Lathe Shears or Beds.—The forms of the shears and beds may be classified as follows.

The term shear is generally applied when the lathe is provided with legs, while the term bed is used when there are no legs; it may be noted, however, that by some workmen the two terms of shear and bed are used indiscriminately.

The forms of shears in use on common lathes are, in the United States, the raised V, the flat shear and the shear, with the edge at an angle of 90° or with parallel edges. In England and on the continent of Europe, the flat shear is almost exclusively employed.

Referring to the raised V it possesses an important advantage in that, first, the slide rest does not get loosely guided from the wear; and second, the wear is in the direction that least affects the diameter of the work.

In Fig. 621, for example, is a section of a lathe shear, with a slide rest shown in place, and it will be observed that the wear of the V upon the lathe bed, and of the V-groove in the slide rest, will cause the rest to fall in the direction of arrow a, and that a given amount of motion in that direction will have less effect in altering the diameter than it would in any other direction. This is shown on the right hand of the figure as follows: Suppose the cutting point of the tool is at a, and the work will be of the diameter shown by the full circle in the figure. If we suppose the tool point to drop down to f, the work would be turned to the diameter denoted by dotted arc g, while if the tool were moved outwards from a to c the work would be turned to the diameter e. Now since f and c are equidistant from the point a, therefore the difference in the diameters of e and g represents the difference of effect between the wear letting the rest merely fall, or moving it outwards, and it follows that, as already stated, the diameter of the work is less affected by a given amount of wear, when this wear is in the direction of a, than when it is in the direction of b. When the carriage is held down by a weight as is shown in Figs. 577 and 578, there is therefore no lost motion or play in the carriage, which therefore moves steadily upon the shears, unless the pressure of the cut is sufficient in amount, and also in a direction to lift the carriage (as it is in the case of boring with boring tools); but to enable the carriage to remain firm upon the shears under all conditions, it is necessary to provide means to hold it down upon the Vs, which is done by means of gibs g, g, which are secured to the carriage, and fit against the bottom of the bed flange as shown.

Now since lathes are generally used much more frequently on short than on long work, therefore the carriage traverses one part of the shears more than another, and the Vs wear more at the part most traversed, and it follows that if gibs g are set to slide properly at some parts they will not be properly set at another or other parts of the length of the shears; hence the carriage will in some parts have liberty to move from the bed, there being nothing but the weight of the carriage, &c., to hold it down to the Vs. Now, the wear in the direction of a acts directly to cause this inequality of gib fit, whereas that in the direction of b does so to a less extent, as will appear hereafter.

Meantime it may be noted that when the carriage is held down by a suspended weight the shears cannot be provided with cross girts, and are therefore less rigid and more subject to torsion under the strain of the cut; furthermore the amount of the weight must be sufficient to hold the carriage down under the maximum of cut, and this weight acts continuously to wear the Vs, whether the carriage is under cutting duty or not, but the advantage of keeping the carriage firmly down upon the Vs is sufficiently great to cause many to prefer the weighted carriage for light work driven between the lathe centres.

Fig. 622 represents the flat shear, the edges being at an angle and the fit of the carriage to the shears being adjusted by the gibs at a a, which are set up by bolts c c and d d. In this case there is a large amount of wearing surface at b b, to prevent the fall of the carriage c, but the amount of end motion (in the direction of b, Fig. 621), permitted to the carriage by reason of the wear of the gibs and shear edges, is greater than the amount of the wear because of the edges being at an angle. It is true that the amount of fall of the carriage on the raised V is also (on account of the angle of the V) greater than the actual amount of the wear, but the effect upon the work diameter is in this case much greater, as will be readily understood from what has already been said. The wearing surface of the raised V may obviously be increased by providing broader Vs, or two Vs instead of having four. This would tend to keep the lathe in line, because the wear due to moving the tailblock would act upon those parts of the shear length that are less acted upon by the carriage, and since the front journal and bearing of the live spindle wear the most, the alignment of the lathe centres would be more nearly preserved.

Fig. 623 represents another form of parallel edged shears in which the fit of the carriage to the shears is effected at the front end only, the other or back edge being clear of contact with the carriage, but provided with a gib to prevent the carriage from lifting. This allows for any difference in expansion and contraction between the carriage and the shears, while maintaining the fit of the carriage to the bed.

A modification of this form (both these forms being taken from “Mechanics”) is shown in Fig. 624, in which the underneath side of the front edge is beveled so that but one row of screws is required to effect the adjustment.

Fig. 625 represents a form of bed in which the fit adjustment is also made at the front end only of the bed, and there is a flange or slip at a, which receives the thrust outwards of the carriage; and a similar design, but with a bevelled edge, is shown in Fig. 626.

In Fig. 627 is shown a lathe shear with parallel edges, the fit being adjusted by a single gib d, set up by set-screws s. In this case the carriage will fall or move endwise, to an amount equal to whatever the amount of the wear may be, and no more, but it may be observed that in all the forms that admit of wear endways (that is to say in the direction of b in Fig. 621), the straightness of the shears is impaired in proportion as its edges are more worn at one part than at another.

A compromise between the flat and the raised V-shear is shown in Fig. 628, there being a V-guide on one side only, as at j. When the carriage is moved by mechanism on the front side of the lathe, and close to the V, this plan may be used, but if the feed screw or other mechanism for traversing the carriage is within the two shears, the carriage should be guided at each end, or if the operating mechanism is at the back of the lathe, the carriage should be guided at the back end, if not at both ends.

In flat shear lathes the tailstock is fitted between the inside edges of the two shears, and the alignment of the tailstock depends upon maintaining a proper fit notwithstanding the wear that will naturally take place in time. The inside edges of the shears are sometimes tapered; this taper makes it much easier to obtain a correct fit of the tailstock to the shears, but at the same time more hard to move the tailstock along the bed. To remedy this difficulty, rollers are sometimes mounted upon eccentrics having journal bearing in the tailstock, so that by operating these eccentrics one half a turn, the rollers will be brought down upon the upper face of the shears, lifting the tailstock and enabling it to be easily moved along the bed to its required position.

In many of the watchmakers’ lathes the outer edges are beveled off as in Fig. 629, the bearing surfaces being on the faces b as well as on the edges a. As a result, edges a are relieved of weight, and therefore to some extent of wear also, and whatever wear faces b have helps the fit at a a.

In the Barnes lathe, as in several other forms in which the lathe is made (as, for example, in screw-making lathes) the form of bed in Fig. 630 is employed. The tailblock may rest on the surfaces a, a′, b, c, d, and e, or as in the Barnes lathe the tailstock may fit to angles a b, but not to e d, while the carriage fits to b e, and c d, but not to a, the intention being to equalize the wear as much as possible.

The shears of lathes require to be as rigid as possible, because the pressure of the cut, as well as the weight of the carriage, slide rest, and tailstock, and of the work, tends to bend and twist them.

The pressure of the dead centre against the end of the work considered individually, is in a direction to bend the lathe shears upward, but the weight of the work itself acts in an opposite direction.

The strain due to the cut falls in a direction variable with the shape of the cutting tool, but mainly in a direction towards the operator, and, therefore, tending to twist the shears. To resist these strains, lathe shears are usually given the I form shown in the cuts.

Figs. 631 and 632 represent the ribbing in the Putnam Tool Company’s lathe; a middle rib running the entire length, which greatly stiffens it.

The legs supporting lathe shears are, in lathes of ordinary length, placed at each end of the bed, so that the weight of the two heads, that of the work, and that of the carriage and slide rest, as well as the downward pressure of the cut, act combined to cause it to deflect or bend. It is necessary, therefore, in long beds to provide intermediate resting or supporting points to prevent this deflection.

Professor Sweet has pointed out that a lathe shears will be more truly supported on three than on four resting points, if the foundation on which the legs rest do not remain permanently level, and in lathes designed by him has given the right-hand end of the shears a single supporting point, as shown at a in Fig. 633.

J. Richards in an article in “Engineering,” has pointed out also that, when the lathe legs rest upon a floor that is liable from moving loads upon it to move its level, it is preferable that the legs be shaped as in Fig. 634, being narrowest at the foot, whereas when upon a permanent foundation, in which the foundation is intended to impart rigidity to the legs, they should be broader at the base, as in Fig. 635.

The rack on a lathe bed should be a cut one, and not simply a cast one, because when a cutting tool is running up to a corner as against a radial face, the self-acting motion must be stopped and the tool fed into the corner by hand. As a very delicate tool movement is required to cut the corner out just square, it should be capable of easy and steady movement, but in the case of cast racks, the rest will, from defects in the rack teeth, move in little jumps, especially if the pitch of the teeth be coarse. On the other hand it is difficult to cast fine pitches of teeth perfectly, hence the racks as well as the gear teeth should be cut gear and of fine pitch.

The tailblock of a lathe should be capable of easy motion for adjustment along the shears, or bed of the lathe, and readily fixable in its adjusted position. The design should be such as to hold the axial line of its spindle true with the axial line of the live spindle. If the lathe bed has raised Vs there are usually provided two special Vs for the tailblock to slide on, the slide rest carriage sliding on two separate ones. In this case the truth of the axial line of the tail spindle depends upon the truth of the Vs.

If the lathe bed is provided with ways having a flat surface, as was shown in Fig. 622, the surfaces of the edges and of the projection are apt in time to wear, permitting an amount of play which gives room for the tailblock to move out of line. To obviate this, various methods are resorted to, an example being given in the Sellers lathe, Fig. 518.

In wood turners’ lathes, where tools are often used in place of the dead centre, and in which a good deal of boring is done by such use of the tail spindle, it is not unusual to provide a device for the rapid motion of that spindle. Such a device is shown in Fig. 636; it consists of an arm a to receive the end c of the lever b, c being pivoted to a. The spindle is provided with an eye at e, the wheel w is removed and a pin passed through d and e, so that by operating the handle the spindle can be traversed in and out without any rotary motion of the screw.

When the tailblock of a lathe fits between the edges of the shears, instead of upon raised Vs, it is sometimes the practice to give them a slight taper fitting accurately a corresponding taper on the edges of the shears. This enables the obtenance of a very good fit between the surfaces, giving an increased area of contact, because the surfaces can be filed on their bearing marks to fit them together; but this taper is apt to cause the tailstock to fit so tightly between the shears as to render it difficult to move it along them, and in any event the friction is apt to cause the fit to be destroyed from the wear. An excellent method of obviating these difficulties is by the employment of rollers, such as shown at r in Figs. 637 and 638, which represent the tailstock of the Putnam Tool Company’s lathe. In some cases such rollers are carried on eccentric shafts so that they may be operated to lift the tailstock from the bed when moving it.

A very ready method of securing or releasing a small tailstock to a lathe shears is shown applied to a wood turner’s hand rest in Fig. 639, in which a a represents the lathe shears, b the hand rest, c the fastening bolt, d a piece hinged at each end and having through its centre a hole to receive the fastening bolt, and a counter-sink or recess to receive the nut and prevent it unscrewing. e represents a hinged plate, and f a lever, having a cam at its pivoted end. A slot for the fastening bolt to pass through is provided in the plate e. In this arrangement a very moderate amount of force applied to bring up the cam lever will cause the plate d to be pressed down, carrying with it the nut, and binding the tailstock or the tool rest, as the case may be, with sufficient force for a small lathe.

When a piece of work is driven between the lathe centres, the weight of the work tends to deflect or bend down the tail spindle. The pressure of the cut has also to be resisted by the tail spindle, but this pressure is variable in direction, according to the shape of the tool and the direction of the feed; usually it is laterally towards the operator and upwards. In any event, however, the spindle requires locking in its adjusted position, so as to keep it steady. The pressure on the conical point of the dead centre is in a direction to cause the tail screw to unwind, unless it be a left-hand thread, as is sometimes the case.

If the spindle and the bore in which it operates have worn, the resulting looseness affords facility for the spindle to move in the bore as the pressure of the cut varies, especially when the spindle is far out from the tailstock.

Now, in locking the tail spindle to obviate these difficulties, it is desirable that the locking device shall hold that spindle axially true with the live spindle of the lathe, notwithstanding any wear that may have taken place. The spindle is released from the pressure of the locking device whenever it is adjusted to the work, whether the cut be proceeding or not. Hence, the wear takes place on the bottom of the spindle and of the hole, wear only ensuing on the top of the spindle and bore when the spindle is operated under a slight locking pressure, while the cut is proceeding in order to take up the looseness that may have arisen from wear in the work centres.

In all cases the feed of the cut should be stopped while the centre is adjusted, so as to relieve the spindle and bore from undue wear; but most workmen pay little heed to this; hence the wear ensues, being, as already stated, mainly at the bottom. It is obvious, then, that, if the spindle is to be locked to the side of the bore on which it slides, it will be held most truly in line if it be locked to that side which has suffered least from wear, and this has been shown to be at the top.

The methods usually employed to effect this locking are as follows:—In Fig. 640, s is the tail spindle, b part of the tailblock in section, r a ring-bolt, and h a handled nut. Screwing up the nut h causes r to clamp s to the upper part of the bore of b; while releasing h leaves s free to slide. There are three objections to this plan. The ring r tends to spring or bend s. The weight of r tends to produce wear upon the top of the spindle, and the spindle is not gripped so near to its dead centre end as it might be. If s is a close fit in b the pressure of r could not spring or bend s; but, so soon as wear has taken place, s becomes simply suspended at r, having the pressure of r, and the weight of the work tending to bend it. Another locking device is shown in Fig. 641. It consists of a shoe placed beneath s, and a wedge-bolt beneath it, operated by the handled nut c. Here the pressure is again in a direction to lift s, as denoted by the arrow; but when the wedge w is released the shoe falls away from s, hence the locking device produces no wear upon s. This device may be placed nearer to the end of b, since the wedge may pass through the front leg of the tailstock instead of to the right of it, as in Fig. 640. But s is still suspended from the point of contact of the shoe, and the weight of the work still bends it as much as its play in b will permit.

Another clamping device is shown in Fig. 642. In this the cylindrical part b of the tailblock is split on one side, and is provided with two lugs. A handled screw passes through the upper lug, and is threaded into the lower one, so that by operating the handle c, the bore may be closed, so as to grip s, or opened to relieve it. This possesses the advantages: First, that it will cause s to be gripped most firmly at the end of b, and give a longer length of bearing of b upon s; and, secondly, that it will grip s top and bottom, and, therefore, prevent its springing from the weight of the work. But, on the other hand, b will close mainly on the side of the split, as denoted by the dotted half-circle, and therefore tend to throw s somewhat in the direction of the arrow, which it will do to an amount answerable to the amount of looseness of s in b. In the Pratt and Whitney lathes this device is somewhat modified, as is shown in Fig. 643. A stud e screws into the lower lug d, having a collar at e let into the upper lug, with a square extending above the upper lug so that the stud may be screwed into d, exerting sufficient pressure to close the bore of b to a neat working fit to the spindle. The handled nut, when screwed up, causes b to grip the spindle firmly; but when released, leaves the spindle a neat working fit and not loose to the amount of the play; hence, the locking device may be released, and the centre adjusted to take up the wear in the work centres while the cut is proceeding, without any movement of the spindle in b, because there is no play between the spindle and b.

In the design shown in Fig. 644, the end b of the tailblock is threaded and is provided with a handled cap nut a a. In the end of the tailblock where the spindle emerges, is provided a cone, and into this cone fits a wedge-shaped ring, as shown. This ring is split quite through on one side, while there are two other slots nearly but not quite splitting the wedge-ring. When the handle c is pulled towards the operator it screws a up on the end b, and forces the wedge-ring up in the conical bore in b. From the split the ring closes upon the spindle s, and grips it. Now, as the ring is weakened by slots in two places besides the split, it closes more nearly cylindrically true than if it had only a split, there being three points where the ring can spring when closing upon s; and from the cone being axially true with the live spindle of the lathe, s is held axially true, notwithstanding any wear of the spindle, because the locking device, being at the extreme end of b, is as near to the dead centre as it is possible to get it; and, furthermore, when c is operated for the release, the wedge-ring opens clear of s, so that s does not touch it when moved laterally. The wear of the bore of b has, therefore, no effect to throw s out of line, nor has the gripping device any tendency to bend or spring s, while the latter is held as close to the work as possible; hence the weight of the work has less influence in bending it. The pitch of the thread and the degree of cone are so proportioned that less than one-quarter rotation of a will suffice to grip or release s, the handle c being so placed on a as to be about vertical when the split ring binds s; hence c is always in a convenient position for the hand to grasp.

In this case, however, the spindle being locked at the extreme end of the hole, there is more liability of the other end moving from the pressure of the cut, or from the weight of the work; hence it would seem desirable that a tail spindle should be locked in two places; one at the dead centre end of the hole, and the other as near the actuating wheel, or handle, as possible, and also that each device should either hold it central to the original bore, notwithstanding the wear, an end that is attained in the Sellers lathes already described.

Slide rests for self-acting or engine lathes are divided into seven kinds, termed respectively as follows: simple, or single, elevating, weighted, gibbed, compound, duplex, and duplex compound. A simple, or single, slide rest contains a carriage and one cross slide, as in Fig. 621. An elevating slide rest is one capable of elevation at one end to adjust the cutting tool height, as in Fig. 499. A weighted slide rest is one held to the shears by a weight, as in Fig. 577. A gibbed slide rest is held to the shears by gibs, as in Fig. 621. A compound slide rest has above the cross slide, a second slide carrying the tool holder, this second slide pivoting to stand at any required angle, as in Fig. 505. A duplex slide rest has two rests on the same cross slide, and in a compound duplex both these two rests are compound, as in Fig. 511. The rest shown on the Putnam lathe in Figs. 492 and 499, is thus an elevating gibbed single rest.

Testing a Lathe.—To test a lathe to find if its live and dead spindles are axially in line one with the other and with the guides on the lathe bed, the following methods may be employed in addition to those referred to under the heading of Erecting.

To test if the live spindle is true with the bed or shear guides, a piece such as in Fig. 645 may be turned up between the lathe centres, the end a fitting into the live spindle in place of the live centre, and the collars b c being turned to an equal diameter, and the end face d squared off true. The end a must then be placed in the lathe in place of the live centre, the dead centre being removed from contact with the work; with the lathe at rest a tool point may be set to just touch collar c, and if when the carriage is moved to feed the tool past collar b, the tool draws a line along it of equal depth to that it drew along c, the live head is true; the dead centre may then be moved up to engage the work end d, and the lathe must be revolved so that (the tool not having been moved at all by the cross-feed screw) the tool may be traversed back to draw another line along c, and if all three lines are of equal depth the lathe is true. The tool should be fine pointed and set so as to mark as fine a line as possible.

Another method is to turn up two discs, such as in Fig. 646, their stems a and b fitting in place of the live and dead centres. One of these discs is put in the place of the live, and the other in that of the dead centre, and if then the lathe tailstock be set up so that the face of b meets that of a, their coincidence will denote the truth of the live and dead spindles. The faces of the discs may be recessed to save work and to meet at their edges only, but their diameters must be equal. If the discs come one higher than the other, as in Fig. 647, the centres are of unequal height. If the faces meet at the top and are open at the bottom, as in Fig. 648, it shows that the back bearing of the live spindle is too high, or that the tail spindle is too low at the dead centre end. If the discs, when viewed from above, come as in Fig. 649, it is proof that either the live spindle or the tail spindle does not stand true with the lathe shears. If the disc faces come so nearly fair that it is difficult to see if they are in contact all around, four pieces of thin paper may be placed equidistant between them, and the grip upon them tested by pulling.

If the tailstock has been set over to turn taper and it is required to set it back to turn parallel again, place a long rod (that has been accurately centred and centre-drilled) between the lathe centres, and turn up one end for a distance of an inch or two.

Then turn it end for end in the lathe and let it run a few moments so that the work centre, running on the dead centre of the lathe, may wear to a proper bed or fit to the lathe centre, and then turn up a similar length at the dead centre end, taking two cuts, the last a fine finishing cut taken with a sharp tool, and feeding the finishing cut from left to right, so that it will be clear of the work end when the cut is finished. Without moving the cross-feed screw of the lathe after the finishing cut is set, take the bar out of the lathe and wind the slide rest carriage, so that the turning tool will stand close to the live centre. Place the bar of iron again in the lathe, with the turned end next to the live centre, and move the lathe carriage, so that the tool is on the turned end of the bar.

Rotate the bar by hand, and if the tool just touches the work without taking a cut the line of centres is parallel with the ways. If there is space between the tool point and the turned end of the bar, the tailstock requires setting over towards the back of the lathe, while if the tool takes a cut the tailstock requires to be set over towards the operator. If a bar is at hand that is known to be true, a pointed tool may be adjusted to just make a mark on the end of the bar when the slide rest is traversed. On the bar being reversed, the tool should leave, when traversed along the bar, a similar mark on the bar.

To test the workmanship of the back head or tailstock, place the forefinger on the spindle close to the hub whence it emerges, and observe how much the hand wheel can be moved without moving the spindle; this will show how much, if any, lost motion there is between the screw and the nut in the spindle. Next wind the back spindle about three quarters of its length out of the tailstock, take hold of the dead centre and pull it back and forth laterally, when an imperfect fit between the spindle and the hole in which it slides will be shown by the lateral motion of the dead centre. Wind the dead centre in again, and tighten and loosen the spindle clamp, and see if doing so moves the spindle in the socket.

To examine the slide rest, move the screw handles back and forth to find how much they may be moved without giving motion to the slides; this will determine the amount of lost motion between the collars of the screws and between the screws themselves and the nuts in which they operate. To try the fit of the slide rest slides, in the stationary sliding ways or Vs, remove the feed screws and move the slide so that only about one-half inch is in contact with the Vs, then move the slide back and forth laterally to see if there is any play. Move the slide to the other end of the Vs, and make a similar test, adjusting the slide to take up any play at either end. Then clean the bearing surfaces and move the slide back and forth on the Vs, and the marks will show the fit, while the power required to move the slide will show the parallelism of the Vs.

If the lathe carriage have a rack feed, operate it slowly by hand, to ascertain if it can be fed slowly and regularly by hand, which is of great importance. Then put the automatic feed in gear, and operate the feed gear back and forth, to determine how much it can be moved without moving the slide rest. To test the fit of the feed screw to the feed nut, put the latter in gear and operate the rack motion back and forth.

To determine whether the cross slide is at a right angle with the ways or shears, take a fine cut over a radial face, such, for example, as the largest face plate, and test the finished plate with a straight edge. If the face plate runs true and shows true with a straight edge, so that it is unnecessary to take a cut over it, grind a piece of steel a little rounding on its end, and fasten it in the tool post or clamp, with the rounded end next to the face plate. Let the rounded end be about ¹⁄₄ in. away from the face plate, and then put the feed motion into gear, and, with the steel near the periphery of the face plate, let the carriage feed up until the rounded steel end will just grip a piece of thin paper against the face plate tight enough to cause a slight strain in pulling the paper out, then wind the tool in towards the lathe centre and try the friction of the paper there; if equal, the cross slide is true.

To find the amount of lost motion in the screw feed gear, adjust it ready to feed the saddle, and pull the lathe belt so as to revolve the cone spindle backward, until the slide rest saddle begins to move, then mark a fine line on the lathe bed making the line coincident with the end of the lathe saddle or carriage. Then revolve the cone spindle forward, and note how much the cone spindle rotates before the saddle begins to traverse.

If the lathe has an independent feed motion it may be tested in the same manner as above.

In large lathes this is of great consideration, because the work revolves very slowly, and if there is much lost motion in the feed gear, it may take considerable time after the feed is put in gear before the carriage begins to travel. Suppose, for example, a 14-foot pulley is being turned, and that the tool cuts at 15 feet per minute, it will take nearly three minutes for the work to make a revolution.

Chapter VIII.—SPECIAL FORMS OF THE LATHE.

The lathe is made in many special or limited forms, to suit particular purposes, the object being to increase its efficiency for those purposes, which necessarily diminishes its capacity for general work.

In addition to this, however, there are machine tools whose construction varies considerably from the ordinary form of lathe, which nevertheless belong to the same family, and must, therefore, be classified with it, because they operate upon what is essentially lathe work. Thus boring and turning mills are essentially what may be termed horizontal lathes.

Figs. 650 to 655 inclusive, represent the American Watch Tool Company’s special lathes for watch-makers, which occupy a prominent position in Europe, as well as in the United States.

In lathes of this class, refinement of fit, alignment, truth, and durability of parts are of the first importance, because of the smallness of the work they perform, and the accuracy to which that work must be made. Furthermore, such lathes must be constructed to hold and release the work as rapidly as possible, because in such small work the time occupied by the tools in cutting is less, while that occupied in the insertion and removal of it is greater in comparison than in larger jobs; it often takes longer to insert and remove the work than to perform it.

These facts apply with equal force to all such parts as require the removal to or from the lathe-bed, or frequent adjustment upon the same. Thus the devices for holding and releasing the tool post or hand rest and tailblock are each so constructed that they may be set without the use of detached wrenches.

Fig. 650 represents a general view of the lathe, while Fig. 651 represents a sectional view of the headstock. The live spindle consists of two parts, an outer sleeve a a, having journal bearing in the head, and an inner hollow spindle b b, threaded at its front end e, to receive the chucks. The main spindle at the front end works in a journal box c, that is cylindrical to fit the headstock, but double coned within to afford journal bearing to the spindle a. The inner step of this double cone is relied upon mainly to adjust the diametral fit of the bearing, while the outer step is relied upon mainly to adjust the end fit of the spindle; but it is obvious in both cases there is an action securing simultaneously the diametral and the end fit. In the back bearing there are two cones. The outer one r is cylindrical outside where it fits into the head, and coned in its bore to receive the second cone s, which rotates with spindle a. The nut f is threaded upon a, so that by operating f, a is drawn within c, and s is simultaneously moved within r, so that both bearings are simultaneously adjusted. d d are dust rings, being ring-caps which cover the ends of the bearings and the oil holes so as to prevent the ingress of dust.

The inner spindle b has a bearing in a at the back end to steady it, and a bearing at end e, and is provided with the hand wheel h, by which it may be rotated to attach the chucks which screw into its mouth at e. To rotate or drive the chucks there is in a a feather at g, the chucks having a groove to receive this feather and screwing into b at e, when b is rotated.

The mouth of a is coned, as shown at h, and the chucks are provided with a corresponding male cone, as shown at h in Figs. 652 and 653, so that the chucks are supported and guided by the cone, and are therefore as close to the work as possible while having a bearing at g. But the cone on the chucks being split, (as is shown in Fig. 652), rotating b while holding a stationary (which may be done by means of the band pulley p), causes the chucks to move endwise in a, and if the motion is in the direction to draw the chuck within a, the cone h causes the chuck to close upon and grip the work. Thus in Fig. 652 is shown a step chuck. The thread at j enters the end e of b, in Fig. 651, which screws upon it. Cone h fits mouth h in Fig. 651, and l represents the splits in the chuck, which enable it to close when the cone h is drawn within the mouth h of spindle a.

The chuck is employed to hold cylindrical plates or discs, such as wheels and barrels, and the various steps are to suit the varying diameters of these parts in different sizes of watches.

Fig. 653 represents a wire chuck, having the cone at h, and the three splits at l, as before, the cone-mouth h closing the chuck as the latter is drawn within the spindle a.

In both the chucks thus far described, the construction has been arranged to close the splits and thus grip the circumferences of cylindrical bodies, but in Fig. 654 is shown the arrangement for enabling the chuck to expand and grip the bores of hollow work, such as rings, &c.

The outer spindle a corresponds to the outer spindle a in Fig. 651, and the inner one to spindle b in that figure. The chuck is here made in two separate parts, a sleeve v fitting in and driven by a, and a plug x fitting into a cone in the mouth of v, and screwing into the end of drawing spindle b. But while v is driven by and prevented from rotating within a by means of the feather at g, so likewise x is prevented from rotating within v by means of a feather h fast in x and fitting into a groove or featherway in v. It follows then that when b is rotated x may be traversed endways in v, to open or close the steps y according to the direction of rotation of b.

It will now be apparent that in the case of chucks requiring to grip external diameters, the gripping jaws of the chucks will, when out of the lathe, be at their largest diameter, the splits l being open to their fullest, and that when by the action of the cones, they are closed to grip the work, such closure must be effected against a slight spring or resistance of the jaws, and this it is that enables and causes the chuck to open out of itself, when the enveloping cone permits it to do so.

But in the case of the opening or expanding chuck, the reverse is the case, and the chuck is at its smallest diameter (the splits l being at their closest) when the chuck is removed from the lathe, as is obviously necessary. In reality the action is the same in both cases, for the chuck moves to grip the work under a slight resistance, and this it is that enables it to readily release the work when moved in the necessary endwise direction.

The band pulley p is fast upon a, and is provided with an index of 60 holes on its face g, and which are adjusted for any especial work by a pin q, so that a piece of work may have marked on it either 60, 30, 20, 15, 12, 10, 6, 5, 4, 3, or 2 equidistant lines of division, each of those numbers being divisors of 60. In marking such lines of division upon the work a sharp point may be used, supported by the face of the hand rest as a guide; or a sharp-pointed tool may be placed in the slide rest to cut a deeper line upon the work. The index plates used for cutting wheels and pinions may be placed on the rear end of a, the pawl being secured to the work-bench. The wheel h is for rotating spindle b to screw the chucks on or off the same.

Fig. 655 represents an end view from the tailstock end of the lathe; a′ is the bed having the angles a a to align the heads and rests. The means of holding or releasing the tailstock, on the lathe-bed, is the same as that for holding the headstock, the construction being as follows: b is the shoulder of a bolt through which passes the shaft c, with a lever d to operate it. This shaft is eccentric where it passes through the bolt, so that by using the lever aforesaid the bolt secures or releases the head according to the direction in which it is moved. A very small amount of motion is needed for this. The standard for the hand rest is split, and a screw is used to tighten it in an obvious manner, the screw being operated by the handle e′. An end view of the rest, showing the device for securing the foot h to the bed, is shown in Fig. 656, f is a shoe spanning the bed and fitting to the bed angles a. Through f passes the bolt g, its head passing into the T-shaped groove h; n′ is a hand wheel for operating bolt g. At s is a spiral spring, which by exerting an end pressure on washer w and nut n′, pulls g and the head h down upon f, and therefore f down upon the bed, whether the rest be locked to the bed or not; hence when n′ is released to remove or adjust the rest, neither dust nor fine cuttings can pass either between the rest and shoe or the shoe and the lathe-bed, and the abrasion that would otherwise occur is thus avoided.

Two qualities of these lathes are made: in the better quality all the working parts are hardened and afterwards ground true. In the other the parts are also ground true, but the parts (which in either case are of steel) are left soft for the sake of reducing the cost. In all, the parts are made to gauge and template, so that a new head, tailstock, or any other part in whole or in detail may be obtained from the factory, either to make additions to the lathe or to replace worn parts.

Two styles of slide rest are made with these lathes: in the first, shown in Fig. 657, the swivel for setting the top slide at an angle for taper turning is at the base of the top slide, hence the lower slide turns all radial faces at a right angle to the line of lathe centres. In the second, Fig. 658, there is a third slide added at the top, so that the bottom slide turns radial faces to a right angle with the line of lathe centres, the next slide turns the taper and the top slide may be used to turn a radial face at a right angle to the surface of the taper, and not at a right angle to the axis of the work. Both these rests are provided with tool post clamps, to hold tools made of round wire, such clamps being shown in position in figure 657.

Fig. 659 represents an additional tailstock for this lathe, the tail spindle lying in open bearings so that it can be laid in, which enables the rapid employment of several spindles holding tools for performing different duties, as drilling, counter-boring, chamfering, &c.

Fig. 660 represents a filing fixture to be attached to the bed in the same manner as the slide rest. It consists of a base supporting a link, carrying two hardened steel rolls, upon which the file may rest, the rolls rotating by friction during the file strokes, and serving to keep the file flat and fair upon the work.

Fig. 661 represents a fixture for wheel and pinion cutting; it is attached to the slide rest. When the cutter spindle is vertical the belt runs directly to it from the overhead counter shaft, but when it is horizontal the belt passes over idler pulleys, held above the lathe. The cutter spindle is carried on a frame, pivoted to the sliding piece on the vertical slide, so that it may be swivelled to set in either the vertical or horizontal position.

Fig. 662 represents a jewelers’ rest for this lathe. It fits on the bed in the place of the tailstock, and is used for cutting out the seats for jewels, in plates, or settings. It is especially constructed so as to receive the jewel at the top and bore the seating to the proper diameter, without requiring any measurements or fitting by trial, and the manner in which this is accomplished is as follows:—