An interesting example of flat turret lathe work is shown in Fig. 22.
This is a steel sh.e.l.l 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 sh.e.l.ls 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 sh.e.l.l is severed.
[Ill.u.s.tration: Fig. 23. First Operation on Sh.e.l.l Ill.u.s.trated in Fig.
22--Rough-turning and Boring]
In finishing this sh.e.l.l, five different operations are required. During the first operation the sh.e.l.l is rough-bored and turned by one pa.s.sage 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 sh.e.l.l.
[Ill.u.s.tration: Fig. 24. Second Operation--Cutting Internal Thread]
One of the interesting features connected with the machining of this sh.e.l.l 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.
[Ill.u.s.tration: Fig. 25. Third Operation--Turning Recess at Rear End; Tool is shown withdrawn]
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 sh.e.l.l wall, caused by the threading operation.
[Ill.u.s.tration: Fig. 26. Fourth Operation--Finishing the Bore and Outside]
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.
[Ill.u.s.tration: Fig. 27. Fifth Operation--Rounding Ends, Scoring Large End, and Cutting Off]
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 sh.e.l.l 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 sh.e.l.l 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 f.l.a.n.g.e 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 f.l.a.n.g.e 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.
[Ill.u.s.tration: Fig. 28. Tool Equipment for Turning Scroll Gear Blank on Acme Flat Turret Lathe]
After roughing the f.l.a.n.g.e, the turret carriage is locked or clamped rigidly to the bed to prevent any lengthwise movement, and the back face of the front f.l.a.n.g.e 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 k.n.o.b at the front of the slide) and the cylindrical hub is turned back to the rear f.l.a.n.g.e, the feed being disengaged by the auxiliary stop just as the tool reaches the f.l.a.n.g.e. 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 f.l.a.n.g.es 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 f.l.a.n.g.es 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_.
[Ill.u.s.tration: Fig. 29. Acme Flat Turret Lathe Arranged for Turning Roller Feed Body]
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_.
[Ill.u.s.tration: Fig. 30. Turret and Head of Jones & Lamson Double-spindle Flat Turret Lathe]
=Double-spindle Flat Turret Lathe.=--The extent to which modern turning machines have been developed, especially for turning duplicate parts in quant.i.ty, is ill.u.s.trated 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 quant.i.ties that the time for setting up the machine becomes a secondary consideration.
[Ill.u.s.tration: Fig. 31. Diagram showing Tool Equipment and Successive Steps in Machining Sprocket Blanks on Double-spindle Flat Turret Lathe]
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 ill.u.s.trated 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 ill.u.s.trated), the inside is rough-bored by tools _A_. At the second position of the turret, tools _B_ rough-face the inner sides of the f.l.a.n.g.es; tools _C_ face the outer sides of the f.l.a.n.g.es, while tools _D_ turn the faces of the f.l.a.n.g.es. At the third position of the turret, tools _E_ finish-turn the inside of the f.l.a.n.g.es; tools _F_ finish-turn the outside of the f.l.a.n.g.es, while tools _G_ finish the faces of the f.l.a.n.g.es. At the fourth position of the turret, tools _H_ finish-bore the sprockets; tools _I_ complete the turning on the outside of the f.l.a.n.g.es, while tools _J_ accurately size the interior of the f.l.a.n.g.es.
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.
[Ill.u.s.tration: Fig. 32. Potter & Johnston Automatic Chucking and Turning Machine]
=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.
[Ill.u.s.tration: Fig. 33. Rear View of Machine showing the Cross-slide Mechanism, Driving Gearing, etc.]
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.
[Ill.u.s.tration: Fig. 34. The Automatic Controlling Mechanism for Feeds and Speeds]
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 ill.u.s.trating 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 ill.u.s.trate 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 (ill.u.s.trated 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.
[Ill.u.s.tration: Fig. 35. Simple Example of Work done in Automatic Chucking and Turning Machine]
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 f.l.a.n.g.e, 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.
[Ill.u.s.tration: Fig. 36. Front View of Machine set up for the Finishing Operation on the Recessed Bushing and Collar shown in the Foreground and in Fig. 35]
=Determining Speed and Feed Changes.=--As previously mentioned, the particular machine ill.u.s.trated 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. a.s.suming 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.
[Ill.u.s.tration: Fig. 37. Plate on the Headstock of Machine Ill.u.s.trated in Fig. 32 giving the Speeds and Feeds]
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 coa.r.s.e 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 coa.r.s.e 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 pa.s.ses 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 f.l.a.n.g.e 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 f.l.a.n.g.e is turned, the cam-drum being fed by hand. This is the first trial cut on the piece.