Part 14 (1/2)
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 finis.h.i.+ng 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 finis.h.i.+ng 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 finis.h.i.+ng 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--Finis.h.i.+ng 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 finis.h.i.+ng 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 finis.h.i.+ng 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 s.h.i.+fted 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 finis.h.i.+ng 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 finis.h.i.+ng 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.