Chapter VI: The Lathe (2)

The lead screw of a lathe is a screw for operating the lathe carriage when it is desired to cut threads upon the work. It is carried parallel to the lathe shears after the same manner as the independent feed spindle, and is operated by the change wheels shown in Fig. 492 at the end of the lathe. These wheels are termed change wheels on account of their requiring to be changed for every varying pitch of thread to be cut, so that their relative diameters, or, what is the same thing, their relative number of teeth, shall be such as to give to the lead screw the speed of rotation per lathe revolution necessary to cut upon the work a thread or screw of the required pitch.

The construction of the bearings which carry the lead screw in the S. W. Putnam's improved lathe is shown in Fig. 502, in which A represents the bearing box for the headstock end of the lathe, having the foot A´ as a base to bolt it to the lathe shears. L represents the lead screw, having on one side of A the collar L´ and on the other the nut and washer N and N´. The seat for the change wheel that operates the lead screw is at L´´, the stop pin _l_ fitting into a recess in the change wheel so as to form a driving pin to the lead screw. The washer N´ is provided with a feather fitting into a recess into L so that it shall rotate with L and shall prevent the nut N from loosening back as it would be otherwise apt to do. End motion to L is therefore prevented by the radial faces of L´ and N´.

At the other end of the lathe there are no collars on the lead screw, hence when it expands or contracts, which it will do throughout its whole length under variations of atmospheric temperature, it is free to pass through the bearing and will not be deflected, bent, or under any tension, as would be the case if there were collars at the ends of both bearings. The amount of this variation under given temperatures depends upon the difference in the coefficients of expansion for the metal of which the lead screw and the lathe shears are composed, the shears being of cast iron while lead screws are sometimes of wrought iron and sometimes of steel.

The bearings at both ends are split, with soft wood placed in the split and a screw to close the split and adjust the bearing bore to fit the journal, in the manner already described with reference to other parts of this lathe.

The construction of the swing frame for carrying the change wheels that go between the driving stud V, Fig. 494, and that on the seat L´´, Fig. 502, are as follows:--

Fig. 503 represents the change wheel swing frame, an edge view of which is partly shown at W in Fig. 494. S is a slot narrower at _a_ than at _b_. Into this slot fit the studs for carrying the change wheels.

By enabling a feed traverse in either direction the lathe carriage may be traversed back (for screw-cutting operations) without the aid of an extra overhead pulley to reverse the direction of rotation of the lathe, but in long screws it is an advantage to have such extra overhead pulley and to so proportion it as to make the lathe rotate quicker backwards than forward, so as to save time in running the carriage back.

The mechanical devices for transmitting motion from the lead screw to the carriage are shown in Fig. 504, representing a view from the end and one from the back of the lathe. B is a frame or casting bolted by the bolt _b_ to the carriage A of the lathe. C is a disk having a handle C´ and having rotary motion from its centre. Instead of being pivoted at its centre, however, it is guided in its rotary motion by fitting at _d_ _d_ into a cylindrical recess provided in B to receive it. C contains two slots D and D´ running entirely through it. These slots are not concentric but eccentric to the centre of motion of C. Through these slots there pass two stud bolts E and E´ shown by dotted lines in Fig. 504, and these bolts perform two services: first by reason of the nuts F and F´ they hold C to its place in B, and next they screw into and operate the two halves G and G´ of a nut.

Suppose, now, that the handle C´ be operated or moved towards arrow _e_, then the dot at _f_ being the centre of its motion and the slots D and D´ gradually receding from _f_ as their ends _g_ are approached they will cause E to move vertically upward and E´ to move vertically downward, a slot in B (which slot is denoted by the dotted lines _h_) guiding them and permitting this vertical movement.

Since E and E´ carry the two halves of the nut which envelops the lead screw L it is obvious that operating C´ will either close or release the half nuts from L according to which direction it (C´) is moved in.

The screws H and H´ screw tightly into B, and the radial faces of their heads are made to have a fair and full bearing against the underside of the shears, so that they serve as back gibs to hold the carriage to the shears and may be operated to adjust the fit or to lock the carriage to the bed if occasion may require. This lathe is made with a simple tool rest as shown in the engravings or with a compound slide rest. In some sizes the rest is held to the carriage by a weight upon a principle to be hereafter described. The bed is made (as is usual) of any length to suit the purposes for which the lathe is to be used.

The next addition to the lathe as it appears in the United States is that of a compound slide rest.

Fig. 505 represents a 28-inch swing lathe by the Ames Manufacturing Company, of Chicopee, Massachusetts. It is provided with the usual self-acting feed motion and also with a compound slide rest. The swing frame for the studs carrying the change wheels for screw cutting here swings upon the end of the lead screw, the same spindle that carries the driving cone for the independent feed rod which is in front of the lathe, also carries the driving gear for the change wheels used for screw cutting.

The construction of the compound rest is shown in Figs. 506 and 507. N is the nut for the cross-feed screw (not shown in the cut) and is carried in the slide A. A and the piece L above it are virtually in one, since the latter is made separate for convenience of construction and then secured to it firmly by screws. B is made separate from C also for convenience of construction and fixed to it by screws; L is provided with a conical circular recess into which the foot B of C fits. E is a segment of a circle operated by the set screw F to either grip or release B. The bolt D simply serves as a pivot for piece B C; at its foot C is circular and is divided off into the degrees of a circle to facilitate setting it to any designated angle.

If, then, F be unscrewed, C may be rotated and set to the required angle, in which position screwing up F will lock it through the medium of E. G is the feed nut for the upper slider H, which operates along a slide way provided on C, the upper feed screw having journal bearing at C´. I is the tool post, having a stepped washer J, by means of which the height of the tool K may be regulated to suit the work.

Suppose, now, that it be required to turn a shaft having a parallel and a taper part; then the carriage may be traversed to turn the parallel part, and the compound slide C may be set to turn the taper part, while the lower feed screw operating in N may be used to turn radial faces.

The object of making A and L in two pieces is to enable the boring and insertion of B, which is done as follows:--The front end of L as L´ is planed out, leaving in it a groove equal in diameter and depth to the diameter and depth of B, so that B may be inserted laterally along this groove to its place in L. The segment E is then inserted and a piece is then fitted in at L´ and held fast to A by screws. It is into this piece that the set screw F is threaded.

Various forms of construction are designed for compound rests, but the object in all is to provide an upper sliding piece carrying the tool holder, such sliding piece being capable of being so set and firmly fixed that it will feed the tool at an angle to the line of the lathe centres.

Another and valuable feature of the compound rest is that it affords an excellent method of putting on a very fine cut or of accurately setting the depth of cut to turn to an exact diameter; this is accomplished by setting the upper slide at a slight angle to the line of centres and feeding the tool to the depth of cut by means of the screw operating the upper slide. In this way the amount of feed screw handle motion is increased in proportion to the amount to which the tool point moves towards the line of lathe centres, hence a delicate adjustment of depth of cut may be more easily made.

Suppose, for example, that a cut be started and that it is not quite sufficiently deep, then, while the carriage traverse is still proceeding, the compound rest may be operated to increase the cut depth, or if it be started to have too deep a cut the compound rest may be operated to withdraw the tool and lessen its depth of cut. Or it may be used to feed the tool in sharp corners when the feed traverse is thrown out, or to turn the tops of collars or flanges when the tailstock is set over to turn a taper.

It is obvious, however, that comparatively short tapers only can be conveniently turned by a compound slide rest; but most tapers, however, are short.

To turn long tapers the tailstock of the lathe is set over as described with reference to the Putnam lathe, but for boring deep holes the slide rest must either be a compound one or a taper turning former or attachment must be employed.

When, however, the tailstock is set over, the centres in the work are apt to wear out of true and move their location (the causes of which will be hereafter explained).

In addition to this, however, the employment of a taper turning attachment enables the boring of taper holes without the use of a compound slide rest, thus increasing the capacity of the lathe not having a simple or single rest.

In Fig. 508 is shown a back view of a Pratt and Whitney weighted lathe having a Slate's taper turning attachment, the construction of which is as follows:--Upon the back of the lathe shears are three brackets having their upper surfaces parallel with and in the same plane as the surface of the lathe shears. Pivoted to the middle bracket is a bar which has at each end a projection or lug fitting into grooves provided in the end brackets, these grooves being arcs of a circle whose centre is the axis of the pivot in the middle bracket.

The end brackets are provided with handled nuts upon bolts, by which means the bar may be fixed at any adjusted angle to the lathe shears. Upon the upper surface of the bar is a groove or way in which slides a sliding block or die, so that this die in traversing the groove will move in a straight line but at an angle to the lathe bed corresponding to the angle at which the bar may be adjusted. The slide rest upon being connected by a bar or rod to the die or sliding block is therefore made to travel at the same angle to the lathe bed or line of centres as that to which the bar is set. The method of accomplishing this in the lathe, shown in Fig. 508, is as follows:--

In Fig. 509 A is the bar pivoted at C upon the centre bracket B; E is the sliding block pivoted to the nut bar F. This nut bar carries the cross-feed nut, which in turn carries the feed screw and hence the tool rest. When the nut bar is attached to the sliding block to turn a taper it is free to move endways upon the lower part of the carriage in which it slides, but when the taper attachment is not in use the bar is fastened to the lower part of the carriage by a set screw.

The screw at D is provided to enable an accurate adjustment for the angle of the bar A. G and H are screws simply serving to adjust the diameter to which the tool will turn after the manner shown in Fig. 588, G being for external and H for internal work.

When the lathe has a bed of sufficient length to require it, a slide is provided to receive the brackets, which may be adjusted to any required position along the slide, as shown in Fig. 510. This is a gibbed instead of a weighted lathe, and the method of attaching the sliding block to the lathe rest is as follows:--

A separate rod is pivoted to the sliding block. This rod carries at its other end a small cross head which affords general bearing to the end of the cross-feed screw, which has a collar on one side of the cross head and a fixed washer on the other, to prevent any end motion of the said screw.

The cross-feed nut is attached to the traversing cross slide. The other or handle end of the cross-feed screw has simple journal bearing in the slide rest, but no radial faces to prevent end motion, so that one may from the rod attached to the sliding-block traverse the cross-feed slide, which will carry with it the feed screw. As a result, the line of motion of the tool rest is governed by the sliding die, but the diameter to which the tool will turn is determined by the feed screw in the usual manner. When it is not required to use the taper attachment, the rod or spindle is detached from the sliding die and is locked by a clamp, when the rest may be operated in the usual manner.

Fig. 511 represents a compound duplex lathe of a design constructed by Sir Joseph Whitworth, of Manchester, England. The two rests are here operated on the same cross slide by means of a right and left-hand cross-feed screw.

The tool for the back rest is here obviously turned upside down.

The lead screw is engaged at two places by the feed nut, which is in two pieces attached to levers; while at a third point in its circumference it is supported by a bracket, bolted to the lathe bed.

Fig. 512 represents the New Haven Manufacturing Company's three tool slide rest, for turning shafting. It is provided with a follower rest, in front of which are two cutting tools for the roughing cuts, and behind which is a third tool for the finishing cut. The follower rest receives bushes, bored to the requisite diameter, to leave a finishing cut. The first tool takes the preliminary roughing cut; the second tool turns the shaft down to fit the bush or collar in the follower rest; and, as stated, the last tool finishes the work.

Fig. 513 represents a 44-inch swing lathe, showing an extra and detachable slide rest, bolted on one side of the carriage and intended for turning work of too large a diameter to swing over the slide rest. By means of this extra rest the cutting tool can be held close in the rest, instead of requiring to stand out from the tool-post to a distance equal to the width of the work. The ordinary tool post is placed in this extra rest.

When it is desired to bolt work on the lathe carriage and rotate the cutting tools, as in the case of using boring bars, the cross slide is sunk into instead of standing above the top surface of the carriage so as to leave a flat surface to bolt the work to, and [T]-shaped slots are provided in the carriage, to receive bolts for fastening the work to the carriage, an example of this kind being shown in Fig. 514.

Fig. 515 represents a self-acting slide or engine lathe by William Sellers and Co., of Philadelphia. These lathes are made in various sizes from 12 inches up to 48 inches swing on the same general design, possessing the following features:--The beds or shears are made with flat tops, the carriage being gibbed to the edges of the shears, these edges being at a right angle to the top face of the bed. The dead centre spindle is locked at each end of its bearing in the tailstock, thus securing it firmly in line with the live spindle. The ordinary tool feed is operated by a feed rod in front of the lathe, and this rod is operated by a disc feed, which may be altered without stopping the lathe so as to vary the rate of tool feed; and an index is provided whereby the operator may at once set the discs to give the required rate of feed. The lead screw for screw cutting is placed in a trough running inside the lathe bed, so that it is nearer to the cutting tool than if placed outside that bed, while it is entirely protected from the lathe cuttings and from dirt or dust; and the feed-driving mechanism is so arranged that both may be in gear with the live spindle, and either the rod feed or screw-cutting feed may be put into action instantly, while putting one into action throws the other out, and thus avoid the breakage that occurs when both may be put into action at the same time. The direction of the turning feed is determined by the motion of a lever conveniently placed on the lathe carriage, and the feed may be stopped or started in either direction instantly. The mechanism for putting the cross feed in action is so constructed (in those lathes having a self-acting cross feed) that the cross feed cannot be in action at the same time as the turning feed or carriage traverse by rod feed.

Lathes of 12 and 16 inches swing are back-geared, affording six changes of speed, and the lathe tool has a vertical adjustment on a single slide rest. Lathes of 20 inches swing are back-geared with eight changes of speed. Lathes of 25 inches and up to 48 inches swing inclusive are triple-geared, affording fifteen changes of speed, having a uniformly progressive variation at each change.

The construction of the live head or headstock for a 36-inch lathe is shown in the sectional side view in Fig. 516, and in the top view in Fig. 517, and it will be seen that there are five changes of speed on the cone, five with the ordinary back-gear, and five additional ones obtained by means of an extra pinion on the end of the back-gear spindle, and gearing with the teeth on the circumference of the face plate, the ordinary pinion of the back-gear moving on the back-gear spindle so as to be out of the way and clear the large gear on the cone spindle when the wheel of the extra back-gear pinion is in use, as shown in Fig. 517.

The front bearing of the live spindle is made of large diameter to give rigidity, and the usual collar for the face plate to screw against is thus dispensed with. End motion to the live spindle is prevented by a collar of hardened steel, this collar being fast on the live spindle and abutting on one side against the end face of the back bearing and on the other against a hardened steel thrust collar.

All these parts are enclosed in a tight cast-iron tail-block, which serves as an oil well to insure constant and perfect lubrication. The surfaces which confine the revolving collar back and front are so adjusted as to allow perfect freedom of rotary motion to the spindle and collar, but no perceptible end motion. The securing of the live spindle endwise is thus confined to the thickness of the steel collar only, and this is so enclosed in a large mass of cast iron as to insure uniformity of temperature in all its parts, hence there is no liability for the live spindle to stick or jam in its bearings, while the expansion of the live spindle endways from this collar (if it expands more than the lathe head) is allowed for in freedom of end motion through the front journal, which is a little longer than the bearing it runs in. In turning work held between the lathe centres the end thrust is taken against the hardened steel collar on the live spindle, and the hardened steel collar at the back of it, while in turning work chucked to the face plate the spindle is held in place endways by the confinement of the steel collar on the spindle between the steel collar behind it and the back end of the back bearing. With this arrangement of the spindle the change from turning between the lathe centres and turning chucked work requires no thought or attention to be given to any adjustment of the live spindle to accommodate it for the changed condition of end pressure between turning between the centres and turning chucked work, as is the case in ordinary lathes.

The double-geared lathes, as those of 12, 16 and 20 inches swing, are provided with face plates that unscrew from the live spindle to afford convenience for changing from one size of face plate to another, and all such lathes have their front live spindle journal made of sufficiently enlarged diameter above that of the screw, to afford a shoulder for the face plate to abut against. The nose of the live spindle is not threaded along its entire length, but a portion next to the shoulder is made truly cylindrical but without any thread upon it, and to this unthreaded part the face plate accurately fits so that it is held true thereby, and the screw may fit somewhat loosely so that all the friction acts to hold the face plate true and hard up against the trued face of the spindle journal. Face plates fitted in this way may be taken off and replaced as often as need be, with the assurance that they will be true when in place unless the surfaces have been abused in their fitting parts.

The construction of the tailstock or poppet-head, as it is sometimes termed, is shown in Figs. 518, 519, and 520. To hold it in line with the live spindle it is fitted between the inner edges of the bed, and it will be seen that one of the bed flanges (that on the left of the figure) is provided on its under side with a [V], and the clamp is provided with a corresponding [V], so that in tightening up the bolt that secures the tailstock to the bed the tailstock is drawn up to the edge of the shears, and therefore truly in line with the live spindle, while when this bolt is released the tailstock is quite free to be moved to its required position in the length of the bed. As a result of this form of design there is no wear between the clamp and the underneath [V], and the tailstock need not fit tightly between the edges of the bed, hence wear between these surfaces is also avoided, while the tailstock is firmly clamped against one edge of the bed as soon as the clamp is tightened up by the bolt on that side.

Fig. 520 shows the method of locking the tailstock spindle and of preventing its lateral motion in the bearing in the tailstock. At the front or dead centre end of this bearing there is between the spindle a sleeve enveloping the spindle, and coned at its outer end, fitting into a corresponding cone in the bore of the tailstock. Its bore is a fit to the dead spindle, and it is split through on the lower side. Its inner end is threaded to a sleeve that is within the headstock, and whose end is coned to fit a corresponding cone at the inner end of the bore of the tailstock.

To this second sleeve the line shown standing vertically on the left of the hand wheel is attached, so that operating this handle revolves the second sleeve and the two sleeves screw together, their coned ends abutting in their correspondingly coned seats in the tailstock bore, and thus causing the first-mentioned and split sleeve to close upon the dead centre spindle and yet be locked to the tailstock.

As the bore of the tailstock is exactly in line with the live spindle, it follows that the dead spindle will be locked also in line with it.

Figs. 521 and 522 represent sectional views of the carriage and slide rest of these lathes of a size over 16 inches swing. On the feed rod there are two bevel pinions P, one on each side of the bevel-wheel A, and by a clutch movement either of these wheels may be placed in gear with bevel-wheel A.

The clutch motion is operated by a lever which, when swung over to the right, causes the bevel pinion on the right to engage with the bevel-wheel A, and the carriage feeds to the right, while with the lever swung over to the left the carriage feeds to the left.

On the inclined shaft is a worm, or, as the makers term it, a spiral pinion of several teeth which gears into a straight toothed spur gear-wheel, giving a smooth and rolling tooth contact, and therefore producing an even and uniform feed motion.

This spur gear is fast on a shaft C, which is capable of end motion and is provided on each of its side faces with an annular toothed clutch. On each side of this spur-wheel is a clutch, one of which connects with the train of gears for the turning feed, and the other with the cross-feed gear B.

When the shaft (whose end is shown at C, and to which the spur gear referred to is fast) is pulled endways outwards from the lathe bed, its front annular clutch engages with the clutch that sets the cross-feed gear B in motion, and B engages with a pinion which forms the nut of the cross-feed screw.

When shaft C is moved endways inwards its other annular clutch engages the clutch on that side of it, and the turning feed is put into operation. The method of operating shaft C endways is as follows:--

In a horizontal bearing D is a shaft at whose end is a weighted lever L, and on the end of this shaft is a crank pin shown engaging a sleeve E which affords journal bearing to the outer end of shaft C, so that operating the weighted lever L operates E, and therefore shaft C with the spur gear receiving motion from the worm. A simple catch confines lever L to either of its required limits of motion, and allows the free motion of the operating lever to start or stop either the longitudinal or the cross feed, either of which is started or stopped by this lever, but no mistake can occur as to which feed is operated, because the catch above mentioned requires to be shifted to permit the feed to be operated.

The lower end of the bell crank F engages with the sleeve E, so that when the shaft C is operated outwards the horizontal arm of bell crank F is depressed and the spur pinion of the cross-feed nut is free to revolve, being driven by the cross-feed motion. When the lever F is moved towards the lathe bed (which occurs when the stop or catch is set to allow the longitudinal feed to be used) the nut of the cross feed is locked fast by the horizontal arm of the bell crank F. This device makes the whole action from one direction of feed to another automatic, and the attention of the workman is not needed for any complicated adjustment of parts preparatory to a change from one feed to the other.

At H is a hand wheel for hand feeding, the pinion R meshing into the rack that extends along the front of the lathe bed; back of the hand wheel and at H´ a clamp is provided whereby the saddle or carriage may be locked to the lathe bed when the cross feed is being used, thus obviating the use of a separate clamp on the bed.

The top slide of the compound rest is long and its guideway is short, the nut being in the stationary piece G, and it will be observed that by this arrangement at no time does the bearing surfaces of the slides become exposed to the action of chips or dirt.

Fig. 523 is a sectional view of the carriage and slide rest as arranged for 12 and 16-inch lathes when not provided with a self-acting cross feed. In this case end motion to shaft C is given by lever H, which is held in its adjusted position by the tongue T. In this lathe the screw-cutting and the turning feed cannot be put into gear at the same time.

The tool nut is arranged to enable the tool to be adjusted for height after it is fastened in the tool post by pivoting it to the cross slide, a spring S forcing it upwards at its outer end, thus holding the tool point down and in the direction in which the pressure of the cut forces it, thus preventing the wear of the pivot from letting the tool move when it first meets the cut. The nut N is operated to adjust the tool height, and at the same time enables the depth of cut to be adjusted very minutely. A trough catches the water, cuttings, &c., and thus protects the slides and slideways from undue wear.

In all these lathes the feeding mechanism is so arranged that there are no overhanging or suspended shaft pins or spindles, each of such parts having a bearing at each end and not depending on the face surface of a collar or pin, as is common in many lathes. Furthermore, in these lathes the handle for the hand carriage feed moves to the right when the carriage moves to the right; the cross-feed screw (and the upper screw also in compound slide rests) has a left-hand thread, so that the nut being fixed the slides move in the same direction as though the nut moved as in ordinary lathes. The tailstock or poppet-head screw is a right hand because the nut moves in this case. The object of employing right-hand screws in some cases, and left-hand ones in others, is that it comes most natural in operating a screw to move it from right to left to unscrew, and from left to right to screw up a piece, this being the action of a right-hand screw, left-hand screws being comparatively rarely used in mechanism, save when to attain the object above referred to.

Fig. 524 represents the Niles Tool Works car axle lathe, forming an example in which the work is driven from the middle of its length, leaving both ends free to be operated upon simultaneously by separate slide rests.

The work being driven from its centre enables it to rotate upon two dead centres, possessing the advantage that both being locked fast there is no liberty for the work to move, as is the case when an ordinary lathe having one live or running spindle is used, because in that case the live spindle must be held less firmly and rigidly than a dead centre, so as to avoid undue wear in the live spindle bearings; furthermore, the liability of the workman to neglect to properly adjust the bearings to take up the wear is avoided in the case of two dead centres, and no error can occur because of either of the centres running out of true, as may be the case with a rotating centre.

The cone pulley and back gear are here placed at the head of the lathe driving a shaft which runs between the lathe shears and drives a pinion which gears with the gear on the work driving head shown to stand on the middle of the shears. This head is hollow so that the axle passes through it. On the face of this gear is a Clement's equalizing driver constructed upon the principle of that shown hereafter in Fig. 756.

The means for giving motion to the feed screw and for enabling a quick change from the coarse roughing feed to a finer finishing feed to the cutting tool without requiring to change the gears or alter their positions, is shown in Fig. 525. _a_ and _b_ are two separate pinions bored a working fit to the end of the driving shaft S, but pierced in the bore with a recess and having four notches or featherways _h_. The end of the driving shaft S is pierced or bored to receive the handled pin _i_, and contains four slots to receive the four feathers _j_ which are fast in _i_. In the position shown in the figure these feathers engage with neither _a_ nor _b_, hence the driving shaft would remain motionless, but it is obvious that if pin _i_ be pushed in the feathers would engage _b_ and therefore drive it; or if _i_ were pulled outwards the feathers would engage _a_ and drive it, because _a_ and _b_ are separate pinions with a space or annular recess between them sufficient in dimensions to receive the feathers. The difference in the rate of feed is obviously obtained through the difference in diameters of the pair of wheels _a_, _c_ and the pair _d_, _b_, the lathe giving to the lead screw the slowest motion and, therefore, the finest feed.

The means for throwing the carriage in and out of feed gear with the feed screw and of providing a hand feed for operating the tool in corners or for quickly traversing the carriage, is shown in Fig. 526, in which S represents the feed screw and B a bracket or casting bolted to the carriage and carrying the hand wheel and feed mechanism shown in the general cut figure.

B provides a slide way denoted by the dotted lines at _b_, for the two halves N and N´ of the feed nut. It also carries a pivot pin shown at _p_ in the front elevation, which screws into B as denoted by _p´_ in the end view; upon this pivot operates the piece D, having the handle _d_. In D are two cam grooves _a_ _a_; two pins _n_, which are fast in the two half-nuts N N´, pass through slots _c_ _c_ in B, and into the cam grooves _a_ _a_ respectively.

As shown in the cut the handle _d_ of D is at its lowest point, and the half-nuts N´ and N are in gear upon the feed screw; but suppose _d_ be raised, then the grooves _a_ _a_ would force their respective pins _n_ up the slots _c_, and these pins _n_ being each fast to a half of the nut, the two half-nuts would be opened clear of the feed screw, and the carriage would cease to be fed.

The hand-feed or guide-carriage traverse motion is accomplished as follows:--B provides at _e_ journal bearing to a stud on which is the hand wheel shown in the general cut; attached to this hand wheel is a pinion operating a large gear (also seen in general cut) whose pitch line is seen at _g_, in figure. The stud carrying _g_ has journal bearing at _f_, and carries a pinion whose pitch circle is at _h_ and which gears with the rack.

Fig. 527, which is taken from _The American Machinist_, represents an English self-acting lathe capable of swinging work of 12 inches diameter over the top of the lathe shears, which are provided with a removable piece beneath the live centre, which when removed leaves a gap, increasing the capacity of the lathe swing. The gears for reversing the direction of feed screw motion are here placed at the end of the live head or headstock, the screw being used for feeding as well as for screw cutting.

Fig. 528 represents a pattern-maker's lathe, by the Putnam Tool Co., of Fitchburg, Massachusetts. This lathe is provided with convenient means of feeding the tool to its cut by mechanism instead of by hand, as is usually done by pattern-makers, and this improvement saves considerable time, because the necessity of frequently testing the straightness of the work is avoided.

It is provided with an iron extension shears, the upper shears sliding in [V]-ways provided in the lower one. The hand-wheel is connected with a shaft and pinion, which works in a rack, and is used for the purpose of changing the position of the upper bed, which is secured in its adjusted position by means of the tie bolts and nuts, as shown on the front of the lower shears. This enables the gap in the lower shears to be left open to receive work of large diameter, and has the advantage that the gap need be opened no more than is necessary to receive the required length of work. The slide-rest is operated by a worm set at an angle, so as to operate with a rolling rather than a sliding motion of the teeth, and the handle for operating the worm-shaft is balanced. The carriage is gibbed to the bed. The largest and smallest steps of the cone pulley are of iron, the intermediate steps being of wood, and a brake is provided to enable the lathe to be stopped quickly. This is an excellent improvement, because much time is often lost in stopping the lathe while running at a high velocity, or when work of large diameter is being turned. The lathe will swing work of 50 inches within the gap, and the upper shears will move sufficiently to take in 4 additional feet between the centres.

In the general view of the lathe, Fig. 528, the slide-rest is shown provided with a [T]-rest for hand tools, but as this sets in a clip or split bore, it may readily be removed and replaced by a screw tool, poppet for holding a gauge, or other necessary tool. To enable the facing of work when the gap is used, the extra attachment shown in Figs. 529 and 530 is employed. It consists of an arm or bar A, bolted to the upper shears S by a bolt B, and clamp C, in the usual manner, and is provided with the usual slideway and feed-screw _f_ for operating the lower slide T, which carries a hollow stem D; over D fits a hub K, upon the upper slide E, which hub is split and has a bolt at F, by means of which the upper slide may be clamped to its adjusted angle or position. The upper slider H receives the tool-post, which is parallel and fits in a split hub, so that when relieved it may be rapidly raised or lowered to adjust the height of the tool.

The construction of the brake for the cone pulley is shown in Figs. 531 and 532, in which P represents the pulley rim, L the brake lever, S a wooden shoe, and W a counter-weight. The lever is pivoted at G to a lug R, provided on the live headstock, and the brake obviously operates on the lowest part of the cone flange; hence the lever handle is depressed to put the brake in action.

Fig. 527.

Fig. 528.

Fig. 529.]

The construction of the front and back bearings for the live spindle is the same as that shown in Figs. 495 and 496.

Wood turners sometimes have their lathes so made that the headstock can be turned end for end on the lathe shears, so that the face plate may project beyond the bed, enabling it to turn work of large diameter. A better method than this is to provide the projecting end of the lathe with a screw to receive the face plate as shown in Fig. 533, which represents a lathe constructed by Walker Brothers of Philadelphia. At the end of the lathe is shown a hand rest upon a frame that can be moved about the floor to accommodate the location, requiring to be turned upon the work.

For very large work, wood-workers sometimes improvise a facing lathe, as shown in Fig. 534, in which A is a headstock bolted to the upright B; C is the cone pulley, and E a face plate built up of wood, and fastened to an iron face plate by bolts. The legs A, of the tripod hand rest, Fig. 535, are weighted by means of the weights B.

In Fig. 536 is shown a chucking lathe, especially adapted for boring and facing discs, wheels, &c. The live spindle is driven by a worm-wheel, provided around the circumference of the face plate. The driving worm (which runs in a cup of oil) is on a driving shaft, running across the lathe and standing parallel with the face of the face plate. This shaft is driven by a pulley as shown, changes of speed being effected by having a cone pulley on the counter-shaft and one on the line of shafting.

This lathe is provided with two compound slide rests. One of which may be used for boring, while the other is employed for facing purposes. These rests are adjustable for location across the bed of the lathe by means of bolts in slots, running entirely across the lathe bed.

These slide rests are given a self-acting motion by the following arrangement of parts: at the back of the live spindle is an eccentric rod, operating a connecting rod, which is attached at its lower end to the arm of a shaft running beneath the bed, and parallel to the lathe spindle. This shaft passes beyond the bed where it carries a bevel gear-wheel, which meshes with a bevel gear-wheel upon a cross shaft. This cross shaft carries three arms, one at each end and inside its journal bearings in the bed, and one beneath and at a right angle to the other two. These receive oscillating motion by reason of the eccentric connecting rod, &c.

For each compound rest there are provided two handles as usual, and in addition an [L] lever, one arm of the latter being provided with a series of holes, while the other carries a weight.

The [L] lever carries a pawl which operates a ratchet wheel, placed on the handle end of the slide rest cross feed screw. If then a chain be attached to one of the holes of the [L] lever, and to the oscillating arm, the motion in one direction of the latter will be imparted to the [L] lever (when the chain is pulled). On the return motion of the oscillating arm, the chain hangs loose, and the weight on the [L] lever causes that lever arm to fall, taking up the slack of the chain, the feed taking place (when the pawl is made to engage with the ratchet wheel) during the motion of the oscillating arm from right to left, or while pulling the chain.

The rate of feed is varied by attaching the chain to different holes in the [L] lever.

To operate the rests in a line parallel to the lathe spindle, a similar [L] lever is attached by chain to the third oscillating arm, which is placed on the cross shaft, mid-way of the bed, or between the two slide rests. It is obvious then that with an [L] lever attachment on each feed screw, both slides of each rest may be simultaneously operated, while either one may be stopped either by detaching the chain or removing the [L] lever.

For operating the rests by hand, the usual feed-screw handles are used.

Fig. 537 represents a 90-inch swing lathe by the Ames Manufacturing Company of Chicopee, Massachusetts.

The distinguishing feature of this lathe is that the tailstock spindle is made square, to better enable it to bear the strain due to carrying cutting tools in place of the dead centre; and by means of a pulley instead of a simple hand wheel for operating the tail spindle, that spindle may be operated from an overhead countershaft, and a tool may be put in to cut key-ways in pulleys, wheels, &c., chucked on the face plate (which of course remains stationary during the operation), thus dispensing with the necessity of cutting out such key-ways by hammer, chisel, and file, in wheel bores too large and heavy to be operated upon in a slotting machine.

On account of the weight of the tailstock it is fitted with rollers, which may be operated to lift it from the bed when it is to be moved along the lathe bed.

Fig. 536.

Fig. 537.]

Fig. 538 represents a 50-inch swing lathe by the New Haven Manufacturing Company of New Haven, Connecticut. The compound rest is here provided with automatic feed so that it may be set at an angle to bore tapers with a uniform feed. The tailstock is provided with a bracket, carrying a pinion in gear with the hand-feed rack, so as to move the tailstock along the bed by means of the pinion. The feed screw is splined to give an independent feed, and the swing frame is operated by a worm as shown.

GAP LATHE OR BREAK LATHE.

The gap lathe is one in which the bed is provided with a gap beneath the face plate, so as to enable that plate or the chucks to swing work of larger diameter, an example being given in Fig. 539.

It is obvious, however, that the existence of the gap deprives the slide rest of support on one side, when it is used close to the face plate. This is obviated in some forms of gap lathes by fitting into the gap a short piece of bed that may be taken out when the use of the gap is required.

The gap lathe has not found favor in the United States, the same result being more frequently obtained by means of the extension lathe, which possesses the advantages of the gap lathe, while at the same time enabling the width of the gap to be varied to suit the length of the work. Fig. 540 represents an extension lathe by Edwin Harrington and Son, of Philadelphia. There are two beds A and B, the former sliding upon the latter when operated by the hand-wheel E, which is upon the end of a screw that passes between the two beds, has journal bearing in the upper bed, and engages a nut in the lower one, so that as the screw is operated the wheel moves longitudinally with the upper bed. C is the feed rod which communicates motion to the feeding screw D, which has journal bearing on the upper bed and therefore travels with it when it is moved or adjusted longitudinally. The cross slide has sufficient length to enable the slide rest to face work of the full diameter that will swing in the gap, and to support the slide rest when moved outwards to the full limit, it is provided with a piece F, which slides at its base upon the guideway or slide G.

Fig. 541 represents a double face plate lathe such as is used for turning the wheels for locomotives. The circumference of both the face plates are provided with spur teeth, so that both are driven by pinions, which by being capable of moving endways into or out of gear, enable either face plate to be used singly, if required, as for boring purposes.

The slide rests are operated by ratchet arms for the self feed, these arms being operated by an overhead shaft, with arms and chains.

Fig. 542 represents a chucking lathe adapted more especially for boring purposes. Thus the cone pulley is of small diameter and the parts are light, so that the lathe is more handy than would be the case with a heavier built lathe, while at the same time it is sufficiently rigid for large work that is comparatively light.

The compound rest is upon a pedestal that can be bolted in any required position on the lower cross slide, and is made self-acting for the feed traverse by the change wheels and feed screw, while the self-acting cross feed is operated by a ratchet handle, actuated by a chain from an overhead reciprocating lever; the latter being actuated from the crank pin at A, which is adjustable in a slot in the crank disk B. A lathe of this kind is very suitable for brass work of unusually large diameter, because in such work the cuts and feeds are light, and the cutting speed is quick, hence a heavy construction is not essential.

Figs. 543 and 544 represent a large lathe built by Thomas Shanks and Co., of Johnstone, near Glasgow, Scotland; all the figures of this lathe being from _The American Machinist_.

Fig. 543 shows the headstock and two of the slide rests, while Fig. 544 represents the remainder of the bed, the tailstock, and two of the slide rests.

It will be seen from the figures that there are a compound rest and a column or pillar rest both at the front and at the back of the lathe, and that there is an additional rest on the front end of the tailstock which may be used for facing the ends of the work.

Fig. 545 represents a section through, and a partial plan of the headstock, and it will be seen that the live spindle is free from the cone pulley and from the gearing, the chuck plate being driven from a pinion engaging an internal gear at the back of the chuck plate. By this construction the balancing of such work as crank shafts is facilitated, because the chuck plate is not affected by the friction of the driving gears, and may therefore be easily revolved to test the balance of the work.

Fig. 546 represents a cross section through the bed, and through one of the compound rests, and one of the pillar rests, the latter rests being made thin so that they may pass between the cheeks of crank shafts, to turn their faces and the crank journals.

Fig. 547 represents a view from the back end of the headstock, and Fig. 548 a view of the lathe from the tailstock end.

Figs. 549 and 550 represent a plan and a side view of the headstock and the two slide rests nearest to it. The lathe being shown at work on the crank shaft of the steamship service, which is shown in dotted lines, and it will be seen that for turning the stem of the shaft all the rests can be used at once, those at the back of the lathe having their cutting tools turned upside down (as will be more clearly seen in the cross-sectional view of the rests in Fig. 546).

Figs. 551 and 552 represent a plan and a side view of the other half of the lathe in operation upon the same crank shaft, which is again shown in dotted lines.

Referring now to the general construction of the lathe, the headstock or live spindle has a front journal bearing 18 inches diameter and 24 inches long, and a back bearing 12 inches diameter and 15 inches long, the bearings being parallel. The driving cone has five changes of speed for a 6-inch belt, and is carried on an independent spindle. The cone is turned inside as well as outside, so as to be in balance at high speeds.