Chapter VIII: Special Forms of the Lathe (2)

The method of securing the emery-wheels is shown in Fig. 686. Two flanges Z (made in halves) are let into the wheel, and clamp the wheel by means of the screws shown. The bore of these flanges Z is larger than the diameter of pulleys P, so that the emery-wheels may be changed on the arbor without removing the pulley. Fig. 687 represents an end view of the bearings B for the roll to revolve in, being provided with three pieces, the two side ones of which are adjustable by the set-screws, so as to facilitate setting the roll parallel with the bed of the lathe. The height is adjusted by means of screws K, K, which may also be used in grinding a roll of large diameter at the middle of its length, by occasionally raising the roll as the carriage C proceeds along the roll (the principle of this action is hereafter explained with reference to turning tapers on ordinary lathe work). When the wheels have traversed half the length of the roll, the screws K are operated to lower it again, it being found that the effect of a slight operating of the screws K is so small that the workman's judgment may be relied upon to use them to give to a roll with practical accuracy any required degree of enlarged diameter at the middle of its length with sufficient accuracy for all practical purposes.

There are, however, other advantages of this system, which may be noted as follows. When a single emery-wheel is used there is evidently twice the amount of wear to take a given amount of metal off (per traverse) that there is when two wheels are used, and furthermore the reduction of every wheel diameter per traverse is evidently twice as great with one wheel as it is with two. From some experiments made by Messrs. Morton Poole, it was found that using a pair of 10-inch emery-wheels it would take 40,000 wheel traverses along an average sized calender roll, to reduce its diameter an inch, hence the amount of error due to the reduction of the emery-wheel diameters, per traverse, may be stated as 1/40000 of an inch per traverse, for the two wheels.

Now referring to Fig. 688, let R represent a roll and W W the two emery-wheels.

Suppose the wheels being at the end of a traverse, the roll is 1/40000 inch larger at that end on account of the wear of the emery-wheels, then each wheel will have worn 1/40000 inch diameter or 1/80000 inch radius, hence the increase of roll diameter is equal to the wear of wheel diameter.

Now, suppose that one wheel be used as in Fig. 689, and its reduction of _diameter_ will be equal to that of the two wheels added together, or 1/20000 inch, this would be 1/40000 in the radius of the wheel, producing a difference of 1/20000 difference in the diameter of the wheel.

There is another advantage, however, in that a finer cut can be easier put on in the Poole system, because if a feed be put on of 1/100th inch, the roll is only reduced 1/100th inch in diameter, but if the same amount of feed be put on with a single wheel, it will reduce the roll 1/50th inch, hence for a given amount of feed or movement of emery-wheel towards the roll axis, the amount of cut taken is only half as much as it would be if a single wheel is used. This enables a minimum of feed to be put on the wheel, wear being obviously reduced in proportion as the feed is lighter and the duty therefore diminished.

The method of driving the roll is as follows: Shaft _t_, Fig. 681, runs in bearings in the head, and spindle _r r´_ passes through, and is driven by shaft _t_. A driving pulley is fitted on the spindle at end _r´_, at the other end is a driving chuck _p_ for driving the roll through the medium of a _wabbler_, whose construction will be shown presently. Spindle _r_ may be adjusted endwise in _t_, so that it may be adjusted to suit different lengths of rolls without moving the bearing blocks B.

The wabbler is driven by _p_ and receives the end of the roll to be ground, as shown in Fig. 690, the end of the roll being a taper square and fitting very loosely in a square taper hole in the end of the wabbler; similarly _p_ may have a taper square hole loosely fitting the squared end of the wabbler. The looseness of fit enables the wabbler to drive the roll without putting any strain on it tending to lift or twist it in its bearings in block B, and obviates the necessity for the axis of the rolls to be dead in line with the axis of _r r´_. Various lengths of wabblers may be used to suit the lengths of roll and avoid moving blocks B, and it is obvious also that if the ends of the roll are round instead of square, two set-screws may be used to hold the roll end being set diametrically opposite, and if set screws are used in _p_ to drive the wabbler they should be two in number, set diametrically opposite, and at a right angle to the two in the wabbler, so that it may act as a universal joint.

The method of automatically traversing the carriage C is as follows: Referring to Fig. 681, two gears _a_, _b_ are fast upon shaft _t_, gear _a_ drives _c_ which is on the same shaft as _e_, gear _b_ drives _d_ which drives a gear not seen in the cut, but which we will term _x_, it being on the same shaft as _c_ and _e_. Now if _e_ is driven through the medium of _a_ _c_, it runs in one direction, while if it is driven through the medium of _b_ _d_ _x_, it revolves _e_ in the opposite direction, and since _e_ drives _g_ and _g_ is on the end of the feed screw (E, Fig. 682) the direction of motion of carriage C is determined by which of the wheels _a_ or _b_ drives _e_. At _h_ is a stand affording journal bearing to a shaft _n_, whose end engages a clutch upon the shaft of wheels _c_, _x_ and _e_. On the outer end of shaft _n_ is ball lever _l´´_, whose lower end is attached to a rod _k_, upon which are stops _l l´_ adjustable along rod _k_ by means of set-screws. At _m_ is a bracket embracing rod _k_.

Now suppose carriage C to traverse to the left, and _m_ will meet _l_ moving rod _k_ to the left, the ball _i_ will move up to a vertical position and then fall over to the right, causing the clutch to disengage from gear _c_ and engage with the unseen gear _x_, reversing the motion of _e_ and of _g_, and therefore of carriage C, which moves to the right until _m_ meets _l´_ and pushes it to the right, causing _i_ to move back to the position it occupies in the engraving, the clutch engaging _c_, which is then the driving wheel for _e_.

SCREW MACHINE.--The screw machine is a special form of lathe in which the work is cut direct from the bar, without the intervention of forging operations, and it follows therefore that the bar must be large enough in diameter to suit the largest diameter of the work, the steps or sections of smaller diameter being turned down from the full size of the bar. The advantages of the screw machine are, that the work requires no centring since it is held in a chuck, that forging operations are dispensed with, that any number of pieces may be made of uniform dimensions without any measuring operations save those necessary when adjusting the tool for the first piece, and that it does not require skilled labor to operate the machine after the tools are once set.

The capacity of the screw machine is, therefore, many times greater than that of a lathe, while the diameters and lengths of the various parts of the work will be more uniform than can be done by caliper measurements, being in this case varied by the wear of the cutting edges of the tools only, which eliminates the errors liable to independent caliper measurement. Hollow work, as nuts and washers, may be equally operated on being driven by a mandril held in the chuck.

Fig. 691 represents Brown and Sharpe's Number 1 screw machine, which is designed for the rapid production of small work.

Three separate tool-holding devices may be employed: first, cutting tools may be placed in the holes shown to pierce (horizontally) the circular head F; second, tools may be fixed in the tool posts shown in the double slide rest, which has two slides (one in the front and one at the back of the line of centres); and third, tools may be placed in what may be termed the screw-cutting slide-rest J.

F is a head pierced horizontally with seven holes, and is capable of rotation upon L; when certain mechanism is operated L slides on D and the mechanism of these three parts is arranged to operate as follows. The lever arms K traverse L in D. When K is operated from right to left, L advances towards the live spindle until arrested at some particular point by a suitable stop motion, this stop motion being capable of adjustment so as to allow F to approach the live spindle a distance suitable for the work in hand.

When, however, K is operated from left to right L moves back, and when it has traversed a certain distance, the head F rotates 1/7 of a rotation, and becomes again locked so far as rotation is concerned. Now the relation between the seven holes in F is such that when F has rotated its 1/7 rotation, one of the seven holes is in line with the live spindle. Suppose then seven cutting tools to be secured in the holes in F, then K may be operated from right to left, traversing L and F forward, and one of the cutting tools will operate upon the work until L meets the stop; K may then be moved from left to right, L and F will traverse back, then F will rotate 1/7 rotation and L and F may be traversed by K, and a second tool will operate upon the work, and so on.

The diameter of the work is determined by the distance of the cutting edge of the tool from the line of centres, when such tool is in line with the work, or, in other words, is in position to operate upon the work. The end measurements of the work are secured by placing the cutting edges of the tools the requisite distance out from F, when L is moved forward as far as the stop motion will permit. But it is evident that the length of cut taken along the work, would under these simple conditions vary with the distance of the end of the work from the face of the chuck driving it, but this is obviated as follows:--

The live spindle is made hollow so that the rod of metal, of which the work is to be made, may pass through that spindle. A chuck on the spindle holds the work or releases it in the usual manner. Suppose then the chuck to be open and the bar free to be moved, then there is placed in the hole in F, that is in line with the work, a stop instead of a cutting tool. The end of the work may then, for the first piece turned, be squared up by a tool placed in the slide rest and then released from the chuck and pushed through the live spindle until it abuts against the stop so adjusted and affixed in the hole in F; K may then be operated to act on the work. The first tool may reduce the work to its largest required diameter, the second turn down a plain shoulder, the third may be a die cutting a thread a certain distance up the work, the fourth may be a tool turning a plain part at the beginning of the thread, the fifth may round off the end of the work, and the sixth may be a drill to pierce a hole a certain distance up the end of the work.

Fig. 691.

Fig. 692.]

Now suppose the work to require its edge at the other end to be chamfered, then there may be placed in the slide rest tool posts a tool to sever the work from the bar out of which it has been made, while the other may be used to chamfer the required edge, or to round it if needs be to any required form.

Work held in the chuck but not formed from a rod may be, of course, operated upon in a similar manner.

In the case, however, of work of large diameter requiring to be threaded, the threading tool may be held and operated differently and more rigidly as follows. I is a lever carrying under its bend and over the projecting end of the live spindle, a segment of a nut whose thread must equal in pitch the pitch of thread to be given to the work. A collar or ring, oftentimes called the leader, having a thread of the same pitch, is then secured upon the live spindle, so as to rotate with it, and have no end motion; when therefore I is depressed, the nut will come into work with the collar or ring, and I will be traversed at a speed proportioned to the pitch of the threads on the collar and nut.

Now I is attached to a shaft having journal bearing (and capable of end motion) at the back of the lathe head, and on this bar is attached the slide rest J, in which the turning or threading tool may be placed. The shaft above referred to having end motion, may be operated (when the nut in the lever I is lifted clear of the collar) laterally by means of the lever I; hence to traverse J to the right, or for the back traverse, I is raised and pulled to the right, I is then lowered, the nut engages with the collar, and the tool is traversed to the cut. The cut is adjusted for diameter by the slide rest, which is provided with an adjustable stop to determine the depth to which the tool shall enter the work.

It is obvious that this part of the machine, may be employed for ordinary turning operations, if the collar be of suitable pitch for the feed.

Figs. 692 and 693 represent A screw machine for general work.

A is a chuck with hardened steel [V]-shaped jaws. It is fast on the hollow arbor of the machine. B is a steadying chuck on the rear end of the arbor. The arbor has a two and one-sixteenth hole through it and its journals are very large and stiff. It is of steel, and runs in gun-metal boxes. The cone pulley and back gear is of the full proportion and power of an eighteen-inch lathe. C is an ordinary lathe carriage fitted to slide on the bed, and be operated by hand-wheel D and a rack pinion as usual. Across this carriage slides a tool rest E operated by screw as usual, and having two tool posts, one to the front and one to the rear of the work. This tool rest, instead of sliding directly in the carriage as is the case with lathes, slides on an intermediate slide which fits and slides in the carriage. This intermediate slide is moved in and out, a short distance only, by means of cam lever G. An apron on the front end of this slide carries the lead screw nut H. When the cam lever is raised it brings the slide outward about half an inch, and the tool rest E comes out with it and at the same time the nut leaves the lead screw. The inward movement of the slide is always to the same point, thus engaging the lead screw and resetting the tool. In cutting threads with a tool in the front tool post the tool is set by moving the tool rest as usual, and at the end of the cut the cam lever serves to quickly withdraw the tool and lead screw nut so that the carriage can be run back. The tool rest is then advanced slightly and the new cut taken. By this means threads are cut without any false motions, and the threads may be cut close up to a shoulder.

I is the lead screw. This screw does not extend, as is usual, to the head of the machine. It is short and is socketed into a shaft which runs to the head of the machine and is driven by gearing as usual. The lead screw is thus a plain shaft with a short, removable, threaded end. The gearing is never changed. Different lead screws are used for different threads, thus permitting threads to be cut without running back. The lead screws are changed in an instant by removing knob J. The lead screw nut H is a sectional nut, double ended, so that each nut will do for two pitches, by turning end for end in the apron. L is an adjustable stop which determines the position of the carriage in cutting off, facing, &c. K is an arm pivoted to the rear of the carriage and carrying three open dies like a bolt cutter head. At M is a block sliding or capable of being fed along the bed. N is a gauge screw attached to this block and provided with two nuts. The stop lever shown in the cut turns up to straddle this screw, and the position of the nuts determines how far each way the block may slide. O is the turret fitted to turn on the block. It has six holes in its rim to receive sundry tools. It can be turned to bring any of these tools into action, and is secured by the lock lever P.

The turret slide is moved quickly by hand, by means of the capstan levers U, which, by an in-and-out motion, also serve to lock the turret at any point. The turret slide is fed, in heavy work, by the crank-wheel R on its tail screw. This tail screw carries, inside the crank-wheel, two gears S, which are driven at different speeds by a back shaft behind the machine. These two gears are loose on the tail screw, and a clutch operated by lever T locks either one to the screw. Both the carriage and turret are provided with oil pots not shown in the cuts.

A top view of the turret is shown in Fig. 694, a set of tools being shown in place.

The end gauge which is shown removed from the chuck in Fig. 695, is composed of a hollow shank A fitting the hole in the turret, and a gauge rod B fitting the bore of the shank. The shank A may be set farther in or out of the turret, and the rod B may be set farther in or out of the shank, the two combined being so set that when the turret is clear back against its stop the end of the rod B will gauge the proper distance that the bar iron requires to project outwards from the chuck of the machine. The centre shown in Fig. 696 corresponds to an ordinary lathe centre, and is only used when chasing long work in steel.

The turner shown removed from the chuck in Fig. 697, consists of a hollow shank A, fitting the turret and having at its front end a hardened bushing B secured to A by a set screw. It has also a heavy mortised bolt C in the front lug of the shank; an end-cutting tool D shaped like a carpenter's mortising chisel, and clamped by the mortised bolt; a collar screw E to hold the tool endwise; and a pair of set-screws F to swivel the tool and its bolt. Bushing B is to suit the work in hand. The tool D is a piece of square steel hardened throughout. It is held by its bolt with just the proper clearance on its face. It cuts with its end without any springing, and will on this account stand a very keen angle of cutting edge. There is hardly any limit to its cutting power. It will cut an inch bar away at one trip with a coarse feed. It does not do smooth work, and is, therefore, used only to remove the bulk of the metal, leaving the sizer to follow.

The sizer Fig. 698, consists of a hollow shank A fitting the turret and carrying in its front end a hardened bushing B and a flat cutting tool C. The sizer follows the turner and takes a light finishing cut with oil or water, giving size and finish with a coarse feed, and having only a light and clean duty it maintains its size.

The die holder shown in Figs. 699 and 700, is arranged to automatically stop cutting when the thread is cut far enough along the work. It will cut a full thread cleanly up against a solid shoulder. It consists of a hollow shank A fitting the turret; a sleeve B fitted to revolve and slide on the front end of the shank C; a groove E bored inside the sleeve; a pin D on the shank fitting freely in the groove E; a keyway F at one point in the groove and leading out each way from it; and a thread die G held in the front end of the sleeve. When the turret is run forward, the thread die takes hold of the bolt to be cut, but it revolves idly instead of standing still to cut, until the pin D comes opposite the keyway F when, the turret still being moved forward, the pin enters the back of the keyway. The sleeve now stands still, the die cuts the thread and pulls the turret along by the friction of the pin in the keyway. Finally the turret comes against its front stop and can move forward no farther. Consequently the sleeve is drawn forward on its shank C, and the instant the pin D reaches the groove E the die and sleeve commence to revolve with the work and cease cutting. The machine is then run backward, and the turret moved back a trifle. This causes the pin to catch in the front end of the keyway and the sleeve is again locked. The die then unscrews, and, in doing so, pushes the turret back. A tap holder may be inserted in place of the die, and plug taps may be run to an exact depth without danger.

Drills and other boring tools are held in suitable sockets, which fit into the turret.

The following are the operations necessary to produce in this machine an hexagon-headed bolt.

First operation: The bar is inserted through the open chuck.

Second operation: Turret being clear back against its stop and revolved to bring present the end gauge, the bar is set against the end gauge, and the chuck is tightened. This chucks the bar and leaves the proper length projecting from the chuck.

Third operation: Front tool in the carriage, a bevelled side tool cones the end of the bar so turret tools will start nicely.

Fourth operation: Turret being revolved to present the turner, the bar is reduced, at one heavy cut, to near the proper size, the turret stop determining the length of the reduced portion.

Fifth operation: Turret being revolved to present the sizer, the body of the bolt is brought to exact size by a light, quick, sliding cut.

Sixth operation: Open die arm being brought down, the bolt is threaded; the left carriage stop indicating the length of the threaded part.

Seventh operation: Turret being revolved to present the die holder, the solid die is run over the bolt, bringing it to exact size with a light cut, and cutting _full thread to the exact point desired_.

Eighth operation: Front tool in the carriage chamfers off the end thread.

Ninth operation: Back tool of carriage, a parting tool, cuts off the bolt; the left carriage stop determining the proper length of head.

Tenth operation: Bolt being reversed in chuck, the top of the head is water cut finished by a front tool in the carriage. This operation is deferred till all the bolts of the lot are ready for it.

Fig. 703 represents a general view of a screw machine designed by Jerome B. Secor, of Bridgeport, Connecticut. The details of the machine are shown in Figs. 704, 705, 706, 707, 708, 709, 710, and 711.[13] The live spindle is of steel and is hollow, and its journals are ground. The boxes are lined with babbitt, so that no other metal touches the spindle, and may, by a special device, be re-babbitted and bored exactly parallel with the planing of the bed.

[13] From _Mechanics_.

A steel collar J, Fig. 704, between the front end of the forward box and the spindles, receives the thrust due to the cut, and a nut on the spindle acts against the cone to adjust it forward on a feather K in the spindle to take up end wear. The wire or rod from which the work is to be made is passed through the spindle and collar on the stand, and is held by a thumb-screw in the collar, which is influenced by the weight and cords, so that when the wire is released in the chuck the weight pulls the collar and wire forward, forcing the wire out through the front end of the chuck until it comes against the stop in the turret, which gauges the length needed to make the piece required. From time to time, as the rod is used up, the thumb-screw in the sliding collar is loosened, and the collar is shoved back on the rod as far as it will go, and the set-screw is again tightened.

Fig. 704 shows in section the front bearing and the automatic chuck. M is a hollow spindle within which is the hollow spindle H, through which the rod or wire to make the work passes. It is prevented from end motion by the cone hub on one side and the collar J on the other side of the bearing, while H may be operated endwise within M by means of the hand-lever shown on the left-hand of the headstock in the general view. The core A of the chuck screws upon M, and is threaded to receive the adjustment nut B, which receives and holds the adjustment wedges C at their ends by the talon shown. The shell D is secured to H by the screws I, which pass through slots in A, and therefore move endwise when H is operated by its hand-lever. Now the mouth of D, against which the adjustment wedges C rest, is coned 2-1/2°, as marked; hence the end motion of D to the left causes C, and therefore F, to approach the axis of the chuck and grip the rod or wire, while its motion to the right causes C, and therefore F, to recede from the chuck axis and to release the wire. Since B is screwed upon A, and C is guided at the end by B, and since also F is detained endwise in A, the motions of C and of F are at a right angle to the chuck axis. Hence in gripping the rod or wire there is no tendency to move it endways, as there is where the gripping jaws have, as in many machines, a certain amount of end motion while closing. When this end motion exists, tightening the jaws upon the work draws it away from the stop in the turret and impairs the adjustment for length of work. The gripping jaws are closely guided in slots in D and in A, and three sets of these jaws are necessary to cover a range of work from the full diameter of the bore of H down to zero. The capacity of each of these sets of jaws, however, may be varied as follows: The adjustment ring B is threaded upon A, and may be operated along A to move C endwise by means of the tangent screw E, whose threads engage with teeth parallel to the axis of B, and running across its width all around its circumference, hence rotating E, rotates B, causing it to move along A, and carry C beneath F. By this method of adjustment F need be given only enough motion to and from the chuck axis to grip and release the work, and the reduction of motion between the hand-lever operating H and the motion of F is so great, that with a very moderate force at the lever the wire may be held so that its projecting end may be twisted off without slipping the wire within the jaws or impairing the jaw grip.

Fig. 705 is a sectional and end view of the core A of the chuck, and Fig. 706 a sectional and end view of the shell D.

Fig. 707 represents a sectional side view and an end view of the cross slide, or cutting-off slide, which carries two tool posts, and therefore two cutting tools, one of which is at the back of the rest. In place of a feed screw and nut, or of a hand lever and link, it is provided with a segment of a gear-wheel P operating in a rack R, which avoids the tendency to twist the cross slides in its guides which exists when a hand lever and link is used.

The cross slide is adjusted to fit in its guideway by a jaw S^{1}, Fig. 707, which is firmly screwed to and recessed into R. To take up the wear, the face of S^{1} is simply reduced. This possesses a valuable advantage, because it is rigid and solid, does not admit of improper adjustment, nor can the adjustment become impaired at the hands of the operator.

To adjust the position of the cross slide upon the shears a screw passes between the shears and is threaded into the stud Q. This screw is operated by a hand wheel shown in the general view, Fig. 703, beneath the rear bearing of the headstock.

A special and excellent feature of the machine is the stop device for the motion of the cross slide which is shown in Fig. 707.

The screw S has one collar C, solid on it, and the screwed end is tapped into the sliding sleeve T, which is held from turning by the stud A. Between the solid collar C and the loose collar B there is a short, stiff spiral spring, as shown; by means of the fast and loose collars, the spring and the screwed thimble D, a strong friction is had on the collar B, which is ample to keep the screw from turning while in use as a stop, although it permits the screw to turn easily enough when a wrench is applied to the square end. Precisely the same device is used at the other end of the slide to stop it in the opposite direction.

Details of the mechanism of the turret and turret slide are shown in Figs. 708, 709, and 710. Fig. 708 is an end sectional view of the turret slide, which is traversed on its base by a segment D of a gear operating in a rack R (in the same manner as the cutting-off slide), the segment being connected by stud N to handle M. O represents the body of the slide, which is grooved at the sides to receive the gibs X, which secure it to the base P on which it slides. P is clamped to its adjusted position on the shears or bed by means of the gib, shown in dotted lines, which is pulled laterally forward by the screw S, which is tapped into the stem of the gib. The method of rotating the slide and of locking it in position is shown in Fig. 709, which is a top view of the turret head, and Fig. 710, which shows O removed from P and turned upside down. Pivoted to segment D is a rod E having at K a pin that as motion proceeds falls into S and rotates T, which is fast to the bottom of the turret. Upon the handle M being moved backward the segment begins its motion forward, as indicated by the arrow in Fig. 710, thereby moving the slide backward upon the gibs by the working of its cogs into the rack R, Fig. 708, which is attached to the base P. When the segment D has accomplished about one-half its motion the pin H, which is on the upper side of the segment D, comes in contact with the projection or lug on the side of the cam F, as shown by the arrow head in Fig. 710, bringing the opposite side of the cam against the pin G, Fig. 709, thereby moving it backward, compressing the spring U, and drawing the bolt L from its seat in the disc V. This operation is completed before the motion of the segment brings the pin K in contact with the ratchet-wheel T. The segment D in continuing its motion after the pin K is brought into the notch S, begins the revolution of the turret on its axis. As will be seen by the inspection of Fig. 710, the pin H works upon a much longer radius than the projection upon the cam with which it comes in contact, and therefore, after a given part of its motion is complete, gets beyond the reach of the cam, thereby releasing its hold and allowing the bolt L, Fig. 709, to be forced against the disc V by the expansion of the spring U, which occurs soon after the turret has commenced its revolution by the contact of pin K with the wheel T. The completion of the movement of the handle M (and the segment D) completes the revolution of the turret one-sixth of its circumference, thereby allowing the bolt L, by the further expansion of the spring U, to be forced into its next opening or seat in the disc V. The forward motion of the handle M brings the turret forward to its position at the work and restores the parts to their former positions, as shown in the illustrations.

The stop motion for the forward motion of M, and that therefore determines the length of turret traverse forward, and hence the distance each tool shall carry its cut along the work, is shown in Fig. 711. The end of the screw A abuts against the stop B in the usual manner; it is, however, threaded through the eye of a bolt C, as well as through the end of the turret slide, so that it may be locked by simply operating the nut D. Thus the use of a wrench is obviated, and the adjustment is more readily effected.

Figs. 712 and 713 represent a screw machine by the Pratt and Whitney Company, of Hartford, Connecticut, and having Parkhurst's patent wire or rod feed for moving the work through the hollow spindle and into position to be operated upon by the tools. The reference letters correspond in both figures.

At A is the front and at B the back bearing, affording journal bearing to a hollow spindle C, which carries the shell D of the work-gripping chuck, the clutch ring H and a collar I, in which is pivoted, at J, the clutch levers G. This collar is threaded upon C and is locked in position by a ring lock nut J´. The clutch arm K slides upon a rod X, and has a feather projecting into a spline in X. The core E of the work-gripping chuck is fast upon the inner spindle F, which revolves with the outer one C. The left-hand end of F abuts against the short arms of the clutch levers G, and it is obvious that when K is operated back and forth upon X, it moves the clutch H endways upon C, and the cone upon H operates the levers G, causing them to move the inner spindle F endways and the inner cone E of the chuck to open or close. Suppose, for example, that K (and hence H) is moved to the right, and the long ends of G will be released and may close moving their short ends away from the end of F, and therefore releasing E from its grip upon the work. In moving K to the right the sleeve L is also moved to the right, and its serrations at L´ being engaged with the tongue P, the sleeve M is pulled forward. Now the bar or rod of which the work is made is held at one end by the chuck, it is supported by the bushing Z in the end of spindle C, and in the bushing S in the arm of sleeve M, while it has fast upon it a collar T. When therefore M is pulled forward or to the right, its arm meets T and pulls the rod or bar for the work through the chuck E.

On the other hand when K and therefore H, L, and M, are moved to the left, levers G are opened at their long ends by the cone of H. The short ends of G push the inner spindle F to the right, E passes through D, and being split, closes upon the work and grips it, the parts occupying the positions shown in the figure. The same motion of K passes L through the sleeve M (the teeth at N raise the catch P, allowing L´ to pass through M) so that at the next movement of K to the right, M will be pulled a second step forward, again passing the work through the chuck. Q is merely a pin wherewith to lift P and enable M to be moved back, when putting in a new rod for the work; K is operated by a link from U to V, the handle for moving this link being shown at W in the general view.

To prevent the sleeve M from moving back with L it is provided with a shoe O, pressed by the spring R against X, thus producing a friction between M and X that holds M while L slides through it. R´ is to regulate the tension of the spring at R. _y_ is merely a sleeve to protect the clutch mechanism from dust, &c.

Box tools for screw machines are used for a great variety of special work. They are simply boxes or heads carrying tools and a work-steadying rest.

Fig. 714 represents a box tool for a screw machine. The cylindrical stem fits into the turret holes and contains a steadying piece or rest G to support the work and keep it to its cut. In the box tool shown in the figure, there are four cutting tools set in to the depth of cut by the screws A, B, C, and D respectively, and a fifth for rounding off the end of the work is shown at E.

Fig. 715 represents a top view, Fig. 715_a_ a front view, and Fig. 715_b_ an end view, of a box tool for shaping the handles for the wheels of the feeding mechanism of machines. The work is first turned true and to its required diameter, and the rest is set to just bear against the work to steady it and hold it against the pressure of the cut. The cutter is cylindrical with a gap cut in it at G, so as to give a cutting edge. By grinding the face of this gap the tool is sharpened without altering its shape, as is explained with reference to circular or disc tools for lathe work. The cutter is provided with a stem by which it is held in the slide, through the medium of the clamp. The slide is operated by an eccentric on the spindle or rod R, which is operated by the handle H. The stop obviously arrests the motion of the slide when it meets the box B, and this determines the diameter of the work, which is represented by W in the end view figure.

Fig. 716 represents the die holder and die for the Pratt and Whitney Co.'s screw machine. The die is cut through on four sides, and is enveloped by a split ring having a screw through its two lugs, so that by operating the screw the die may be closed to take up the wear and adjust it for diameter. It is secured in a collar by the set-screw shown, and this collar is clutch shaped on its back face, engaging a similar clutch face on the shoulder of the arbor, the object of this arrangement being as follows. Suppose it is required to cut a thread a certain distance, as say, 3/4 inch, along a stud, and that the depth of the clutch is 1/4 inch. Suppose that when the turret is fed forward sufficiently the thread is cut half an inch along the work at the moment that the turret meets its stop and comes to rest, then the die will continue to feed forward one-quarter of an inch, moving along the body or stem of the holder until its clutch face disengages, when the die will revolve with the work.

Fig. 717 represents a cutting-off tool and holder for a screw machine. The tool fits into a dovetail groove in the split end of the holder, and is ground taper in thickness to give the necessary clearance on the sides. It is held by the screw shown, which closes the split and grips the dovetail; obviously the top face only is ground to resharpen it.

Fig. 718 represents a special lathe for wood work designed and constructed by Charles W. Wilder, of Fitchburg, Massachusetts. It is intended to produce small articles in large quantities, cutting them to duplicate form and size without any further measurements than those necessary to set the tools in their proper respective positions. It is employed mainly for such work as druggists' boxes, tool handles, straight spokes for toy vehicles, piano pins, balls, rings, and similar work.

Its movements are such that the tools are guided by stops determining the length and the diameter of the work so as to make it exactly uniform, while the form of the cutting tools determines the form of the work, which must therefore be uniform.

The lathe may be described as one having a carriage rest spanning the bed of the lathe, which rest holds the work axially true with the lathe centres without the aid of the dead centre, while it at the same time trues the end of the work and leaves it free to be operated upon by other tools, which, after once being set and adjusted, shape any number of pieces of work to exact and uniform diameter and shape.

The manner in which this is accomplished is as follows: Fig. 718 is a general external view of the lathe; Fig. 719 is an end elevation view of the rest from the cone spindle end, and Fig. 720 is an end view of the rest viewed from the tailstock end of the lathe. A is a ring fastened in the rest R by the set-screw B. The mouth C of the ring which first meets the work is coned, or beveled, as shown, and an opening on one side of the ring admits a cutting tool T. Now the work is placed one end in the cone driving chuck on the lathe spindle, and the other end in the cone or mouth C, Fig. 719, being kept up to the driving chuck by the end pressure of C. As the work rotates, the tool T cuts it to the diameter D of the ring bore, the carriage or rest R traversing along the lathe bed as fast as tool cuts; hence the bore D serves as a guide to hold the work and make it run true, this bore being axially true with the lathe centres. The cone surface of C thus operates the same as the sole of an ordinary carpenter's plane, the tool T cutting more or less rapidly according as its cutting edge is set to project more or less in advance of the surface of the cone or recess C. This admits of the tool cutting at a rate of feed that may best suit the diameter of the work and the nature of the wood. The tool T, is operated laterally to increase or diminish the rate of feed by the screw E, which also serves as a pivot, so that by operating the thumb-screw F, the tool point may be adjusted for distance from the centre of the bore D, or in other words the diameter to which the tool T will turn the work is adjusted by the thumb-screw F. G is the head of the pivot screw that the swing tool holder H works upon, and this swing motion carries the forming tool or cutter X, which shapes the work to the required form. I is a shaft upon which a lever, carrying the tool holder J, works, the latter carrying the severing tool K, which severs the finished work from the stick of wood from which the work is made.

The tool holders H and J are connected by means of the arms L and M to the stud O, fast in wheel P, operated by a knee lever Q, which is pivoted at S to _u_, which is fast to one of the gibs that hold the carriage to the lathe [V]s. The knee lever Q is connected to the wheel P by a raw-hide strap, or belt V, so that the operator, by pressing his knee upon the end of the lever Q, causes the wheel P, to partly rotate, carrying O with it (O being fast in P), and gives a forward radial motion to tool holder H and cutter X, causing the latter to enter the work until such time as the stud O and the screw stud W are in line, horizontally with the centre of the wheel P, after which tool holder H will move back, while the severing tool K (which has a continuous upward or vertical movement) is cutting off the finished work, which has been formed to shape, and reduced to the required diameter by the forward movement of the tool or cutter X. The object of the backward or retiring motion of H is to relieve the shaping tool X from contact with the work, while K cuts it off, or otherwise the work might meet X when cut off, and receive damage from contact with it. The stud W, connecting tool holder H with the wheel P, is threaded with a right and left-hand screw, by operating which the tool X may be operated to reduce the work to any required diameter.

The rest or carriage R traverses along the lathe shears or bed Z, carrying with it all the levers and tools, so far described.

The tailstock, or back head, carries a tool holder in the rear of the spindle, in which fits also a drill bit or other cutting tool. The method of traversing and operating the carriage R and the back head is as follows:

At the back of the bed or shears is a table, shown at T, in Fig. 718. Upon this table is a stand to which is pivoted the end of a lever, as is shown at 1 in figure. This lever has a joint at 2, and is connected to the tailstock spindle at a joint marked 3. It is obvious that by operating the lever laterally, joint 2 will double, and the tail spindle will be moved along the bed. If the tail spindle is not locked it will simply feed through the tailstock and the tool in the spindle will operate, but if it is locked (by the ordinary screw shown), then the handle will slide the whole tailstock and the tool in the holder at the back of the tail spindle may operate.

At 4 is an adjusting screw, which, by coming into contact with the carriage R causes it also to traverse, which it will do until it meets against a screw on the other side, marked 5, in Fig. 718, which, standing farther out than the chuck prevents the cutting tool from meeting the chuck.

The movement of the carriage continues until the stop-gauge 6 meets the end of the work, hence the length of the work is from the cutting-off tool to the face of stop 6. The adjustment for the length of the work is made by means of screw 4, which will slide the carriage R, as soon as it meets it, independent of what distance the stop 6 may be from the work end. The tailstock carries two tool holders, similar to those on an ordinary lathe. When the cutting tools are used to cut completely over the end of the work, as in ball turning or a round ended handle, the stop 6 is not used, the tool which rounds the end acting as a stop of itself.

When bits are used they are held in the tail spindle and are made of a proper length to give the required depth of hole, or sometimes the face of the bit-holder may be used as a stop.

When the tools, cutters, and belts are all properly adjusted in position to cut to the required respective diameters or lengths the operator has simply to place a stick of wood in the lathe and operate the respective handles or levers in their proper consecutive order, and the work will be finished and cut off, the operation being repeated until the stick is used up, when a new one may be inserted, and so on.

LATHES FOR IRREGULAR FORMS.--In lathes for irregular forms (which are chiefly applied to wood and very rarely to metal turning), the work is performed by rotary cutting tools carried in a rapidly rotating head. The work itself is rotated slowly, and the carriage or frame carrying the cutting tools is caused to follow the outline of the pattern or _former_ at every point in its circumference as well as in its length. The principle of action by means of which these ends are attained is represented in Fig. 721, in which S represents a slide which carries the sliding head, affording journal bearing to the rotating head H, driven by the belt E, and carrying the cutters, and also the wheel W. F represents the pattern or former, and B a piece of wood requiring to be turned to the same form as that of F. Suppose then that F be slowly rotated by A and C, receiving rotary motion from A (through the medium of D), then the rotations of C will equal those of F, because the diameter of A is equal to that of C. The diameter of the circle described by the cutters at H is also equal to the diameter of W, hence the motion of the extremities of the cutters is precisely the same as that of the circumference of W, and as W receives its motion from F it is obvious that the cutters will reduce G to the same form and size as F, and if the head be traversed in the same direction as the axis of F, then the diameter and form of B will be made to correspond to that of F at every corresponding point throughout its length. Contact between W and F is maintained by means of a weight or spring, the rotation of F being sufficiently slow to insure its being continuous, while the necessary rapidity of cutting speed for the tools is attained by rotating H at the required speed of rotation.

This class of lathe is termed the "Blanchard" lathe from the name of the inventor, or "Lathe for irregular forms," from the chief characteristic of the work, but is sometimes designated from the special article it is intended to turn, as "The Shoe-last lathe," "Axe-handle lathe," "Spoke lathe," &c., &c.