Modern Machine-Shop Practice Part 36

[Ill.u.s.tration: Fig. 495.]

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:--

[Ill.u.s.tration: Fig. 496.]

In G is a radial slot through which pa.s.ses a bolt I provided with a cap nut H, in M is an annular groove J. When I is lifted its head pa.s.ses 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 pa.s.ses 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 pa.s.sing 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 uns.c.r.e.w.i.n.g 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_ pa.s.sing 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.

[Ill.u.s.tration: Fig. 497.]

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.

[Ill.u.s.tration: Fig. 498.]

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 s.c.r.e.w.i.n.g 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.

[Ill.u.s.tration: 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).

[Ill.u.s.tration: 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 pa.s.s 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 pa.s.sing 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 ap.r.o.n. 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 ap.r.o.n 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 ap.r.o.n as seen in Fig. 501, and is splined as shown at _h_. At I is a bracket fast upon the ap.r.o.n 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 pa.s.sing 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 ap.r.o.n 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' pa.s.sing through the slot M" in G. s.c.r.e.w.i.n.g 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 s.c.r.e.w.i.n.g 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.

[Ill.u.s.tration: Fig. 501.]

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 ap.r.o.n 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" pa.s.ses 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' pa.s.sing 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 ap.r.o.n 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 pa.s.ses; _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_ s.c.r.e.w.i.n.g through W and into the groove O'.

[Ill.u.s.tration: Fig. 502.]

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'.

[Ill.u.s.tration: Fig. 503.]

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 pa.s.s 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:--