycle of operations. It has been taken for granted that in setting the turret slide, room has been left between it and the chuck for the cross-slide. The cross-slide is clamped in a longitudinal position on the bed, convenient for the cutting-off operation, which is done with a tool _D_ (Fig. 36) in the rear toolpost, thus leaving the front unobstructed for the operator. When both forming and cutting off are to be done, the forming tool is generally held at the front and the cutting-off tool at the back because heavier and more accurate forming can be done with the work revolving downward toward a tool in the front toolpost, than with the tool at the rear where it is subjected to a lifting action.

The arrangement of the cross-slide cams is shown in Fig. 38, which is an end view of the large drum _E_, Fig. 32. The rear feed cam is the one to be used, and since this cutting-off operation is a short one, it may be done during the return of the turret for position No. 3. The cam drum is, therefore, rotated by hand until the turret face No. 3 has begun to return. The cross-slide cams are then loosened and the rear feed cam is swung around to just touch the roller _R_ which operates arm _A_, the cross-slide having been adjusted out to nearly the limit of its forward travel, leaving approximately enough movement for cutting off the collar. The rear feed cam is then clamped in this position.

A cutting-off tool is next placed in the rear toolpost at the proper height. The rear toolpost slide is then adjusted to bring the point of the cutting-off tool up to the work, and the cam drum is revolved by hand until the piece is cut off. The cross-slide tool is, of course, set in the proper position to make a collar of the required thickness. Feeding by hand is discontinued when the roll is on the point of the cam; the cutting-off tool slide is then permanently set on the cross-slide so that the point of the cutting-off tool enters the bore just far enough to completely sever the collar from the bushing. The motion of the cam drum is continued, by hand, until the roll is over the point of the feed cam. The cross-slide is then pushed back, by hand, until the cam and roll are again in contact, when the return cam is brought up and clamped in position, so that there is just room for the roll between the feed cam and the return cam. The rear return cam (as the hand feed of the cam drum is continued) brings the cross-slide back to its central position. Since there is no front tool used for this series of operations (although a tool is shown in the front toolpost, Fig. 36), the first feed and return cams are allowed to remain wherever they happen to be. These cam adjustments can all be made from the front of the machine.

=Setting the Boring Tool for Recessing.=--The feeding of the turret slide is now continued to make sure that the cutting-off tool is returned to its normal position before the facing tool in the next face of the turret begins to work. The facing of the bushing, so far as the setting of the tool is concerned, is merely a repetition of the facing operation at the first position of the turret. The recessing tool is next set. This tool, which is shown diagrammatically in Fig. 39, is very simple as compared with the somewhat complex operation it has to perform. This recess is for clearance only, and accurate dimensions and fine finish are not necessary. The recessing tool consists simply of a slender boring-bar held in the turret and carrying a cutter suitably located about midway the bar. The forward end of the bar is small enough to enter a bell-mouthed bushing held in the chuck. The boring-bar is bent to one side far enough so that the cutter clears the hole as the bar enters, but is forced into the work as the rounded hole of the bushing engages the end of the bar and deflects it into the working position. The upper diagram shows the position of the bar as it enters the hole, and the lower one the position after it has entered the bushing and is engaged in turning the recess. This bar is set in the turret so that at the extreme forward travel of the turret slide, the recess will be bored to the required length. The cutter must also be adjusted to bore to the desired diameter. This completes the setting of the cutting tools.

=Adjustments for Automatic Feed and Speed Changes.=--The machine must now be set to perform automatically the desired changes of spindle speed and the fast and slow cam movements for the tools. After placing a new piece of work in the machine (the first one having been completed in the setting-up operation), the cam-shaft is revolved by hand until the turning tool in turret face No. 1 is just about to begin its cut. The control wheel _D_, Fig. 34, is rotated in its normal direction until the next graduation marked "slow" is in line with an index mark on the base of the machine. Then the nearest pin _M_ is moved up until it bears against a tooth of the star wheel (previously referred to) and is clamped in this position. The pin should now be in the proper location, but to test its position, rotate the cam shaft backward by hand and throw in the automatic feed; then watch the cut to see if the drum slows down just before the tool begins to work. If it does not, the pin should be adjusted a little, one way or the other, as may be required. (In going over a piece of work for the first time, it is best to have the feed set to the smallest rate, feed change handle _K_ being in position No. 1.)

After the cut has been completed and the turret feed cam-roll is on the high part of the cam, the power feed should again be stopped and the handwheel revolved until the next graduation marked "fast" is opposite the index mark. The next stop pin is then moved up until it just touches the star wheel, where it is clamped in position. The feed being again thrown in, the turret will be returned rapidly, indexed, and moved forward for the second operation. After stopping the automatic movement, the pins are set for this face, and so on for all the operations, including that in which the cross-slide is used for cutting off the finished collar.

As the first, second, and third operations are on comparatively large diameters, they should be done at the slow speed, handle _J_, Fig. 34, being set to give that speed. While the turret slide is being returned between operations 3 and 4, one of the spindle speed-changing dogs _N_ should be clamped to the rim of disk _D_ so as to change the spindle speed to the fast movement. This speed is continued until the last operation is completed, when a second dog is clamped in place to again throw in the slow movement. The feed knock-off dog should also be clamped in place on the disk to stop the machine at the completion of the fifth operation, when the turret is in its rear position. This completes the setting up of the machine. If the feed is finer than is necessary, the feed change handle _K_ may now be moved to a position which will give the maximum feed that can be used.

It has taken considerable time to describe the setting up of the machine for this simple operation, but in the hands of a competent man it can be done quite rapidly. While a simple operation has been referred to in the foregoing, it will be understood that a great variety of work can be done on a machine of this type. It is not unusual to see as many as ten cutting tools operating simultaneously on a piece of work, the tools being carried by the turret, cross-slide and back facing attachment. The latter is operated from a separate cam applied to the cam-shaft and acting through levers on a back facing bar which passes through a hole in the spindle. In this back facing bar may be mounted drills, cutters, facing tools, etc. for machining the rear face of a casting held in the chuck jaws. Where extreme accuracy is required, a double back facing attachment may be used, arranged with cutters for taking both roughing and finishing cuts. The use of this attachment often saves a second operation. This automatic chucking and turning machine is also adapted for bar work, especially in diameters varying from 3 to 6 inches.

=Turning Flywheel in Automatic Chucking and Turning Machine.=--A typical operation on the Potter & Johnston automatic chucking and turning machine is illustrated in Fig. 40, which shows the machine arranged for turning the cast-iron flywheel for the engine of a motor truck. The rim is turned and faced on both sides and the hub is bored, reamed and faced on both sides. The flywheel casting is held in a chuck by three special jaws which grip the inside of the rim. The order of the operations is as follows:

The rear end of the hub is faced by the back facing bar; the cored hole is started by a four-lipped drill in the turret and the front end of the hub is rough-faced. (These tools are on the rear side of the turret when the latter is in the position shown in the illustration.) After the turret indexes, the hole is rough-bored by tool _A_ and while this is being done, the outside of the rim is rough-turned by tool _B_ held in a special bracket attached to the turret. Both sides of the rim are also rough-faced by tools _C_ and _D_ held at the front of the cross-slide, this operation taking place at the same time that the rim is turned and the hole is being bored.

The turret again automatically recedes and indexes, thus locating bar _E_ and turning tool _G_ in the working position. The hole is then finish-bored by tool _E_ and the hub is finish-faced by blade _F_; at the same time the rim is finish-turned by tool _G_ and the sides are finish-faced to the proper width by two tools held at the rear of the cross-slide. The turret automatically recedes and indexes a third time, thus locating the flat-cutter reamer-bar _H_ in the working position and then the hole is reamed to the required diameter. This completes the cycle of operations. The total time for machining this flywheel is forty minutes.

=Automatic Multiple-spindle Chucking Machine.=--An example of the specialized machines now used for producing duplicate parts, is shown in Fig. 41. This is a "New Britain" automatic multiple-spindle chucking machine of the single-head type and it is especially adapted for boring, reaming and facing operations on castings or forgings which can readily be held in chuck jaws. This particular machine has five spindles, which carry and revolve the tools. The work being machined is held stationary in the multiple chuck turret _A_ which holds each part in line with one of the spindles and automatically indexes, so that the work passes from one spindle to another until it is finished. The turret then indexes the finished piece to a sixth or "loading position" which is not opposite a spindle, where the part is removed and replaced with a rough casting. Each pair of chuck jaws is operated independently of the others by the use of a chuck wrench. These jaws are made to suit the shape of the work.

When a single-head machine is in operation, the turret advances and feeds the work against the revolving tools so that a number of pieces are operated upon at the same time. The turret is fed by a cam drum _B_. Cam strips are bolted to the outside of this drum and act directly against a roller attached to the yoke _C_ which can be clamped in different positions on the spindle _D_, the position depending upon the length of the work. On the opposite end of the turret spindle is the indexing mechanism _E_. An automatically spring-operated latch _F_ engages notches in the rim of the dividing wheel, thus accurately locating the turret. The turret is locked by a steadyrest _G_, which, for each working position, automatically slides into engagement with one of the notches in the turret. This relieves the indexing mechanism of all strain.

This type of machine is also built with two spindle heads, the double-head design being used for work requiring operations on both ends. When the double-head machine is in operation, the revolving spindles and tools advance on both sides of the chuck turret, the latter remaining stationary except when indexing. The feed drums on the double-head machine are located directly beneath each group of spindles.

Fig. 42 shows an example of work on a machine of the double-head design. This is an eight-spindle machine, there being two groups of four spindles on each side of the turret. The castings _E_ are for the wheel hubs of automobiles. The order of the operations on one of the castings, as it indexes around, is as follows: The hole in the hub is first rough-reamed by taper reamer _A_ and the opposite end of the hub is rough-faced and counterbored by a tool in spindle _A_{1}_. When the turret indexes, this same casting is reamed close to the finished size by reamer _B_ and the left end of the hub is rough-faced by cutter _F_, while a tool in the opposite spindle _B_{1}_ finishes the counterboring and facing operation. At the third position, reamer _C_ finishes the hole accurately to size, and when the work is indexed to the fourth position, the hub on the left side is finish-faced by a tool in spindle _D_. (The third and fourth spindles of the right-hand group are not used for this particular operation.) When the turret again indexes, the finished casting is removed and replaced with a rough one. While the successive operations on a single casting have just been described, it will be understood that all of the tools operate simultaneously and that a finished casting arrives at the unloading and loading position each time the turret indexes. Three hundred of these malleable castings are machined in nine hours.

=Selecting Type of Turning Machine.=--The variety of machine tools now in use is very extensive, and as different types can often be employed for the same kind of work, the selection of the best and most efficient machine is often a rather difficult problem. To illustrate, there are many different types and designs of turning machines, such as the ordinary engine lathe, the hand-operated turret lathe, the semi-automatic turning machine, and the fully automatic type, which, after it is "set up" and started, is entirely independent. Hence, when a certain part must be turned, the question is, what kind of machine should be used, assuming that it would be possible to employ several different machines? The answer to this question usually depends principally upon the number of parts that must be turned.

For example, a certain casting or forging might be turned in a lathe, which could be finished in some form of automatic or semi-automatic turning machine much more quickly. It does not necessarily follow, however, that the automatic is the best machine to use, because the lathe is designed for general work and the part referred to could doubtless be turned with the regular lathe equipment, whereas the automatic machine would require special tools and it would also need to be carefully adjusted. Therefore, if only a few parts were needed, the lathe might be the best tool to use, but if a large number were required, the automatic or semi-automatic machine would doubtless be preferable, because the saving in time effected by the latter type would more than offset the extra expense for tool equipment and setting the machine. It is also necessary, in connection with some work, to consider the degree of accuracy required, as well as the rate of production, and it is because of these varying conditions that work of the same general class is often done in machines of different types, in order to secure the most efficient results.