This, however, is a theoretical, rather than a practical point, as may be perceived from Fig. 684, in which r is a part of a section of a roll, and w a part of a section of a wheel. Now, assuming that the V-ways were as much as even a sixteenth out of true, so far as height is concerned, all the influence of the variation in height is shown by the second line of emery-wheel perimeter, shown in the figure, the two arcs being drawn from centres, one of which is ¹⁄₁₆th inch higher than the other. It is plain, then, that with the ordinary errors found in such V-guideways, which will not be found to exceed ¹⁄₃₀th of an inch, no practical effect will be produced upon the roll. Again, if one V is not in line with the other, no practical effect is produced, because if the carriage c were inclined at an angle, though the plane of rotation of the emery-wheel would be varied, its face would yet be parallel to the roll axis. If the Vs were to vary in their widths apart (the angles of the Vs being 45° apart), all the effect it would have would be to raise or lower the carriage c to one-half the amount the Vs were in error. It will be thus perceived that correctness of the roll both for parallelism and cylindricity is obtained independent of absolute truth in the V-guides.

Referring now to some of the details of construction of the lathe, the slide rest a, Fig. 683, is bored to receive sockets d d, Fig. 685, and is provided with caps, so that the sockets may be firmly gripped and held axially true one with the other. The socket-bores are taper, to receive the taper ends of the arbor x, and are provided with oil pockets at each end. There is a driving pulley on each side of the emery-wheel, and equal belt-speed is obtained as follows: Two belt driving drums m n are employed, and each belt passes over both, as in Figs. 683 and 685, and down around the pulleys p. The diameter of the drum n is less than the diameter of the drum m by twice the thickness of the belt, thus equalizing inside and outside belt diameters, since they both pass over the pulley of the emery-arbor. The piece t is a guard to catch the water from the emery-wheels, and is hinged at the back so that the top is a lid that may be swung back out of the way when necessary.

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.

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.

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 2¹⁄₂°, 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 s¹, Fig. 707, which is firmly screwed to and recessed into r. To take up the wear, the face of s¹ 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.