Index Plate showing Position of Control Levers for Cutting Threads of Different PitchFig. 33. Index Plate showing Position of Control Leversfor Cutting Threads of Different Pitch
Fig. 33. Index Plate showing Position of Control Leversfor Cutting Threads of Different Pitch
The position of leverLand knobKfor cutting threads of different pitches is shown by an index plate or table attached to the lathe and arranged as shown inFig. 33. The upper sectionaof this table shows the different numbers of threads to the inch that can be obtained when idler gearIis in the position shown by the diagramA. Sectionbgives the changes whenthe idler gear is moved, as shown atB, and, similarly, sectioncgives the changes for positionCof the idler. The horizontal row of figures from 1 to 8 below the word “stops” represents the eight positions for leverL, which has a platep(Fig. 30) just beneath it with corresponding numbers, and the column to the left shows whether knobKshould be out, in a central position, or in.
In order to find what the position of leverLand knobKshould be for cutting any given number of threads to the inch, find what “stop” number is directly above the number of threads to be cut, which will indicate the location of leverL, and also what position should be occupied by knobK, as shown in the column to the left. For example, suppose the lathe is to be geared for cutting eight threads to the inch. By referring to section a we see that leverLshould be in position 4 and knobKin the center, provided the idler gearIwere in positionA, as it would be ordinarily, because all standard numbers of threads per inch (U. S. standard) from1/4inch up to and including 4 inches in diameter can be cut with the idler gear in that position. As another illustration, suppose we want to cut twenty-eight threads per inch. This is listed in sectionc, which shows that leverLmust be placed in position 3 with knobKpushed in and the idler gear shifted to the left as atC.
The simplicity of this method as compared with the time-consuming operation of removing and changing gears is apparent. The diagramDto the right shows an arrangement of gearing for cutting nineteen threads per inch. A 20-tooth gear is placed on the spindle stud (in place of the regular one having 16 teeth) and one with 95 teeth on the lead-screw, thus driving the latter direct as with ordinary change gears. Of course it will be understood that the arrangement of a quick change-gear mechanism varies somewhat on lathes of different make.
Turret lathes are adapted for turning duplicate parts in quantity. The characteristic feature of a turret lathe is the turret which is mounted upon a carriage and contains the tools which are successively brought into the working position by indexing or rotating the turret. In many instances, all the tools required can be held in the turret, although it is often necessary to use other tools, held on a cross-slide, for cutting off the finished part, facing a radial surface, knurling, or for some other operation. After a turret lathe is equipped with the tools needed for machining a certain part, it produces the finished work much more rapidly than would be possible by using an ordinary engine lathe, principally because each tool is carefully set for turning or boring to whatever size is required and the turret makes it possible to quickly place any tool in the working position. Turret lathes also have systems of stops or gages for controlling the travel of the turret carriage and cross-slide, in order to regulate the depth of a bored hole, the length of a cylindrical part or its diameter; hence, turning machines of this type are much more efficient than ordinary lathes for turning duplicate parts, unless the quantity is small, in which case, the advantage of the turret lathe might be much more than offset by the cost of the special tool equipment and the time required for “setting up” the machine. (See “Selecting Type of Turning Machine.”)
Turret Lathe of Motor-driven Geared-head TypeFig. 1. Bardons & Oliver Turret Lathe of Motor-driven Geared-head Type
Fig. 1. Bardons & Oliver Turret Lathe of Motor-driven Geared-head Type
General Description of a Turret Lathe.—The turret lathe shown inFig. 1has a hexagonal shaped turretAwith a hole in each side in which the tools are held. This turret is mounted on a slideBwhich is carried by a saddleCthat 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 pilotwheel or turnstileD, 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 leverEat 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 atF, which are set to suit the work being turned. When parts are being turned from bar stock, the latter passes 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 atG. This chuck is opened or closed around the bar by turning handwheelH. After a finished part has been cut off by a tool held in cross-slideJ, the chuck is released and further movement of wheelHcauses ratchet feed dogK, and the bar which passes 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 illustrated has a power feed for the cross-slide as well as for the turret. The motion is obtained from the same shaftLwhich actuates the turret slide, but the feed changes are independent. The cross-slide feed changes are varied by leversMand those for the turret by leversN. For manyturret 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 atOis 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 shifting gears in the headstock. The motor is controlled by the turnstilePand the gears are shifted 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.
Diagrams showing Turret Lathe Tool Equipment for Machining Automobile Hub CastingFigs. 2 and 3. Diagrams showing Turret Lathe Tool Equipment for Machining Automobile Hub Casting
Diagrams showing Turret Lathe Tool Equipment for Machining Automobile Hub Casting
Figs. 2 and 3. Diagrams showing Turret Lathe Tool Equipment for Machining Automobile Hub Casting
Example of Turret Lathe Work.—The diagramsFigs. 2and3show 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 castingAis held in a three-jaw chuckB. Tool No. 1 on the cross-slide is equipped with two cutters and rough faces the flange 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 finishing the surfaces roughed out by No. 2, and No. 4 finish-facing the flange 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 cuttersCandD, 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 counterboreto the required size within very close limits. The surfaces machined by the different tools referred to are indicated by the sectional viewEof 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 viewFig. 3. The finished cylindrical end of the hub is inserted in the split colletFwhich is drawn back into the tapering collet ring by rodG(operated by turnstileH,Fig. 1) thus closing the collet tightly around the casting. The first operation is that of facing the side of the flange and end of the hub with tool No. 6 on the cross-slide, which is shown in the working position. A broad cutterHis used for facing the flange and finishing the large fillet, and the end is faced by a smaller cutterI. 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. ToolJturns the part to be threaded; toolKturns the end beyond the threaded part; and toolLbevels the corner or edge. The reaming tool No. 9 is next indexed to the working position for finishing 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 flange 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 pilotsNwhich enter close fitting bushings 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 is1/27inch per revolution and the speeds 60 revolutions per minute for the roughing cuts and 90 revolutions per minute for the finishing cuts. The total time for machining one of these castings complete is about 71/2minutes, which includes the time required for placing the work in the chuck.
First Cycle of Operations in Finishing Gasoline Engine Flywheels on a Pond Turret LatheFig. 4. First Cycle of Operations in Finishing Gasoline EngineFlywheels on a Pond Turret Lathe
First Cycle of Operations in Finishing Gasoline Engine Flywheels on a Pond Turret Lathe
Fig. 4. First Cycle of Operations in Finishing Gasoline EngineFlywheels on a Pond Turret Lathe
Machining Flywheels in Turret Lathe.—Figs. 4to6, inclusive,illustrate 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.
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 circumference 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 barC, which is supported in a bushing in the chuck, as shown inFig. 4.The outside of the wheel rim is rough-turned at the same time by a cutter held in the extension turret tool-holderT(Fig. 5), and the taper fit on the inside of the flywheel is turned by means of cutterA(Fig. 4) held in a tool-holder attached to the turret.
Elevation of Turret and Tools for Finishing Flywheels—First OperationFig. 5. Elevation of Turret and Tools for Finishing Flywheels—First Operation
Elevation of Turret and Tools for Finishing Flywheels—First Operation
Fig. 5. Elevation of Turret and Tools for Finishing Flywheels—First Operation
The outside of the wheel rim is next finish-turned with cutterV(Fig. 5) held in an extension turret tool-holder the same asthe roughing toolT. At the same time, the bore is finished by a cutter in boring-barD(Fig. 4). The side of the rim and the hub of the wheel are also finished at this time by two facing cuttersHandK, held in tool-holders on the face of the turret. When the finishing cuts on the rim and hub are being taken, the work is supported by a bushing 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.
The web of the wheel is next finish-faced with the facing cutter held in the holderE, and the taper surface on the inside of the rim is finished by the toolL, at the same time. While these last operations are performed, the work is supported by a bushing on a supporting arborJ, which enters the bore of the wheel. The bore is finally reamed to size by a reamerFheld in a “floating” reamer-holder. When the reaming operation is completed, a clearance grooveNis cut on the inside of the rim, using a toolGheld in the carriage toolpost. The first cycle of operations on the flywheel is now completed.
Second Cycle of Operations on FlywheelFig. 6. Second Cycle of Operations on Flywheel
Second Cycle of Operations on Flywheel
Fig. 6. Second Cycle of Operations on Flywheel
The flywheel is then removed from the chuck, turned around, and held in “soft” jaws for the second cycle of operations, thejaws 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 atP,Fig. 6, which is bolted to the face of the turret. The work is supported during this operation by a bushing held on a supporting arborU, having a pilot which enters a bushing in the chuck. Finally, the rim and hub are finished, by the facing cuttersRandS, the work being supported by an arbor, as before.
These operations illustrate the methods employed in automobile factories, and other shops where large numbers of engine flywheels, etc., must be machined.
Turret Lathe Tool Equipment for Machining FlywheelsFig. 7. Turret Lathe Tool Equipment for Machining Flywheels
Turret Lathe Tool Equipment for Machining Flywheels
Fig. 7. Turret Lathe Tool Equipment for Machining Flywheels
Finishing a Flywheel at One Setting in Turret Lathe.—The plan viewA,Fig. 7, shows an arrangement of tools for finishing 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 jawsbin 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 restscare 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 bushingrof suitable diameter to support the boring-bars in the main turret, as will be described.
In the first operation, boring-barmis brought in line with the spindle and is entered in bushingrin the chuck. Double-ended cutternis 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 toolj. Toolkis then brought into action to rough turn the periphery, after which toole, 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 cuttern1in barm1, and it is finally finished with reamerqmounted on a floating arbor.
The cuttersf,gandh, 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 bartwhich fits the finished hole in the flywheel hub, and steadies the head during the operation. The cuttersf,gandhare 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.
The periphery of the rim is now finished by cutterlin the turret toolpost which is indexed to the proper position for this operation. The rear face of the rim is finished by the same toolewith which the roughing was done. Tooleis then removedand replaced withdwhich rounds the inner corner of the rim. Tooldis also replaced with a third tool for rounding the outer corner of the rear side. For finishing the front faces of the rim and hub and rounding the corners of the rim, a second facing head, identical with the first one, is employed. This is shown in position in the illustration. Cuttersf1,g1andh1correspond with the cuttersf,gandh, previously referred to, and perform the same operations.
The remaining operation of finishing the back of the hub is effected by cutterp. This cutter is removed from the bar, which is then inserted through the bore; the cutter is then replaced in its slot and the rear end of the hub is faced by feeding the carriage away from the headstock. This completes the operations, the flywheel being finished at one setting.
Finishing a Webbed Flywheel in Two Settings.—The plan viewsBandC,Fig. 7, show the arrangement of tools for finishing a webbed flywheel which has to be machined all over. This, of course, requires two operations. In the first of these (see sketchB) the rough casting is chucked on the inside of the rim with regular inside hard chuck jawsb. The cored hole is first rough bored with cutternattached to the end of boring-barm, and guided by the drill supportdpivoted to the carriage. Next, the boring-barm1is brought into position, the drill support being swung back out of the way. This bar is steadied by its bearing in bushingrin the chuck. Two cutters,n1andn2, are used to roughly shape the hole to the desired taper, the small end being finished to within 0.002 inch of the required diameter. While boring with the barm1, the scale is broken on the web and hub of the casting by the toolkin the turret toolpost. The latter is then shifted to bring the tooljinto position for removing the scale on the periphery of the wheel. Next, the hole is reamed with taper reamerq, the pilot of which is supported by bushingr.
The first of the facing heads is now brought into action. This facing head carries a guidetwhich is steadied in a taper bushingc, driven into the taper hole of the hub for that purpose. The top cutterfturns the periphery, cuttergturns the hub and facesthe web, and cutterhfaces the rim. A fourth cuttereon the under side of the head faces the hub. This casting is now machined approximately to size.
For finishing, similar cutters,e1,f1,g1andh1, in the other facing head are used, the latter being supported by the taper bushingcin the same way. A very light cut is taken for finishing. Toollin the carriage turret is used to round the outer and inner corners of the rim, which completes the work on this face of the casting.
In the second cycle of operations, shown atC, the casting is chucked on the outside with the soft jawsb, which are bored to the exact diameter of the finished rim. The work is further supported and centered by sliding bushingc, which is tapered to fit the finished hole in the hub, and has an accurate bearing in bushingrin the chuck. This bushing is provided with a threaded collar for forcing it into the work and withdrawing it. The scale on the web and the inside and face of the rim is first broken with the toolkin the turret toolpost. These surfaces are then roughed off with cuttersf,gandh, in the facing head. This latter is steadied by a pilottwhich enters the hole in the sliding bushingcon which the work is supported. A light cut is next taken with cuttersf1,g1andh1, in the finishing facing head, which completes the operation.
Tools for Turret Lathes.—The operation of a turret lathe after the tools have been properly arranged is not particularly difficult, but designing and making the tools, determining what order of operations will give the most efficient and accurate results, and setting the tools on the machine, requires both skill and experience. For some classes of work, especially if of a rather complicated nature, many of the tools must be specially designed, although there are certain standard types used on turret lathes which are adapted to general turning operations. Some of the principal types are referred to in the following.
Different Types of Box-tools for Turret LatheFig. 8. Different Types of Box-tools for Turret Lathe
Different Types of Box-tools for Turret Lathe
Fig. 8. Different Types of Box-tools for Turret Lathe
Box-tools.—Tools of this type are used for turning bar stock. There are many different designs, some of which are shown inFigs. 8,9and10. Box-tools are held in the turret and they have back-rests opposite the turning tools, for supportingthe part being turned. The box-tool shown atA,Fig. 8, is for roughing. The cutterais a piece of high-speed steel beveled on the cutting end to produce a keen edge. It takes a shearing tangent cut on top of the bar and the latter is kept from springing away by means of the adjustable, hardened tool-steel back-restb. This tool is considered superior to a hollow mill whenever a fair amount of stock must be removed. If considerable smoothness and accuracy are necessary, the finishing box-tool shown atBshould follow the roughing box tool, but in most cases, especially if the part is to be threaded by a die, a finishing cut is unnecessary.
The finishing box-toolBis also used to follow a hollow mill if special accuracy or smoothness is desired. This tool is only intended for light finishing cuts, the allowances varying from 0.005 inch to 0.015 inch in diameter. The cutters are made of square tool steel of commercial size, and are ground and set to take a scraping end cut. This particular tool has two tool-holders which permit finishing two diameters at once. If a larger number of sizes must be turned, extra tool-holders can be applied.
The single-cutter box-tool shown atCis bolted directly to the face of the turret instead of being held by a shank in the turret hole, and it is adapted for heavy cuts such as are necessary when turning comparatively large bar stock. The tool-holderaswivels on a stud, thus allowing the cutter to be withdrawn from the work while being returned, which prevents marring the turned surface. The high-speed steel cutter is ground to take a side cut on the end of the bar. The latter is supported by hardened and ground tool-steel rollsbwhich revolve on hardened and ground studs. These rolls are mounted on swinging arms which have a screw adjustment for different diameters. They can also be adjusted parallel to the bar, thus enabling them to be set either in advance of or back of the cutter. The opening in the base allows the stock to pass into the turret when it is not larger than the turret hole.
The box-tool shown atDis similar to the one just described, except that it has two or more cutters and roller back-rests, thus enabling different diameters to be turned simultaneously. The cutters are ground to take a side cut. Ordinarily this gives a satisfactory finish, but if special accuracy and smoothness are desired, two tools should be used, one for roughing and one for finishing, the latter being ground to take a light scraping end cut.
The taper-turning box-tool shown atEis designed for accurately turning tapers on brass or cast-iron parts, when there is a small amount of stock to be removed. The taper is obtained by cross motion imparted to the cutter slide as the turret advances. The taper-turning box-tool shown atF, instead of having a single-point cutter, is provided with a wide cuttera. This toolis designed to turn tapering parts of small or medium diameter, requiring the use of a support which cannot be provided with a straight forming tool and holder mounted on the cut-off slide. The cutter is backed up by the screws shown, which also provide adjustment for different tapers within a limited range. The bar is supported by the three back-rests shown, which also have screw adjustment.
Box-tools and Work for which they are IntendedFig. 9. Box-tools and Work for which they are Intended
Box-tools and Work for which they are Intended
Fig. 9. Box-tools and Work for which they are Intended
Examples of Box-tool Turning.—Box-tools are not only used for cylindrical and taper turning on the end of a bar, but for many other operations.Figs. 9and10show a number of box-tools of different designs, with examples of the work for which each is intended. While these tools are designed for some specific part, they can, of course, with slight modifications be adapted to other work.
A box-tool of the pilot type that is used for finishing, after the surplus stock has been removed by roughing tools, is shown atA,Fig. 9. The work, which is the cone for a ball bearing, is shown ataby the dotted lines and also by the detail view to the right. The pilotbenters the work before either of the cutters begins to operate on its respective surface. The inverted cutterc, which sizes the flange of the cone, is held in position by a clampd, which is forced down by a collar-head screw. The cutter is further secured against a beveled shoulder atgby the set-screwsf, and it is adjusted forward by the screwe. By loosening the screwsfand the collar-head screw, the cutter may be removed for sharpening. The cutterhis adjusted to cut to the proper diameter, by the screwsl, after which the clampkis made level by the screwj. The collar-screwmis then used to secure the tool in place. The cutter is made from drill rod and it is slightly cupped out on the cutting end to give keenness to the cutting edge. The adjusting screwo, which passes through platep, prevents the cutter from backing away from the work. This adjusting screw plate has its screw holes slotted to avoid removing the screws when it becomes necessary to remove the plate and cutter for sharpening. Pilotbis held firmly to the tool body by set-screwr. The holesthrough the shank makes it easy to remove the pilot, in case this is necessary.
A pilot box-tool for finishing another type of ball bearing cone is shown atB. The shape of the work itself is indicated by the dotted linesaand by the detail view. This tool is somewhat similar in its construction to the one just described. The cuttersbandcare inverted and are used to face the flange atdand to turn it to the proper diameter. These cutters are held by the clampfand screwsgand are adjusted forward by the screwh. The cutterj, which operates on top of the stock, rests on a bolster, of the proper angle and is adjusted up or down by the screwsk. The clampl, which binds against this tool, is beveled to correspond with the angle of the tool. This clamp is secured by the collar-screw shown and it is leveled by set-screwss. The adjusting screwpprevents the cutter from slipping back. The holes in the adjusting-screw plate are also slotted in this case so that it will not be necessary to remove any screws when the cutter has to be taken out of the holder.
A box-tool for finishing a treadle-rod cone for a sewing machine is shown atC. This tool is also of the pilot type. The cutters in it operate on opposite sides of the conea. The inverted cutterbsizes the cylindrical part of the cone, while the front cutterdis set at the proper angle to finish the tapered part. The rear cutterbis held in place by the clampgand a collar screw. It is adjusted forward by the screwhin the plateiwhich is held by screws as shown. The pilot is retained by a set-screw, and it is easily removed by inserting a small rod in the holelwhich passes through the shank. The cutterdis held by clampmand is adjusted by screwnwhich passes through a tapped hole in plateo. The screw holes in both the adjusting platesiandoare slotted to facilitate their removal.
Examples of Box-tool DesignsFig. 10. Examples of Box-tool Designs
Examples of Box-tool Designs
Fig. 10. Examples of Box-tool Designs
The box-tool illustrated atA,Fig. 10, is used for finishing the bushing of a double-taper cone bearinga. The cutters are so arranged that they all cut on the center; that is, the cutting edges lie in a horizontal plane. The inverted cutterbat the rear forms the short angular surface, and the cuttercin front forms the long tapering part of the bearing. The large diameter is turned, to size by cutterd. The pilotehas a bearing in the bore nearly equal to the length of the work and it is providedwith oil grooves, as shown. The taper shank of this pilot is tapped for the screwiwhich extends the whole length of the shank and is used to draw the pilot back to its seat. It is not necessary to remove adjusting-screw platekto take out the cutterb, as the latter can be drawn out from the front after the collar-screwmis loosened. The cuttercis removed by taking off the adjusting-screw platesafter loosening the collar-screwn. The cutterdis held in a dove-tailed slot by two headless set-screwsq. It is also backed up by an adjusting screw in the plates. These adjusting screws should all have fine threads, say from 32 to 40 per inch, and be nicely fitted so they will not loosen after being adjusted.
The box-tools shown atBandC,Fig. 10, are for turning the sides of a loose pulley for a sewing machine. This pulley (shown by the dotted lines) is finished in two operations. The box-tool for finishing the side of the pulley on which the hub projects beyond the rim, is shown atB. The inverted cuttera, which faces the end of the hub, is held by a clampc(clearly shown in the end view) from the under side and it has no adjustment. The collar-screwdis tapped into this clamp, which is prevented from getting out of place by the dowel-pinf. The pilotgis made small in the shank, so that toolacan be so placed as to insure the removal of all burrs around the bore of the hub. The pilot is held by a set-screw and it is provided with oil grooves. The cutterjsizes the outside of the hub, and the cutterkfaces the side of the pulley rim. These cutters are both held by the clampland the collar-screwm. No side plates are used on this tool, and the cutters are all easily removed.
SketchCshows 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 cutterawhich is held in a dove-tailed slot in the front of the tool and is fastened by the clampband collar-screwc. The bushingd, in which the end of the work arbor is supported, is held by the collar-screwe, and to obtain the necessary compression, the body of the tool is slotted as far back asf. This bushing is provided with oil grooves and one side is cut awayto clear the cuttera. The pilot end of the arbor on which the work is mounted is1/16inch 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 diskiis inserted back of bushingd, so that the latter may be easily removed by passing 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 bushing 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.
Hollow Mill and Holder, Spring Screw-threading DieFig. 11. (A) Hollow Mill and Holder.(B) Spring Screw-threading Die and Releasing Die-holder
Hollow Mill and Holder, Spring Screw-threading Die
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 atAinFig. 11is sometimes used in place of a box-tool (especially when turning brass) for short roughing cuts preceding a threading operation. The turning is done by the cutting edgese, 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 finishing box-tool to insure accurate work. Ahollow 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 about1/10of the diameter ahead of the center, whereas for brass, it should be on the center-line.
Geometric Adjustable Hollow Milling ToolFig. 12. Geometric Adjustable Hollow Milling Tool
Geometric Adjustable Hollow Milling Tool
Fig. 12. Geometric Adjustable Hollow Milling Tool
Hollow mills are also made adjustable. The design shown inFig. 12is especially adapted for brass finishing. It can also be used for taking light cuts on cast iron or steel but its use in place of roughing or finishing 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 shownatB,Fig. 11. This holder was designed for the spring-screw type of threading die shown to the left. The die is clamped in the holderaby the set-screw shown, and the shankbof the holder is inserted in the turret hole. Holderahas an extensioncwhich passes through the hollow shank. When the die is pressed against the end of the work, holderaand its extension moves back until lugdon the holder engages lugeon 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 holderaare drawn forward, lugsdandedisengage 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, pinfcomes around and enters notchg, 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.