Chapter VI: The Lathe (1)

The lathe may be justly termed the most important of all metal-cutting machine tools. Not only on account of the rapidity of its execution which is due to its cutting continuously while many others cut intermittently, but also because of the great variety of the duty it will perform to advantage. In the general operations of the lathe, drilling, boring, reaming, and other processes corresponding to those performed by the drilling machine, are executed, while many operations usually performed by the planing machine, or planer as it is sometimes termed, may be so efficiently performed by the lathe that it sometimes becomes a matter of consideration whether the lathe or the planer is the best machine to use for the purpose.

The forms of cutting tools employed in the planer, drilling machine, shaping machine, and boring machine, are all to be found among lathe tools, while the work-holding devices employed on lathe work include, substantially, very nearly all those employed on all other machines and, in addition, a great many that are peculiar to itself. In former times, and in England even at the present day, an efficient turner (as a lathe operator is termed), or lathe hand, is deemed capable of skilfully operating a planer, boring machine, screw-cutting machine, drilling machine, or any of the ordinary machine tools, whereas those who have learned to operate any or all of those machine tools would prove altogether inefficient if put to operate a lathe.

In almost all the mechanic arts the lathe in some form or other is to be found, varying in weight from the jewellers' lathe of a few pounds to the pulley or fly-wheel lathe of the engine builder, weighing many tons.

The lathe is the oldest of machine tools and exists in a greater variety of forms than any other machine tool. Fig. 479 represents a lathe of primitive construction actually in use at the present day, and concerning which the "Engineering" of London (England), says, "At the Vienna Exhibition there were exhibited wood, glasses, bottles, vases, &c., made by the Hucules, the remnant of an old Asiatic nation which had settled at the time of the general migration of nations in the remotest parts of Galicia, in the dense forests of the Carpathian Mountains. The lathe they are using has been employed by them from time immemorial. They make the cones _b_, _b_ (of maple) serve as centres, one being fixed and the other movable (longitudinally). They rough out the work with a hatchet, making one end _a_ cylindrical, to receive the rope for giving rotary motion. The cross-bar _d_ is fastened to the trees so as to form a rest for the cutting tool, which consists of a chisel." C, of course, is the treadle, the lathe or pole being a sapling.

In other forms of ancient lathes a wooden frame was made to receive the work-centres, and one of these centres was carried in a block capable of adjustment along the frame to suit different lengths of work. In place of a sapling a pole or lath was employed, and from this lath is probably derived the term lathe.

It is obvious, however, that with such a lathe no cutting operation can be performed while the work is rotating backwards, and further, that during the period of rest of the cutting tool it is liable to move and not meet the cut properly when the direction of work rotation is reversed and cutting recommences, hence the operation is crude in the extreme, being merely mentioned as a curiosity.

The various forms in which the lathe appears in ordinary machine shop manipulation may be classified as follows:--

The _foot lathe_, signifying that the lathe is driven by foot.

The _hand lathe_, denoting that the cutting tools must be held in the hands, there being no tool-carrying or feeding device on the lathe.

The _single-geared lathe_, signifying that it has no gear-wheels to reduce the speed of rotation of the live spindle from that of the cone.

The _back-geared lathe_, in which gear-wheels at the back of the headstock are employed to reduce the speed of the lathe.

The _self-acting lathe_, or _engine lathe_, implying that there is a slide rest actuated automatically to traverse the tool to its cut or feed.

The _screw-cutting lathe_, which is provided with a _lead_ screw, by means of which other screws may be cut.

The _screw-cutting lathe with independent feed_, which denotes that the lathe has two feed motions, one for cutting threads and another for ordinary tool feeding; and

The _chucking lathe_, which implies that the lathe has a face plate of larger diameter than usual, and that the bed is somewhat short, so as to adapt it mainly to work held by being chucked, that is to say, held by other means than between the lathe centres.

There are other special applications of the lathe, as the boring lathe, the grinding lathe, the lathe for irregular forms, &c., &c.

This classification, however, merely indicates the nature of the lathe with reference to the individual feature indicated in the title; thus, although a foot lathe is one run by foot, yet it may be a single or double gear (back-geared) lathe, or a hand or self-acting lathe, with lead screw and independent feed motion.

Again, a hand lathe may have a hand slide rest, and in that case it may also be a back-geared lathe, and a back-geared lathe may have a hand slide rest or a self-acting feed motion or motions.

Fig. 480 represents a simple form of foot lathe. The office of the shears or bed is to support the headstock and tailstock or tailblock, and to hold them so that the axes of their respective spindles shall be in line in whatever position the tailstock may be placed along the bed. The duty of the headstock is to carry the live spindle, which is driven by the cone, the latter being connected by the belt to the wheel upon the crank shaft driven by the crank hook and the treadle, which are pivoted by eyes W to the rod X, the operation of the treadle motion being obvious. The work is shown to be carried between the live centre, which is fitted to the live spindle, and the dead centre fitting into the tail spindle, and as it has an arm at the end, it is shown to be driven by a pin fixed in the face plate, this being the simplest method of holding and driving work. The lathe is shown provided with a hand tool rest, and in this case the cutting tools are supported upon the top of the tool rest N, whose height may be adjusted to bring the tool edge to the required height on the work by operating the set screw S, which secures the stem of N in the bore of the rest.

To maintain the axes of the live and dead spindles in line, they are fitted to a slide or guideway on the shears, the headstock being fixed in position, while the tailstock is adjustable along the shears to suit the length of the work.

To lock the tailstock in its adjusted position along the shears, it has a bolt projecting down through the plate C, which bolt receives the hand nut D. To secure the hand rest in position at any point along the shears, it sets upon a plate A and receives a bolt whose head fits into a [T]-shaped groove, and which, after passing through the plate P receives the nut N, by which the rest is secured to the shears.

To adjust the end fit of the live spindle a bracket K receives an adjusting screw L, whose coned end has a seat in the end J of the live spindle, M being a check nut to secure L in its adjusted position.

The sizes of lathes are designated in three ways, as follows:--First by the _swing_ of the lathe and the total length of the bed, the term _swing_ meaning the largest diameter of work that the lathe is capable of revolving or swinging. The second is by the _height of the centres_ (from the nearest corner of the bed) and the length of the shears. The height of the centres is obviously equal to half the swing of the lathe, hence, for example, a lathe of 28-inch swing is the same size as one of 14-inch centres. The third method is by the swing or height of centres and by the greatest length of work that can be held between the lathe centres, which is equal to the length of the bed less the lengths of the head and tailstock together.

The effective size of a lathe, however, may be measured in yet another way, because since the hand rest or slide rest, as the case may be, rests upon the shears or bed, therefore the full diameter of work that the lathe will swing on the face plate cannot be held between the centres on account of the height of the body of the hand rest or slide rest above the shears.

Fig. 481 shows a hand lathe by F. E. Reed, of Worcester, Massachusetts, the mechanism of the head and tail stock being shown by dotted lines. The live spindle is hollow, so that if the work is to be made from a piece of rod and held in any of the forms of chucks to be hereafter described, it may be passed through the spindle, which saves cutting the rod into short lengths. The front bearing of the headstock has two brasses or boxes, A and B, set together by a cap C.

The rear bearing has also a bearing box, the lower half D being threaded to receive an adjustment screw F and check nut G to adjust the end fit of the spindle in its bearings. In place of grooved steps for the belt the cone has flat ones to receive a flat belt.

The tail spindle is shown, in Fig. 482, to be operated by a screw H, having journal bearing at I, and threaded into a nut fast in the tail spindle at J. To hold the tail spindle firmly the end of the tail stock is split, and the hand screw K may be screwed up to close the split and cause the bore at L to clasp the tail spindle at that end.

To lock the tail stock to the shears the bolt M receives the lever N at one end and at the other passes through the plate or clamp O, and receives the nut P, so that the tail stock is gripped to or released from the shears by operating N in the necessary direction. The hand rest, Fig. 483, has a wheel W in place of a nut, which dispenses with the use of a wrench.

What are termed bench lathes are those having very short legs, so that they may for convenience be mounted on a bench or fastened to a second frame, as shown in Fig. 484.

It is obvious that when work is turned by hand tools, the parallelism of the work depends upon the amount of metal cut off at every part of its length, which to obtain work of straight outline, whether parallel or taper, involves a great deal of testing and considerable skill, and to obviate these disadvantages various methods of carrying and accurately guiding tools are employed. The simplest of these methods is by means of a slide rest, such as shown in Fig. 485.

The tool T is carried in the tool post P, being secured therein by the set screw shown, which at the same time locks the tool post to the upper slider. This upper slider fits closely to the cross slide, and has a nut projecting down into the slot shown in the same, and enveloping the cross feed screw, whose handle is shown at C, so that operating C traverses the upper slider on the cross slide and regulates the depth to which the tool enters the work, or in other words, the depth of cut.

The cross slide is formed on the top of the lower slider, which has beneath a nut for the feed screw, whose handle is shown at A, hence rotating A will cause the lower slider to traverse along the lower slide and carry the tool along the work to its cut. To maintain the fit of the sliders to the slides a slip of metal is inserted, as at _e_ and at _c_, and these are set up by screws as at _f_, _f_ and _b_, _b_.

The lower or feed traverse slide is pivoted to its base B, so that it may be swung horizontally upon the same, and is provided with means to secure it in its adjusted position, which is necessary to enable it to turn taper as well as parallel work. To set this lower slide to a given degree of angle it may be marked with a line and the edge of base B may be divided into degrees as shown at D.

When a piece of work is rotated between the lathe centres its axis of rotation may be represented by an imaginary straight line and the lower slides must, to obtain parallel work, be set parallel to this straight line, while for taper work the slide rest must be set at an angle to it. Now, in the form of slide rest shown in figure the cross slide is carried by the lower or feed traverse slide, hence setting the lower slide out of parallel with the work axis sets the cross slide out of a right angle to the work axis, with the result that when a taper piece of work is turned that has a collar or flange on it, the face of that collar or flange will be turned not at a right angle to the work axis as it should be, but at a right angle to the surface of the cone. Thus in Fig. 486 A represents the axis of a piece of work, and the slide nut having been set parallel to the work axis, the face C will be at a right angle to the surface B or axis A, but with the slide nut set at an angle to turn the cone D, the cross slide will be at an angle to A, hence the face E will be undercut as shown, and at a right angle to the surface D instead of to A A. This may be obviated by letting the cross slide be the lower one as in the English form of slide rest shown in Fig. 487, in which the upper slide is pivoted at its centre to the cross slide and may be swung at an angle thereto and secured in its adjusted position by the bolt at F. The projection at the bottom of the lower slider fits between the shears of the lathe and holds the lower slider parallel with the line of lathe centres, which causes the slide rest to cut all faces at a sight angle to the work axis whether the feed traverse slide be set to turn parallel or taper. In either case, however, there is nothing to serve as a guide to set the feed traverse slide parallel to the work axis, and this must, therefore, be done as near as may be by the eye and by taking a cut and testing its parallelism.

The rest may be set approximately true by bringing the operator's eye into such a position that the edge _a_ _a_, Fig. 488, of the slide rest come into line with the edge _b_ _b_ of the lathe shears, because that edge is parallel to the line of lathe centres, and therefore to the work axis.

Slide rests which have a slide for traversing the tool along the work to its cut are but little used in the United States, being confined to very small lathes, and then (except in the case of watchmakers' lathes whose forms of slide rest will be shown hereafter), mainly as an expedient to save expense in the cost of the lathe, it being preferred to feed the tool for the feed traverse (as the motion of the cutting tool along the work is termed) by mechanism operated from the live spindle and to be hereafter described. In England, however, slide rests are much used, a specimen construction being shown in Fig. 489. The end face A of the rest comes flush so that the tool shall be carried firmly when taking facing cuts in which solidity in the rest is of most importance. The tool is held by two clamps instead of by single tool posts, because the slide rest is employed to take heavy cuts, and when this is the case with boring tools whose cutting edges stand far out from the slide rest, a single tool post will not hold the tool sufficiently firm.

The gib _e_, Fig. 485, is sometimes placed on the front side of the slider, as in the figure, and at others on the back; when it is placed in the front the strain of the cut causes it to be compressed against the slide, and there is a strain placed upon the screws _f_ which lifts them up, whereas if placed on the other side the screws are relieved of strain, save such as is caused by the setting of the gib up.

On the other hand, the screws are easier to get at for adjustment if placed in front. When the screws _b_ of the upper gib _c_, Fig. 485, are on the right-hand side, as in that figure, there is considerable strain on the screws when a boring tool is used to stand far out, as for boring deep holes. On the other hand, however, the screws can be readily got at in this position, and may therefore be screwed up tightly to lock the upper slider firmly to the cross slide, which will be a great advantage in boring and also in facing operations. But the screws must not in this case have simple saw slot heads, such as shown on a larger scale in Fig. 490, but should have square heads to receive a wrench, and if these four screws are used, the two end ones may be set to adjust the slicing fit of the slider, while the two middle ones may be used to set the slider form on its slide when either facing or boring. The corners of the gibs as well as those of the slider and slide may with advantage be rounded so that they may not become bruised or burred, and, furthermore, the slider is strengthened, and hence less liable to spring under the pressure of a heavy cut.

A slide rest for turning spherical work is shown in Fig. 491. A is the lower slide way on which is traversed the slide B, upon which is fitted the piece C, pivoted by the bolt D; there is provided upon C a half-circle rack, shown at E, and into this rack gears a worm-wheel having journal bearing on B, and operated by the handle F. As F is rotated C would rotate on D as a centre of motion, hence the tool point would move in an arc of a circle whose radius would depend upon the distance of the tool point from D as denoted by J, which should be coincident with the line of centres of the lathe.

The slide G is constructed in the ordinary manner, but the way on which it slides should be short, so as not to come into contact with the work. If the base slide way A be capable of being traversed along the lathe shears S S by a separate motion, then the upper slide way and slide may be omitted, G and C being in one piece. It is to be noted in a rest of this kind, however, that the tool must be for the roughing cut set too far from D to an amount equal to about the depth of cut allowed to finish with, and for the finishing cut to the radius of the finished sphere in order to obtain a true sphere, because if B be operated so that D does not stand directly coincident with the line of lathe centres, the centre of motion, or of the circle described by the tool point, will not be coincident with the centre on which the work rotates, hence the work though running true would not be a true sphere but an oval. This oval would be longest in the direction parallel with the line of centres whenever the pivot D was past the line of centres, and an oval of largest diameter at the middle or largest diameter turned by the tool whenever the pivot D was on the handle H side of the line of centres. To steady C it may be provided with a circular dovetail, as shown at the end I, provision being made (by set screw or otherwise) for locking C in a fixed position when using the rest for other than spherical work.

To construct such a rest for turning curves or hollows whose outline required to be an arc of a circle, the pivot D would require to be directly beneath the tool post, which must in this case occupy a fixed position. The radius of the arc would here again be determined by the distance of the tool point from the centre of rotation of the pivot, or, what would be the same thing, from that of the tool post.

Next to the hand slide rest lathe comes the self-acting or engine lathe. These are usually provided with a feed motion for traversing the slide rest in the direction of the length of the bed, and sometimes with a self-acting cross feed, that is to say, a feed motion that will traverse the tool to or from the line of centres and at a right angle to the same.

In an engine lathe the parallelism or truth of the work depends upon the parallelism of the line of centres with the shears of the lathe, and therefore upon the truth of the shears or bed, and its alignment with the cone spindle and tail spindle, while the truth of the radial faces on the turned work depends upon the tool rest moving on the cross slide at a true right angle to the line of centres.

Fig. 492 represents an 18-inch engine (or self-acting) lathe designed by and containing the patented improvements of S. W. Putnam, of the Putnam Tool Company, of Fitchburg, Massachusetts. The lathe has an elevating slide rest self-acting feed traverse and self-acting cross feed, both feeds being operative in either direction. It has also a feed rod for the ordinary tool feeding and a lead screw for screw-cutting purposes.

Fig. 493 represents a cross-sectional view of the shears beneath the headstock; A A are the shears or bed having the raised [V]s marked V´ and V on which the headstock and tailstock rest, and V´´ and V´´´ on which the carriage slides. A and A´ are the shears connected at intervals by cross girts or webs B to stiffen them. C C are the bolts to secure the headstock to the shears. D is a bracket bolted to A´ and affording at E journal bearing for the spindle that operates the independent feed spindle. E is split at _f_ and a piece of soft wood or similar compressible material is inserted in the split. The bolt F is operated to close the split, and, therefore, to adjust the bore E to properly fit the journal of the feed spindle, and as similar means are provided in various parts of the lathe to adjust the fits of journals and bearings the advantages of the system may here be pointed out. First, then, the fit of the bearing may be adjusted by simply operating the screw, and, therefore, without either disconnecting the parts or performing any fitting operation, as by filing. Secondly, the presence of the wood prevents the ingress of dust, &c., which would cause the bearings and journals to abrade; and, thirdly, the compression of the wood causes a resistance and pressure on the adjusting screw thread, which pressure serves to lock it and prevent it from loosening back of itself, as such screws are otherwise apt to do.

As the pressure of the tool cut falls mainly on the front side of the carriage, and as the weight of the carriage itself is greatest on that side, the wear is greatest; this is counteracted by forming the front [V], marked V´´´ in figure, at a less acute angle, which gives it more wearing area and causes the rest to lower less under a given amount of wear.

The rib A´´ which is introduced to strengthen the shears against torsional strains, extends the full length of the shears.

Fig. 494 is a sectional side elevation of the headstock; A A´ represents the headstock carrying the bearing boxes B and B´, which are capable of bore closure so as to be made to accurately fit the spindle S by the construction of the front bearing B, being more clearly shown in Fig. 495; B is of composition brass, its external diameter being coned to fit the taper hole in the head; it is split through longitudinally, and is threaded at each end to receive the ring nuts C and C´. If C be loosened from contact with the radial face of A, then C´ may be screwed up, drawing B through the coned hole in A, and, therefore, causing its bore to close upon S.

At the other end of S, Fig. 496, C´´ is a ring nut for drawing the journal box B´ through _a´_ to adjust the bore of B´ to fit the journal of S, space to admit the passage of B´ being provided at _e_. D is a box nut serving to withdraw B´ or to secure it firmly in its adjusted position, and also to carry the end adjusting step E. F is a check nut to lock E in its adjusted position.

The method of preventing end motion to S is more clearly shown in Fig. 496, in which _h_ is a steel washer enveloping S, having contact with the radial face of B´ and secured in its adjusted position by the check nuts _g_, hence it prevents S from moving forward to the right. _f_ is a disk of raw hide let into E; the latter is threaded in D and is squared at the end within F to admit of the application of a wrench, hence E may be screwed in until it causes contact between the face of _f_ and the end of S, thus preventing its motion to the left. By this construction the whole adjustment laterally of S is made with the short length from _h_ to _f_, hence any difference of expansion (under varying temperature) between the spindle and the head A A´, or between the boxes and the spindle S, has no effect towards impairing the end fit of S in its bearings.

The method of adjusting the bearings to the spindle is as follows:--C´´ and C´ are slackened back by means of a "spanner wrench" inserted in the holes provided for that purpose. C and D are then screwed up, withdrawing B and B´ respectively, and leaving the journal fit too easy. C´ is then screwed up until B is closed upon the spindle sufficiently that the belt being loose on the cone pulley, the latter moved by the hand placed upon the smallest step of the cone can just detect that there is contact between the bore of B and the spindle, then, while still moving the cone, turn C´ back very slowly and a very little, the object being to relieve the bore of B from pressure against S. C may then be screwed up, firmly locking B in its adjusted position. C´´ may then be operated to adjust B´ in a similar manner, and D screwed up to lock it in its adjusted position. Before, however, screwing up D it is better to remove F and release E from pressure against _f_, adjusting the end pressure of E after D has been screwed home against A´.

To prevent B and B´ from rotating in the head when the ring nuts are operated, each is provided with a pin, _q_, grooves _c_ and _c´_ permitting of the lateral movement of B and B´ for adjustment. The boxes B, B´ admit of being rotated in their sockets in A and A´ so as to assume different positions, the pins _q_ and _q´_ being removable from one to another of a series of holes in the boxes B, B´ when it is desired to partly rotate those boxes. The tops of the boxes are provided with oil holes, and the oil ways shown at _r_, _s_ being the oil groove through the head and _a_ simply a stopper to prevent the ingress of dust, &c.

The thread on S at Z, Fig. 494, is to receive and drive the face plates, chucks, &c., which are bored and threaded to fit over Z. To cause the radial faces of such face plates or chucks to run true, there is provided the plain cylindrical part _l_, to which the bore in the hub of the face plate or chuck is an accurate fit when the radial face of that hub meets the radial face _m_.

Referring again to Fig. 494, G´ is the pinion to drive the back gear while G receives motion from the back-gear pinion. The object of the back gear is to reduce the speed of rotation of S and to enable it to drive a heavier cut, which is accomplished as follows:--G´ is secured within the end K of the cone and is free to rotate with the cone upon S; at the other end the cone is secured to M, which is free to rotate upon S so far as its bore is concerned. G is fixed upon S and hence rotates at all times with it; but G may be locked to or released from M as follows:--

In G is a radial slot through which passes a bolt I provided with a cap nut H, in M is an annular groove J. When I is lifted its head passes into a recess in M, then H is screwed up and G is locked to M. This is the position of I when the back gear is not in use, the motion of the cone being communicated to S through I. But if H be loosened and I be moved inwards towards S, the head of I passes into the annular groove J, and the cone is free to rotate upon S while the latter and G remain stationary unless the back gear is put into operation. In this latter case the pinion G´ rotating with the cone drives the large gear of the back gear and the small pinion of the latter drives G, whose speed of rotation is reduced by reason of the relative proportions of the gear wheels.

In this case it is obvious that since the pulley rotates upon the spindle it requires lubrication, which is accomplished through the oil hole tubes L.

The means of giving motion to the feed spindle and lead screw are as follows:--N, Fig. 494, is a pinion fast upon S and operating the gear O, which is fast upon the spindle P, having journal bearing in a stem in A´ and also at G´´. P drives the three-stepped cone R, which is connected by belt to a similar cone fast upon the independent feed spindle. The seat for the driving gear of the change wheels for the lead screw is on P at V. To provide ample bearing surface for P in A´ the bush or sleeve shown is employed, but this sleeve also serves to pivot the swing frame W which carries the studs for the change wheels that go between the wheel on V and that on the lead screw; _x_ _y_ are simply oil holes to lubricate P in its bearings.

To provide a wider range of tool feed than that obtainable by the steps on the feed cones, as R, they are provided at their ends with seats for change wheels, the swing frame W carrying the intermediate wheels for transmitting motion from V to a similar seat on the cone on the feed spindle.

Fig. 497 represents the tailstock (or tailblock as it is sometimes termed), shown in section. A represents the base which slides upon the raised [V]s on the bed and carries the upper part B, in which slides the tail spindle C, which is operated longitudinally by the tail screw D, having journal bearing in E, and threaded through the nut F which is fast in C. The hand wheel G is for rotating D, whose thread operating in the nut F, causes C to slide within B in a direction determined by the direction of rotation of G. To lock C in its adjusted position the handled nut H is employed in connection with the bolt I, which is shown in dotted lines; C is split as shown by the dotted lines at _f_; J is the dead centre fitting accurately into a conical hole in C. When it is required to remove J from C the wheel G is operated to withdraw C entirely within B, and the end _d_ of D meets the end _e_ of J and forces J from the coned hole in C.

The method of securing the tailstock to the shears or releasing it from the same is as follows. A vertical prolongation of B affords at B´´ a bearing surface for the nut-handle L and washer M. K is a bolt threaded into L passing through M, B´´ and N, the latter of which it carries. N spans the shears beneath the two [V]s on which the tailstock slides. Moving or rather partly rotating the handle L in the necessary direction lifts K and causes N to rise, and grip the shears beneath, while the pressure of M on B´´ causes B to grip A and the latter to grip the raised [V]s on the shears. If L be rotated in the opposite direction it will cause N to fall, leaving A free to slide along the shears. To prevent N from partly rotating when free, its ends are shaped to fit loosely between the shears as shown at _n_.

To give to N sufficient rise and fall to enable it to grip or fall entirely free from the shears with the small amount of rotary motion which the handle-lever L is enabled from its position to have, the following device is provided. M is a washer interposed between L and B´´. This washer has upon it steps of different thickness as shown at M and _m_, the two thicknesses being formed by an incline as shown. The face of L has, as shown, similar steps; now as shown in the cut the step _l_ on lever L meets the steps _m_ of the washer, the handle having receded to the limit of its motion. The bolt K then has fallen to the amount due to unscrewing the threaded or nut end of L, and also to the amount of the difference of thickness at M and at _m_ of the washer, the plate N being clear of the lathe-shears. But suppose the handle L be pulled towards the operator, then the surface _l_ passing from a thin section on to a thick one as M of the washer, will lift the bolt K, causing N to meet the under surface of the shears, and then the motion of L continuing the pressure of the thread will bind or lock N to the bed.

The surface A´ in Fig. 497 affords a shelf or table whereon tools, &c., may be placed instead of lying on the lathe bed, where they may cause or receive damage.

Fig. 498 represents an end view of the tailstock viewed from the dead centre end, the same letters of reference applying to like parts that are shown in Fig. 497. The split at _f_ is here shown to be filled with a piece of soft wood which prevents the ingress of dust, &c. At _d_ is a cup or receptacle for oil, _e_ being a stopper, having attached to it a wire pin flattened and of barb shape at the end, the object being to cause the wire to withdraw from the cup a drop of oil to lubricate the dead centre and centre in the work. The proximity of _e_ to the dead centre makes this a great convenience, while the device uses much less oil than would be used by an oil can.

The method of setting over the upper part B to enable the turning of the diameter of work conical or taper instead of parallel is shown in Fig. 498: P and P´ are square-headed screws threaded into the walls of A and meeting at their ends the surface of B´. In A there is at _a_ a wide groove or way, and on B there is at _b_ a projection fitting into the way _a_ so as to guide B when it slides across A, as it will when P is unscrewed in A and P´ is screwed into A. This operation is termed setting over the tailstock, and its effect is as follows:--Suppose it be required to turn a piece of work of smaller diameter at the end which runs on the dead centre, then, by operating the screw P towards the front of the lathe (or to the left as shown in the cut) and screwing P´ farther into A, the end of P´ will meet the surface of B´, causing B´ to move over, and the centre of the dead centre J (which is the axis of rotation of the work at that end) will be nearer to the point of the cutting tool. Or suppose the work requires to be turned a taper having its largest diameter at the end running on the dead centre, then P´ would be unscrewed and P screwed farther into A, carrying B farther towards the back of the lathe.

The [V] grooves Q and Q´ fit upon the inner raised [V]s shown at V, V´ in Fig. 499.

Fig. 499 is a side view of the slide rest for holding and traversing the cutting tool. A represents the carriage resting upon the raised [V]s marked V´´ and V´´´ and prevented from lifting by its own weight, and in front also by the gib _a_ secured to A by the bolt _b_ and having contact at _c_ with the shears. A carries at _d_ a pivot for the cross slide B and at _e_ a ball pivot for the cross slide elevating screw C. This screw is threaded through the end of B so that by operating it that end of B may be raised or lowered to adjust the height of the cutting tool point to suit the work. To steady B there is provided (in addition to the pivots at _d_) on A two lugs _f_, between the vertical surfaces of which B is a close working fit. The upper surface of B is provided with a [V]-slide-way _g_, to which is fitted the tool rest D (the construction being more clearly shown in Fig. 500).

The means for traversing D along the slide _g_ on B is as follows:--

A nut _i_ is secured to D by the screw bolt _j_, and threaded through the nut _i_ is the cross-feed screw E, which has journal bearing in the piece _k_, which is screwed into the end face of B; there is a collar on E which meets the inner end of _k_, and the handle F being secured by nut to that end of E its radial face forms a shoulder at _m_ which with the collar prevents any end motion of E, so that when F is rotated E rotates and winds through the nut _i_ which moves D along B.

An end view of A, B, and D is shown in Fig. 500, in which the letters of reference correspond to those in Fig. 499. B´ and B´´ are the projections that pass into A and receive the pivoting screws _d_ and _d_. To adjust the fit and take up any wear that may ensue on the slide _g_, on B and on the corresponding surface on D, the piece _n_ is provided, being set up by the adjusting screws O.

To adjust the fit and take up the wear at the pivots _d_ they are made slightly taper, fitting into correspondingly taper holes in B.

The dotted circle T´, represents a pinion fast upon the cross-feed screw (E, Fig. 499); the similar circles T and S´´ also represent pinions, the three composing a part of the method of providing an automatic or self-acting cross feed or cross traverse to D by rotating it through a gear-wheel motion derived from the rotation of the independent feed spindle, as is described with reference to Fig. 501.

_m_ in Fig. 500 represents a cavity or pocket to receive wool, cotton or other elastic or fibrous material to be saturated with oil and thus lubricate the raised [V]s while keeping dirt from passing between the rest and the [V]s. The shape of these pockets is such as to enable them to hold the cotton with a slight degree of pressure against the slides, thus insuring contact between them.

The mechanical devices for giving to the carriage a self-acting traverse in either direction along the bed, so as to feed the tool automatically to its cut, and for giving to the tool rest (D, Fig. 499) traverse motion so as to feed the tool to or from the line of centres along the cross slide, are shown in Fig. 501, which presents two views of the feed table or apron. The lower view supposes the feed table to be detached from the carriage and turned around so as to present a side elevation of the mechanism. The upper view is a plan of the same with two pinions (N and N´), omitted. A represents the part of the lathe carriage shown at A in Fig. 500. It has two bolts _p_ and _p´_, which secure the apron G, Fig. 501, to A. At H is the independent feed spindle or feed rod operated by belt from the cone pulley R, Fig. 494, or by a gear on stud P at V. H is carried in bearings fixed to each end of the lathe shears or bed, both of these bearings being seen in Fig. 492. H is also provided with a bearing fixed on the feed apron as seen in Fig. 501, and is splined as shown at _h_. At I is a bracket fast upon the apron G and affording journal bearing to J, which is a bevel pinion having a hub which has journal bearing in the bracket I. The fit of the bearing to the journal is here again adjusted by a split in the bearing with a screw passing through the split and threaded in the lower half (similar to the construction of D in Fig. 493); J is bored to receive H, and is driven by means of a feather projecting into the spline _h_. When therefore, the carriage A is moved it carries with it the apron G, and this carries the bracket I holding the bevel pinion J, which is in gear with the bevel-wheel K, and therefore operates it when H has rotary motion. At the back of K, and in one piece with it, is a pinion K´, both being carried upon the stud L; pivoted upon this same stud is a plate lever M, carrying two pinions N and N´ in gear together, but N only is in gear with K´, hence K´ drives N and N drives N´. Now in the position shown neither N or N´ is in gear with the gear-wheel O, but either of them may be placed in gear with it by means of the following construction:--

At the upper end of M there is provided a handle stud M´ passing through the slot M´´ in G. Screwing up this stud locks M fast by binding it against the surface of G. Suppose, then, M´ to be unscrewed, then if it be moved to the right in the slot M´´, N will be brought into gear with O and the motion will be transmitted in the direction of the arrows, and screwing up N would retain the gear in that position. But suppose that instead of moving M´ to the right it be moved to the left, then N´ will be brought into gear with O and the direction of rotation of O will be reversed.

Thus, then, O may be made to remain stationary or to rotate in either direction according to the position of M´ in the slot M´´, and this position may be regulated at will.

The gear O contains in its radial face a conical recess, and upon the same stud or pin (P) upon which O is pivoted, there is fixed the disk P´, which is in one piece with the pinion P´´; the edge of P´ is coned to fit the recess in the wheel O, so that if the stud P is operated to force the disk P´ into the coned recess in O the motion of wheel O will be communicated to disk P´, by reason of the friction between their two coned surfaces. Or if P be operated to force the coned edge of the disk out of contact with the coned bore or recess in gear O, then O will rotate while P´ and P´´ will remain stationary. Suppose the coned surfaces to be brought (by operating _x_) into contact and P´ to rotate with O, then P´´ being in gear with wheel Q will cause it to rotate. Now Q is fast to the pinion Q´, hence it will also rotate, and being in contact with the rack which is fixed along the shears of the lathe and a section of which is shown in the cut, the whole feed table or apron will be made to traverse along the lathe shears.

The direction in which this traverse will take place depends upon the adjusted position of M´ in M´´, or in other words upon whether N or N´ be the pinion placed in gear with O. As shown in the cut neither of them is in gear, and motion from H would be communicated to N and N´ and would there cease; but if M´ be raised in the slot M´´, N would drive O, and supposing P´ to be held to O, the motion of all the gears would be as denoted by the arrows, and the lathe carriage A would traverse along the lathe bed in the direction of arrow Q´´. But if N´ be made to drive O all the motions would be in the opposite directions. The self-acting feed motion thus described is obviously employed to feed the cutting tool, being too slow in its operation for use to simply move the carriage from one part of the lathe bed to another; means for this purpose or for feeding the carriage and cutting tool by hand are provided as follows:--R is a pinion in gear with Q and fast upon the stud R´, which is operated by the handle R´´. The motion of R´´ passes from R to Q and Q´ which is in gear with the rack. But Q´ being in gear with P´´ the latter also rotates, motion ceasing at this point because the cone on P´ is not in contact with the coned recess in O. When, however, P´ and O are in contact and in motion, that motion is transmitted to R´´, which cannot then be operated by hand.

It is often necessary when operating the cross feed to lock the carriage upon the lathe bed so that it shall not move and alter the depth of the tool-cut on the radial face of the work. One method of doing this is to throw off the belt that operates the feed spindle H, place N in gear with O and P´ in contact with O, so that the transverse feed motion will be in action, and then pull by hand the cone pulley driving H, thus feeding the tool to its necessary depth of cut. The objection to this method, however, is that when the operator is at the end of the lathe, operating the feed cone by hand he cannot see the tool and can but guess how deep a cut he has put on. To overcome this difficulty a brake is provided to the pinion R as follows:--

The brake whose handle is shown at V has a hub V´ enveloping the hub R´´´ which affords journal bearing to the stud R´. In the bore of this hub V´ is an eccentric groove, and in R´´´ is a pin projecting into the eccentric groove and meeting at its other end the surface of the stud R´. When, therefore, V is swung in the required direction (to the left as presented in the cut), the cam groove in V´ forces _r_ inwards, gripping it and preventing it from moving, and hence the movement of R which also locks Q and Q´.

It remains now to describe the method of giving rotary motion to the cross-feed screw E (Fig. 499) so as to enable it to self-act in either direction. S is a lever pivoted upon the hub of O and carrying at one end the pinion S´´, while at the other end is a stud S´ passing through a slot in G. The pinion S´´ is in gear with O and would therefore receive rotary motion from it and communicate such motion to pinion T, which in turn imparts rotary motion to T´. Now T´ is fast upon the cross-feed screw as shown in Fig. 499 and the cross-feed screw E in that figure would by reason of the nut _i_ in figure cause the tool rest D to traverse along the cross-slide in a direction depending upon the direction of motion of T´, which may be governed as follows:--

If S´ be moved to the left S´´ will be out of gear with T and the cross-feed screw may be operated by the handle (F, Fig. 499). If S´ be in the position shown in cut and M´´ also in the position there shown (Fig. 501), operating the feed screw by its handle would cause its pinion T´ to operate T, S´´, and O; hence S´ should always be placed to disconnect S´´ from T when the cross-feed screw is to be operated by hand, and S´ operated to connect them only when the self-acting cross feed is to operate. In this way when the cross feed is operated by hand T´ and T will be the only gears having motion. It has been shown that the direction of motion of O is governed by the position of M´, or in other words, is governed by which of the two pinions N or N´ operates, and as O drives S´´ its motion, and therefore that of T´, is reversible by operating M´.

The construction of S´ is as follows:--Within the apron as shown in the side elevation it consists of what may be described as a crank, its pin being at _t_; in the feed table is a slot through which the shaft of the crank passes; _s_ is a handle for operating the crank. By rotating _s_ the end S´ of S is caused to swing, the crank journal moving in the slot to accommodate the motion and permit S to swing on its centre.

The device for forcing the cone disk P´ into contact with or releasing it from O is as follows:--The stud P is fast at the other end in P´ and has a collar at _b_; the face of this collar forms one radial face, and the nut W affords the other radial face, preventing end motion to _x_ without moving P endwise. If _x_ be rotated its thread at _x´_ causes it to move laterally, carrying P with it, and P being fast to P´ also moves it laterally. P´ is maintained from end motion by a groove at O´ in which the end of a screw _a_ projects, _a_ screwing through W and into the groove O´.