Turning and Boring Part 13

[Ill.u.s.tration: Fig. 10. Examples of Box-tool Designs]

Sketch _C_ shows the box-tool used for the second operation. As the hub is flush with the rim on the side for which this tool is intended, it needs only one cutter to face both. This is done by the wide cutter _a_ which is held in a dove-tailed slot in the front of the tool and is fastened by the clamp _b_ and collar-screw _c_. The bus.h.i.+ng _d_, in which the end of the work arbor is supported, is held by the collar-screw _e_, and to obtain the necessary compression, the body of the tool is slotted as far back as _f_. This bus.h.i.+ng is provided with oil grooves and one side is cut away to clear the cutter _a_. The pilot end of the arbor on which the work is mounted is 1/16 inch smaller than the bore of the pulley, which allows the cutter to be set in far enough to prevent any burr which might form at the edge of the bore. A disk _i_ is inserted back of bus.h.i.+ng _d_, so that the latter may be easily removed by pa.s.sing a rod through the hollow shank. The special chuck used for this second operation on the loose pulley is screwed onto the spindle, and the work is mounted on a projecting arbor and driven by the pins engaging holes in the pulley web. The arbor is made a driving fit for the work, and the end or pilot is a running fit in the bus.h.i.+ng of the box-tool. A counterbore in the arbor hub provides clearance for the hub of the pulley which projects beyond the rim on one side.

[Ill.u.s.tration: Fig. 11. (A) Hollow Mill and Holder. (B) Spring Screw-threading Die and Releasing Die-holder]

=Hollow Mills.=--A hollow mill such as is shown at _A_ in Fig. 11 is sometimes used in place of a box-tool (especially when turning bra.s.s) for short roughing cuts preceding a threading operation. The turning is done by the cutting edges _e_, and the turned part enters the mill and is steadied by it. If this type of tool is used for long, straight cuts, especially on square stock and when making screws with large heads from the bar, it should always be followed by a finis.h.i.+ng box-tool to insure accurate work. A hollow mill can be sharpened readily by grinding the ends without materially changing the cutting size. A slight adjustment can be obtained by means of the clamp collar shown to the left, although this is not generally used. When making these mills, they should be reamed out tapering from the rear to give clearance to the cutting edges. For turning steel, the cutting edge should be about 1/10 of the diameter ahead of the center, whereas for bra.s.s, it should be on the center-line.

[Ill.u.s.tration: Fig. 12. Geometric Adjustable Hollow Milling Tool]

Hollow mills are also made adjustable. The design shown in Fig. 12 is especially adapted for bra.s.s finis.h.i.+ng. It can also be used for taking light cuts on cast iron or steel but its use in place of roughing or finis.h.i.+ng box-tools for general use is not recommended. With the exception of the cutters and screws, the complete tool consists of three parts, _viz._, the holder, cam, and ring. The cam serves to adjust the cutters for different diameters. The adjustment is made by the two screws shown, the amount being indicated by a micrometer scale. When adjusting the cutters for a given diameter, the use of a hardened steel plug of the required size is advisable, the cutters being adjusted against the plug.

=Releasing Die and Tap Holders.=--Threads are cut in the turret lathe by means of dies for external threading, and taps for internal threading, the die or tap being held in a holder attached to the turret. A simple form of releasing die holder is shown at _B_, Fig. 11. This holder was designed for the spring-screw type of threading die shown to the left.

The die is clamped in the holder _a_ by the set-screw shown, and the shank _b_ of the holder is inserted in the turret hole. Holder _a_ has an extension _c_ which pa.s.ses through the hollow shank. When the die is pressed against the end of the work, holder _a_ and its extension moves back until lug _d_ on the holder engages lug _e_ on the shank. The die and holder are then prevented from rotating with the work and the die begins to cut a thread. It continues to screw itself onto the work with the turret following, until the thread has been cut to the required length; the turret is then stopped and as the die and holder _a_ are drawn forward, lugs _d_ and _e_ disengage so that the die simply rotates with the work without continuing to advance. The lathe spindle is then reversed and as the turret is moved back by hand, pin _f_ comes around and enters notch _g_, thus holding the die stationary; the die then backs off from the threaded end. Some tap holders are also constructed the same as this die holder, so far as the releasing mechanism is concerned. There are also many other designs in use, some of which operate on this same principle.

[Ill.u.s.tration: Fig. 13. Geometric Self-opening and Adjustable Screw-cutting Die Head]

=Self-opening Die Heads.=--The type of die holder shown at _B_ in Fig.

11 is objectionable because of the time required for backing the die off the threaded end; hence, self-opening dies are extensively used in turret lathe work. As the name implies, this type of die, instead of being solid, has several chasers which are opened automatically when the thread has been cut to the required length. The turret can then be returned without reversing the lathe spindle. The dies are opened by simply stopping the travel of the turret slide, the stop-rod for the feed of the turret being adjusted to give the proper amount of travel.

[Ill.u.s.tration: Fig. 14. Geometric Collapsing Tap]

A well-known die head of the self-opening type is shown in Fig. 13. The dies open automatically as soon as the travel of the head is r.e.t.a.r.ded, or they can be opened at any point by simply holding back on the turnstile or lever by which the turret slide is moved. The die is closed again by means of the small handle seen projecting at right-angles from the side of the head. The closing may be done by hand or automatically by s.c.r.e.w.i.n.g a pin into a threaded hole opposite the handle and attaching a small piece of flat steel to the back edge of the turret slide. The latter will then engage the pin as the turret revolves, thus closing the die head. This die head has a roughing and finis.h.i.+ng attachment which is operated by handle _A_. When this handle is moved forward, the dies are adjusted outward 0.01 inch for the roughing cut, whereas returning the handle closes and locks the dies for the finis.h.i.+ng cut. The die head has a micrometer scale which is used when making slight adjustments to compensate for the wear of the chasers or to make either a tight-or a loose-fitting thread.

=Collapsing Taps.=--The collapsing tap shown in Fig. 14 is one of many different designs that are manufactured. They are often used in turret lathe practice in place of solid taps. When using this particular style of collapsing tap, the adjustable gage _A_ is set for the length of thread required. When the tap has been fed to this depth, the gage comes into contact with the end of the work, which causes the chasers to collapse automatically. The tool is then withdrawn, after which the chasers are again expanded and locked in position by the handle seen at the side of the holder. In all threading operations, whether using taps or dies, a suitable lubricant should be used, as a better thread is obtained and there is less wear on the tools. Lard oil is a good lubricant, although cheaper compounds give satisfactory results on many cla.s.ses of work.

=Miscellaneous Turret Lathe Tools.=--The chamfering tool shown at _A_, Fig. 15, is used for pointing the end of a bar before running on a roughing box-tool. This not only finishes the end of the bar but provides an even surface for the box-tool to start on. The cutter is beveled on the end to form a cutting edge and it is held at an angle.

The back-rest consists of a bell-mouthed, hardened tool-steel bus.h.i.+ng which supports the bar while the cut is being taken.

The stop gages _B_ and _C_ are used in the turret to govern the length of stock that is fed through the spindle. When a finished piece has been cut off, the rough bar is fed through the spindle and up against the stop gage, thus locating it for another operation. This gage may be a plain cylindrical piece of hardened steel, as at _B_, or it may have an adjusting screw as at _C_; for special work, different forms or shapes are also required. The stop gages on some machines, instead of being held in the turret, are attached to a swinging arm or bracket that is fastened to the turret slide and is swung up in line with the spindle when the stock is fed forward.

The center drilling tool _D_ is designed to hold a standard combination center drill and reamer. This type of tool is often used when turning parts that must be finished afterwards by grinding, to form a center for the grinding machine. The adjustable turning tool _E_ is used for turning the outside of gear blanks, pulley hubs or the rims of small pulleys. The pilot _a_ enters the finished bore to steady the tool, and cutter _b_ is adjusted to turn to the required diameter.

[Ill.u.s.tration: Fig. 15. Various Types of Tools for the Turret Lathe]

The cutting-off tool-holder _F_ (which is held on the cross-slide of the turret lathe) is usually more convenient than a regular toolpost, as the blade can be set closer to the chuck. The blade is held in an inclined position, as shown, to provide rake for the cutting edge; the inclined blade can also be adjusted vertically, a limited amount, by moving it in or out. The multiple cutting-off tool _G_ holds two or more blades and is used for cutting off several washers, collars, etc., simultaneously.

By changing the distance pieces between the cutters, the latter are s.p.a.ced for work of different widths. The flat drill holder _H_ is used for drilling short holes, and also to form a true "spot" or starting point for other drills.

Knurling tools are shown at _I_ and _J_. The former is intended for knurling short lengths and is sometimes clamped on top of the cut-off tool on the cross-slide, the end being swung back after knurling (as shown by the dotted lines) to prevent interference with the work when the cutting-off tool is in operation. The knurling tool _J_ has a shank and is held in the turret. The two knurls are on opposite sides of the work so that the pressure of knurling is equalized. By adjusting the arms which hold the knurls, the tool can be set for different diameters.

Three styles of drill holders are shown at _K_, _L_ and _M_. Holder _K_ is provided with a split collet (seen to the left) which is tightened on the drill shank by a set-screw in the holder. This holder requires a separate collet for each size drill. The taper shank drill holder _L_ has a standard taper hole into which the shank of the drill is inserted.

The adjustable type of holder _M_ is extensively used, especially on small and medium sized machines when several sizes of drills are necessary. This holder is simply a drill chuck fitted with a special shank. For large drills the plain style of holder _K_ is recommended, and if only a few sizes of drills are required, it is more satisfactory and economical than the adjustable type.

The various types of small turret lathe tools referred to in the foregoing for turning, threading, tapping, knurling, etc., are a few of the many different designs of tools used in turret lathe practice.

Naturally, the tool equipment for each particular job must be changed somewhat to suit the conditions governing each case. The tools referred to, however, represent in a general way, the princ.i.p.al types used in ordinary practice. Some of the more special tools are shown in connection with examples of turret lathe work, which are referred to in the following.

=Turning Gasoline Engine Pistons in Turret Lathe.=--The making of pistons for gas engines, especially in automobile factories, is done on such a large scale that rapid methods of machining them are necessary.

The plan view _A_, Fig. 16, shows the turret lathe tools used in one shop for doing this work. As is often advisable with work done in large quant.i.ties, the rough castings are made with extra projections so arranged as to a.s.sist in holding them. These projections are, of course, removed when the piece is completed. In this case the piston casting _a_ has a ring about 1-1/4 inch long and a little less in diameter than the piston, at the chucking end. The piston is held in suitable chuck jaws _b_ which are tightened against the inside of this ring. The set-screws in these special jaws are then tightened, thus clamping the casting between the points of the screws and the jaws. This method of holding permits the whole exterior of the piston to be turned, since it projects beyond the chuck jaws. This is the object in providing the piston with the projecting ring by which it is held.

[Ill.u.s.tration: Fig. 16. (A) Method of Boring and Turning Pistons in Gisholt Lathe. (B) Special Chuck and Tools for Turning, Boring and Cutting Off Eccentric Piston Rings]

The first operation consists in rough-boring the front end of the piston. The double-ended cutter _n_ is held in boring-bar _m_, which is, in turn, supported by a drill-holder, clamped to one of the faces of the turret. This bar is steadied by a bus.h.i.+ng in the drill support _c_ which is attached to the carriage, and may be swung into or out of the operating position, as required. After this cut is completed, the turret is revolved half way around and the casting is finish-bored in a similar manner, with double-ended cutter _n_{1}_ held in bar _m_{1}_, the drill support being used as in the previous case. The support is then turned back out of the way to allow the turning tools in the turret toolpost to be used.

The outside of the piston is next rough-turned with tool _k_ in the turret toolpost, which is revolved to bring this cutter into action. The toolpost is then turned to the position shown, and the outside is finish-turned by tool _j_, which takes a broad shaving cut. The turret tool-holder is again revolved to bring form tool _l_ into position. This tool cuts the grooves for the piston rings. Suitable positive stops are, of course, provided for both the longitudinal and cross movements of the turret toolpost.

In the second operation, the piston _a_ is reversed and held in soft jaws, which are used in place of the hardened jaws _b_ shown in the ill.u.s.tration. These jaws are bored to the outside diameter of the piston, so that when closed, they hold the work true or concentric with the lathe spindle. In this operation the chucking ring by which the piston was previously held is cut off, and the end of the piston is faced true. If the crank-pin hole is to be finished, a third operation is necessary, a self-centering chuck-plate and boring and reaming tools being used. (These are not shown in the ill.u.s.tration.)

=Turning Piston Rings in Turret Lathe.=--One method of turning piston rings is shown at _B_ in Fig. 16. The piston rings are cut from a cast-iron cylindrical piece which has three lugs _b_ cast on one end and so arranged that they may be held in a three-jawed chuck. This cylindrical casting is about 10 inches long, and when the rings are to have their inside and outside surfaces concentric, the casting is held by the lugs in the regular jaws furnished with the chuck. (The arrangement used for turning and boring eccentric rings, which is that shown in the ill.u.s.tration, will be described later.)

The casting _a_, from which the rings are made, is first rough-bored with double-ended cutter _n_ in boring-bar _m_, after which it is finish-bored with cutter _n_{1}_ in bar _m_{1}_. While taking these cuts, the bars _m_ and _m_{1}_ are supported by their extension ends which enter bus.h.i.+ng _r_ located in the central hole of the chuck. This furnishes a rigid support so that a heavy cut can be taken.

The outside of the casting is next rough-turned with tool _k_, held in the turret toolpost. This toolpost is then revolved to bring tool _j_ into position, by which the outside is turned true to size, a broad shaving chip being taken. The toolpost is again swung around, to bring the cutting-off tool-holder _l_ into position. This holder contains four blades set the proper distance apart to give rings of the desired width.

Each blade, from right to left, is set a little back of the preceding one, so that the rings are cut off one after the other, the outer rings being supported until they are completely severed. After the first four rings are cut off, the carriage is moved ahead to a second stop, and four more rings are severed, this operation being continued until the casting has been entirely cut up into rings.

When the bore of the ring is to be eccentric with the outside, the holding arrangement shown in the ill.u.s.tration is used. The casting a is bolted to a sliding chuck-plate _c_, and the outside is rough-turned with tool _k_ in the toolpost. Finis.h.i.+ng tool _j_ is then brought into action, and the outside diameter is turned accurately to size. Then the sliding chuck-plate _c_, carrying the work, is moved over a distance equal to the eccentricity desired, and the work is bored with cutters _n_ and _n_{1}_ as in the previous case. The turret toolpost is next revolved and the tools _l_ are used for cutting off the rings. The reason for finis.h.i.+ng the outside first is to secure smooth rings in cutting off, as this operation should be done when the work is running concentric with the bore, rather than with the exterior surface.

It will be evident that this method gives a far greater output of rings than is possible by finis.h.i.+ng them in the more primitive way on engine lathes. The faces of the rings may be finished in a second operation if desired, or they may be ground, depending on the method used in the shop where the work is being done, and the accuracy required.

[Ill.u.s.tration: Fig. 17. Turning Gasoline Engine Pistons in Pratt & Whitney Turret Lathe]

=Piston Turning in Pratt and Whitney Turret Lathe.=--A turret lathe equipped with tools for turning, facing and grooving automobile gasoline engine pistons is shown in Fig. 17. The piston is held on an expanding pin chuck which is so constructed that all of the pins are forced outward with equal pressure and automatically conform to any irregularities on the inside of the piston. Tool _A_ rough-turns the outside, and just as this tool completes its cut, a center hole is drilled and reamed in the end of the piston by combination drill and reamer _B_. The turret is then indexed one-half a revolution and a finis.h.i.+ng cut is taken by tool _C_. After the cylindrical body of the piston has been turned, tools held in a special holder _E_ attached to the cut-off slide are used to face the ends of the piston and cut the packing-ring grooves. While the grooves are being cut, the outer end of the piston is supported by center _D_. The center hole in the end also serves to support the piston while being ground to the required diameter in a cylindrical grinding machine. The edge at the open end of the piston may also be faced square and the inner corner beveled by a hook tool mounted on the rear cross-slide, although this is usually done in a separate operation. (This provides a true surface by which to hold this end when grinding.)

[Ill.u.s.tration: Fig. 18. Pratt & Whitney Turret Lathe equipped with Special Attachment for Turning Eccentric Piston Rings]

This ill.u.s.tration (Fig. 17) shows very clearly the stops which automatically disengage the turret feed. A bracket _F_ is bolted to the front of the bed and contains six stop-rods _G_ (one for each position or side of the turret). When one of these stop-rods strikes lever _H_, the feed is disengaged, the stop being adjusted to throw out the feed when the tool has completed its cut. Lever _H_ is automatically aligned with the stop-rods for different sides of the turret by a cam _J_ on the turret base. A roller _K_ bears against this cam and, through the connecting shaft and lever shown, causes lever _H_ to move opposite the stop-rod for whatever turret face is in the working position. Lever _L_ is used for engaging the feed and lever _R_ for disengaging it by hand.

The indexing of the turret at the end of the backward movement of the slide is controlled by stop _M_ against which rod _N_ strikes, thus disengaging the lock bolt so that the turret can turn. This stop _M_ is adjusted along the bed to a position depending upon the length of the turret tools and the distance the turret must move back to allow the tools to clear as they swing around.

[Ill.u.s.tration: Fig. 19. Tool Equipment for Machining Worm Gear Blanks--Davis Turret Lathe]

=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 bus.h.i.+ng 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.

[Ill.u.s.tration: Fig. 20. Turning Bevel Gear Blanks in Davis Turret Lathe--First Operation]

=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 finis.h.i.+ng 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 gas.h.i.+ng and bobbing the worm-wheel teeth) by a formed tool _H_ held on the cross-slide.

[Ill.u.s.tration: Fig. 21. Second Operation on Bevel Gear Blanks]

=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.

[Ill.u.s.tration: Fig. 22. Sectional View of Tapering Mold Sh.e.l.l which is turned in Hartness Flat Turret Lathe, as ill.u.s.trated in Figs. 23 to 27, Inclusive]

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 bus.h.i.+ng 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 finis.h.i.+ng 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.

=Sh.e.l.l 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.