Part 12 (1/2)
=General Description of a Turret Lathe.=--The turret lathe shown in Fig.
1 has a hexagonal shaped turret _A_ with a hole in each side in which the tools are held. This turret is mounted on a slide _B_ which is carried by a saddle _C_ that can be moved along the bed to locate the turret slide with reference to the length of the tools in the turret and the room required for indexing. The turret slide can be moved longitudinally by turning the pilot wheel or turnstile _D_, or it can be fed by power. Ordinarily, the hand adjustment is used for quickly moving the carriage when the tools are not cutting, although sometimes the hand feed is preferable to a power feed when the tools are at work, especially if the cuts are short. After a turret tool has finished its cut, the turnstile is used to return the slide to the starting point, and at the end of this backward movement the turret is automatically indexed or turned one-sixth of a revolution, thus bringing the next tool into the working position. The turret is accurately located in each of its six positions by a lock bolt which engages notches formed in a large index ring at the turret base. A binder lever _E_ at the top of the turret stud is used to clamp the turret rigidly to the slide when the tools are cutting.
The forward movement of the slide for each position of the turret is controlled by stops at _F_, which are set to suit the work being turned.
When parts are being turned from bar stock, the latter pa.s.ses through the hollow spindle of the headstock and extends just far enough beyond the end of the spindle to permit turning one of the parts. The bar is held while the turning tools are at work, by a chuck of the collet type at _G_. This chuck is opened or closed around the bar by turning handwheel _H_. After a finished part has been cut off by a tool held in cross-slide _J_, the chuck is released and further movement of wheel _H_ causes ratchet feed dog _K_, and the bar which pa.s.ses through it, to be drawn forward. This forward movement is continued until the end of the bar comes against a stop gage held in one of the turret holes, to insure feeding the bar out just the right amount for turning the next piece. On some turret lathes, the lever which operates the chuck also controls a power feed for the bar stock, the latter being pushed through the spindle against the stop.
The machine ill.u.s.trated has a power feed for the cross-slide as well as for the turret. The motion is obtained from the same shaft _L_ which actuates the turret slide, but the feed changes are independent. The cross-slide feed changes are varied by levers _M_ and those for the turret by levers _N_. For many turret lathe operations, such as turning castings, etc., a jawed chuck is screwed onto the spindle and the work is held the same as when a chuck is used on an engine lathe. Sometimes chucks are used having special jaws for holding castings of irregular shape, or special work-holding fixtures which are bolted to the faceplate. The small handle at _O_ is for moving the cross-slide along the bed when this is necessary in order to feed a tool sidewise.
This particular machine is driven by a motor at the rear of the headstock, connection being made with the spindle through gearing. The necessary speed changes are obtained both by varying the speed of the motor and by s.h.i.+fting gears in the headstock. The motor is controlled by the turnstile _P_ and the gears are s.h.i.+fted by the vertical levers shown.
While many of the features referred to are common to turret lathes in general, it will be understood that the details such as the control levers, arrangement of stops, etc., vary on turret lathes of different make.
[Ill.u.s.tration: Figs. 2 and 3. Diagrams showing Turret Lathe Tool Equipment for Machining Automobile Hub Casting]
=Example of Turret Lathe Work.=--The diagrams Figs. 2 and 3 show a turret lathe operation which is typical in many respects. The part to be turned is a hub casting for an automobile and it is machined in two series of operations. The first series is shown by the plan view, Fig.
2. The casting _A_ is held in a three-jaw chuck _B_. Tool No. 1 on the cross-slide is equipped with two cutters and rough faces the f.l.a.n.g.e and end, while the inner and outer surfaces of the cylindrical part are rough bored and turned by combination boring and turning tool No. 2.
This tool has, in addition to a regular boring-bar, a bracket or tool-holder which projects above the work and carries cutters that operate on the top surface. Tools Nos. 3 and 4 next come into action, No. 3 finis.h.i.+ng the surfaces roughed out by No. 2, and No. 4 finish-facing the f.l.a.n.g.e and end of the hub. The detailed side view of Tool No. 3 (which is practically the same as No. 2), shows the arrangement of the cutters _C_ and _D_, one of which turns the cylindrical surface and the other bevels the end of the hub. The hole in the hub is next finished by tool No. 5 which is a stepped reamer that machines the bore and counterbore to the required size within very close limits. The surfaces machined by the different tools referred to are indicated by the sectional view _E_ of the hub, which shows by the numbers what tools are used on each surface.
For the second series of operations, the position of the hub is reversed and it is held in a spring or collet type of chuck as shown by the plan view Fig. 3. The finished cylindrical end of the hub is inserted in the split collet _F_ which is drawn back into the tapering collet ring by rod _G_ (operated by turnstile _H_, Fig. 1) thus closing the collet tightly around the casting. The first operation is that of facing the side of the f.l.a.n.g.e and end of the hub with tool No. 6 on the cross-slide, which is shown in the working position. A broad cutter _H_ is used for facing the f.l.a.n.g.e and finis.h.i.+ng the large fillet, and the end is faced by a smaller cutter _I_. When these tools are withdrawn, tool No. 7 is moved up for rough turning the outside of the cylindrical end (preparatory to cutting a thread) and rough boring the hole. These same surfaces are then finished by tool No. 8. The arrangement of tools Nos. 7 and 8 is shown by the detailed view. Tool _J_ turns the part to be threaded; tool _K_ turns the end beyond the threaded part; and tool _L_ bevels the corner or edge. The reaming tool No. 9 is next indexed to the working position for finis.h.i.+ng the hole and beveling the outer edge slightly. At the same time, the form tool No. 10, held at the rear of the cross-slide, is fed up for beveling the f.l.a.n.g.e to an angle of 60 degrees. The final operation is that of threading the end, which is done with die No. 11. The boring-bars of tools Nos. 2, 3, 7 and 8 are all provided with pilots _N_ which enter close fitting bus.h.i.+ngs held in the spindle, to steady the bar while taking the cut. This is a common method of supporting turret lathe tools.
The feed of the turret for both the first and second series of operations is 1/27 inch per revolution and the speeds 60 revolutions per minute for the roughing cuts and 90 revolutions per minute for the finis.h.i.+ng cuts. The total time for machining one of these castings complete is about 7-1/2 minutes, which includes the time required for placing the work in the chuck.
=Machining Flywheels in Turret Lathe.=--Figs. 4 to 6, inclusive, ill.u.s.trate how a gasoline engine flywheel is finished all over in two cycles of operations. First the flywheel is turned complete on one side, the hole bored and reamed, and the outside of the rim finished; in the second cycle the other side of the flywheel is completed.
[Ill.u.s.tration: Fig. 4. First Cycle of Operations in Finis.h.i.+ng Gasoline Engine Flywheels on a Pond Turret Lathe]
During the first operation, the work is held by the inside of the rim by means of a four-jaw chuck equipped with hard jaws. The side of the rim, the tapering circ.u.mference of the recess, the web, and the hub are first rough-turned, using tools held in the carriage toolpost. The hole is then rough-bored by bar _C_, which is supported in a bus.h.i.+ng in the chuck, as shown in Fig. 4. The outside of the wheel rim is rough-turned at the same time by a cutter held in the extension turret tool-holder _T_ (Fig. 5), and the taper fit on the inside of the flywheel is turned by means of cutter _A_ (Fig. 4) held in a tool-holder attached to the turret.
The outside of the wheel rim is next finish-turned with cutter _V_ (Fig.
5) held in an extension turret tool-holder the same as the roughing tool _T_. At the same time, the bore is finished by a cutter in boring-bar _D_ (Fig. 4). The side of the rim and the hub of the wheel are also finished at this time by two facing cutters _H_ and _K_, held in tool-holders on the face of the turret. When the finis.h.i.+ng cuts on the rim and hub are being taken, the work is supported by a bus.h.i.+ng on the boring-bar which enters the bore of the wheel, the boring cutter and facing tools being set in such relation to each other that the final boring of the hole is completed before the facing cuts are taken.
[Ill.u.s.tration: Fig. 5. Elevation of Turret and Tools for Finis.h.i.+ng Flywheels--First Operation]
The web of the wheel is next finish-faced with the facing cutter held in the holder _E_, and the taper surface on the inside of the rim is finished by the tool _L_, at the same time. While these last operations are performed, the work is supported by a bus.h.i.+ng on a supporting arbor _J_, which enters the bore of the wheel. The bore is finally reamed to size by a reamer _F_ held in a ”floating” reamer-holder. When the reaming operation is completed, a clearance groove _N_ is cut on the inside of the rim, using a tool _G_ held in the carriage toolpost. The first cycle of operations on the flywheel is now completed.
The flywheel is then removed from the chuck, turned around, and held in ”soft” jaws for the second cycle of operations, the jaws fitting the outside of the wheel rim. (Soft unhardened jaws are used to prevent marring the finished surface of the rim.) The operations on this side are very similar to those performed on the other side. First, the side of the rim, the inside of the rim, the web, and hub are rough-turned, using tools held in the carriage toolpost. The inside of the rim and the web are then finished by a cutter held in a tool-holder at _P_, Fig. 6, which is bolted to the face of the turret. The work is supported during this operation by a bus.h.i.+ng held on a supporting arbor _U_, having a pilot which enters a bus.h.i.+ng in the chuck. Finally, the rim and hub are finished, by the facing cutters _R_ and _S_, the work being supported by an arbor, as before.
[Ill.u.s.tration: Fig. 6. Second Cycle of Operations on Flywheel]
These operations ill.u.s.trate the methods employed in automobile factories, and other shops where large numbers of engine flywheels, etc., must be machined.
=Finis.h.i.+ng a Flywheel at One Setting in Turret Lathe.=--The plan view _A_, Fig. 7, shows an arrangement of tools for finis.h.i.+ng a flywheel complete at one setting. The hole for the shaft has to be bored and reamed and the hub faced on both sides. The sides and periphery of the rim also have to be finished and all four corners of the rim rounded.
The tools for doing this work consist of boring-bars, a reamer, facing heads on the main turret, a turret toolpost on the slide rest (carrying, in this case, three tools) and a special supplementary wing rest attached to the front of the carriage at the extreme left.
The casting is held by three special hardened jaws _b_ in a universal chuck. These jaws grip the work on the inner side of the rim, leaving room for a tool to finish the rear face without striking the chuck body or jaws. Three rests _c_ are provided between the chuck jaws. The work is pressed against these rests while being tightened in the chuck, and they serve to locate it so that the arms will run true so far as sidewise movement is concerned. These rests also locate the casting with relation to the stops for the turret and carriage movements. The chuck carries a bus.h.i.+ng _r_ of suitable diameter to support the boring-bars in the main turret, as will be described.
In the first operation, boring-bar _m_ is brought in line with the spindle and is entered in bus.h.i.+ng _r_ in the chuck. Double-ended cutter _n_ is then fed through the hub of the pulley to true up the cored hole.
While boring the hole, the scale on the front face of the rim and hub is removed by tool _j_. Tool _k_ is then brought into action to rough turn the periphery, after which tool _e_, in the wing rest, is fed down to clean up the back face of the rim. As soon as the scale is removed, the hole is bored nearly to size by cutter _n_{1}_ in bar _m_{1}_, and it is finally finished with reamer _q_ mounted on a floating arbor.
The cutters _f_, _g_ and _h_, in the facing head, are next brought up to rough face the hub and rim, and round the corners of the rim on the front side. This operation is all done by broad shaving cuts. The facing head in which the tools are held is provided with a pilot bar _t_ which fits the finished hole in the flywheel hub, and steadies the head during the operation. The cutters _f_, _g_ and _h_ are mounted in holders which may be so adjusted as to bring them to the proper setting for the desired dimensions. This completes the roughing operations.