Modern Machine-Shop Practice Part 44

With the lever L in the position shown, neither B nor E engages with A, hence they are at rest; but if lever L be raised as in Fig. 567, B will gear with wheels A and C, and motion will be conveyed from A to C, wheel E running as an idle wheel, thus C will revolve in the same direction as the lathe spindle.

But if lever L be lowered as in fig. 568, then wheel E will gear with and receive motion from A, which it will convey to B, and C will revolve in the opposite direction to that in which the lathe spindle runs. To secure lever L in position, a pin F pa.s.ses through it and into holes as I, J, provided in the lathe head. Lever L is sometimes placed inside the head, and sometimes outside as in Fig. 569, and it will be obvious that it may be used to cut left-hand threads without the use of an extra intermediate change gear, which is necessary in the construction shown in Fig. 570, in order to reverse the direction of lead screw revolution.

Sometimes the pin F is operated by a small spring lever attached to L, so that the hand grasps the end of L and the spring lever simultaneously, removing F from the hole in H, and therefore freeing L, so as to permit its operation. By relaxing the pressure on the small spring lever pin F finds its own way into the necessary hole in H, when opposite to it, without requiring any hand manipulation.

In larger lathes the lever L is generally attached to its stud outside the end bearing of the head H.

[Ill.u.s.tration: Fig. 568.]

It is preferable, however, that the device for changing the direction of feed traverse be operative from the lathe carriage as in the Sellers lathe, so that the operator need not leave it when it is necessary to reverse the direction of traverse.

[Ill.u.s.tration: Fig. 569.]

The swing frame, when the driving gear D is outside of the back bearing (as it is in Fig. 570), is swung from the axis of the lead screw as a centre of motion, and has two slots for receiving studs for change wheels. But when the driving gear is inside the back bearing as in Fig.

571, the swing frame may be suspended from the spindle (R, Fig. 565) that pa.s.ses through the lathe head, which may also carry the cone for the independent feed as shown in Fig. 571, no matter on which side of the lathe the lead screw and feed rod are. This affords the convenience that when both lead screw and feed rod are in front of the lathe, the feed may be changed from the screw cutting to the rod feed, or _vice versa_, by suitable mechanism in the ap.r.o.n, without requiring any change to be made in the driving gears.

[Ill.u.s.tration: Fig. 570.]

In the lathe shown in Fig. 572, which is from the design of S. W.

Putnam, of the Putnam Tool Company of Fitchburg, Ma.s.sachusetts, the cone pinion for the back gear, and that for driving the feed motion, are of the same diameter and pitch, so that the gear-wheel L in Fig. 573 may (by means of a lever shown dotted in) be caused to engage with either of them. When the latter is used in single gear it would obviously make no difference which wheel drives L, but when the back gear is put in and L is engaged with the cone pinion, its speed corresponds to that of the cone, which being nine times faster than the live spindle, enables the cutting of threads nine times as coa.r.s.e as if the back gear was not in use. This affords very great advantages for cutting worms and threads of coa.r.s.e pitches.

An excellent method of changing the direction of feed motion, and of starting or stopping the same, is shown in Fig. 574, which represents the design of the Ames Manufacturing Company's lathe.

[Ill.u.s.tration: Fig. 571.]

In the figure, A is the small step of the lathe cone, B the pinion to drive the back gear, C a pinion to drive the feed gear, giving motion to D, which drives E, the latter being fast to G and rotating freely upon the shaft F, G drives H, which in turn drives I. The clutch J has a featherway into which fits the feather _c_, on the shaft F, so that when the clutch rotates it rotates J through the medium of _c_; K is a circular fork in a groove in J, and operated by a lever operated by a rod running along the front of the lathe bed. This rod is splined so that a lever carried by the ap.r.o.n or feed-table, having a hub and enveloping the rod, may by means of a feather filling into the spline operate the rod by partly rotating it, and hence operate K. Suppose now that this lever stands horizontal, then the clutch J would stand in the position shown in the cut, and D, E, G, H, and I, would rotate, while F would remain stationary. By lifting the lever, however, J would be moved laterally on F (by means of K) and the lug _a_ on J would engage with lug _b_ on G, and G would drive J, which through _c_ would drive F, on which is placed a change gear at L, thus traversing the carriage forward. To traverse it backward the lever would be lowered or depressed below the horizontal level moving K, and therefore J, to the right, so that lug _a_ would engage with lug _b_ on I, hence F would be driven by I, whose motion is in an opposite direction to G, as is denoted by the respective arrows.

[Ill.u.s.tration: Fig. 572.]

To throw all the feed motion out of gear, to run the lathe at its quickest for polishing, &c., the operation is as follows.

[Ill.u.s.tration: Fig. 573.]

M is tubular and fast in N and affords journal bearing to wheel D.

Through M pa.s.ses stud O, having a k.n.o.b handle at P. At the end of the hub of D is a cap fast in D, the latter being held endways between the shoulder shown on O and the washer and nut T. If then P be pulled outwards O will slide through M, and through the medium of T will cause D to slide over M, in the direction of the arrow, and pa.s.s out of gear from C, motion therefore ceasing at C.

Q is the swing frame for the studs to carry the change wheels, and R a bolt for securing Q in its adjusted position. S is a journal and bearing for H.

If it be considered sufficient the feed motion on small lathes (instead of feeding in both directions on the lateral and cross feeds as in the Putnam Lathe), may feed in the direction from the dead to the live centre, and in one direction only on the cross slide.

[Ill.u.s.tration: Fig. 574.]

An example of a feed motion of this kind is shown in Figs. 575 and 576; _f_ _f_ is the feed spindle splined and through the medium of a feather driving the bevel pinion A having journal bearing in B. Pinion A drives the bevel gear C, which is in one piece with pinion D. The latter drives gear F, which drives pinion K, which is carried on a lever L, pivoted on the stud which carries F, so that by operating L, pinion K is brought into gear with pinion P, which is fast upon the cross-feed screw, and therefore rotates it to effect the automatic cross feed.

[Ill.u.s.tration: Fig. 575.]

[Ill.u.s.tration: Fig. 576.]

As shown in the cut, the lever L is in such a position as to throw K out of gear with P, and the cross feed screw is free to be operated by the handle by hand. At M is a slot in L in which operates a cam or eccentric, one end of which projects into L, while at the other end is the round handle R, Fig. 575, which is rotated to raise or lower that end of L so as to operate K. To operate the saddle or carriage the motion is continued as follows:--at the centre of F is a pinion gear G which operates a gear H, which is in one piece with the pinion I, and the latter is in gear with the rack running along the lathe bed.

If the motion from A to I was continuous, the carriage feed or traverse would be continuous, but means are provided whereby motion from F to I may be discontinued, as follows:--A hand traverse or feed is provided.

J, Figs. 575 and 576, is carried by a stud having journal bearing in a hub on X and receiving the handle Q; hence by operating Q, J is rotated, operating the gear H, upon which is the pinion I, which is in gear with the rack running along the lathe bed.

To lock the carriage in a fixed position, as is necessary when operating the cross feed on large radial surfaces, the following device is provided:--N is a stud fixed in a hub on X, and having a head which overlaps the rim of H, as shown in figure. On the other side of that rim is a washer Z on the same stud having a radial face also overlapping the rim of H, but its back face is bevelled to a corresponding bevel on the radial face on the hub of lever O (the hub of O being pivoted on the same stud). When therefore O is depressed the two-bevel face of the hub of O forces the washer Z against the face of the wheel H, whose radial faces at the rim are therefore gripped between the face of the collar N and that of the washer Z, hence H is locked fast. By raising the end of lever O, Z is released and H is free to rotate.

Both the carriage feed and cross feed can only be traversed in one direction so far as these gears and levers are concerned, but means are provided on the lathe headstock for reversing the direction of motion of the feed spindle _f_ so as to reverse the direction of the feeds. It will be observed that so long as _f_ rotates, A, C, D, and F rotate, the remaining motions only operating when S is screwed up.

In order to obtain a delicate tool motion from the handle Q it is necessary to reduce the motion between J and I as much as possible, a point in which a great many lathes as at present constructed are deficient, because Q, although used to simply traverse the carriage along the bed, in which case rapid motion of the latter is desirable, is also used to feed the tool into corners when the lathe has no compound rest to put on light cuts on radial faces, hence it should be capable of giving a delicate tool motion.

[Ill.u.s.tration: Fig. 577.]

On account of the deficiency referred to it is often necessary to put on a fine radial cut by putting the feed traverse in gear, and, throwing the feed screw gear out of contact with the other change wheels, pull it around by hand to put on the cut. In compound slide rests these remarks do not apply, because the upper part of the rest may be used instead of the handle Q.

Many small lathes are provided with a tool rest known as the _elevating rest_, or weighted lathe.

An excellent example of an elevating rest for a weighted lathe is shown in Figs. 577 and 578, which represent the construction in the Pratt and Whitney lathe. A is the lathe shears upon which slides the carriage provided with [V] slideways R for the sliding piece B, and provided at the other end with the guides H. The cross slide S is pivoted upon B at D, and fits at the other end between the guides H. At E is the elevating screw which when operated raises or lowers that end of the elevating rest to adjust the tool height. This also affords an excellent means of making a minute adjustment for depth of tool cut. The tool rest F is bolted to S.

[Ill.u.s.tration: Fig. 578.]

The weight W is suspended from S and, therefore, holds one end of S to B, the lathe to C, and C to A; at the other end the weight holds S to C (through the medium of the elevating screw E) and C to A. The cross feed nut N is fast to S, the cross feed screw being operated by hand wheel G.

B is provided with the [V] slideways R, which slide upon corresponding [V] slides R' upon C; P is a lug cast upon C, and K is a screw threaded in B. When the end of screw K abuts against P the motion of S, and, therefore, of the cutting tool T, towards the work is arrested, hence when the tool is adjusted to the proper depth of cut, K is operated to abut firmly against P, and successive pieces may be turned to the same diameter without requiring each piece to be measured for diameter. N is the handle for opening and closing the nut for the feed screw Q, and Z is the wheel for the hand feed traverse. The length of cross feed motion is determined by the length of the cross [V] slides R'.

This cla.s.s of rest possesses the advantage that no lost motion in the slides occurs by reason of the wear, because the weight keeps the parts in constant contact notwithstanding such wear; on the other hand, however, the slide [V]s sustain the extra wear due to the weight W in addition to the weight of the carriage. Lathes of this cla.s.s are intended for light work, and are less suited for boring than for plain turning; they are, however, very convenient, and are preferred by many to any other kind of lathe for short and light work.

[Ill.u.s.tration: Fig. 579.]

The tool rest being removable may be supplanted by other special forms of rest. Thus Figs. 579 and 580 represent a special rest for carrying two tools to cut pieces of work to the exact same length. Bolts D and E are to secure the rest A to the elevating rest, and C C are the clamps for the two tools B.

[Ill.u.s.tration: Fig. 580.]

Fig. 581 represents a cross sectional view of the Putnam Tool Company's gibbed elevating rest, there being a gib on the underneath side of the front shear. The elevating screw is pivoted by a ball joint. By employing a gib instead of a weight, the bed may be provided with cross girts or ribs joining the two sides of the shear, thus giving much greater stiffness to it.

Figs. 582, 583, and 584 represent a lathe feed motion by William Munzer, of New York. The object in this motion is to insure that no two feeds can be put into operation simultaneously, because putting the feed in motion in one direction throws it out of gear for either of the others.

Another object is to have the transmitting motion as direct as possible so as to avoid the rotation of any wheels not actually necessary for the transmission of the motion; and a third object is to enable the throwing out of gear of all wheels (when no feed motion at all is required) without leaving the ap.r.o.n.

The means employed to effect these objects are as follows:--

In Fig. 582 _f_ represents the independent feed spindle and S the lead-screw: _f_ is splined to drive A, A' and A", which is a sleeve in one piece, and consists of a circular rack at A, a bevel pinion at A', and a second bevel pinion at A". This sleeve may be operated in either direction along _f_ by rotating the pinion B. As shown in the cut A' and A" are both out of gear with the bevel-wheel C, but if B be rotated to the right then A' will be in gear with C, or if it be operated to the left then A" will be in gear with C. Now the direction of rotation of C will be governed by which pinion, A' or A", drives it, and these are the means by which the direction of the feed traverse and also of the cross feed is determined.

If none of the feeds are required to operate, the sleeve occupies the position shown in the cut, and the circular rack at A simply rotates while B and all other parts remain at rest. On the same central pin as C is the pinion D driving a spur gear E". On the same centre pin as E is the gear F driving G, which is on the same central pin as C and D. The gear H is fixed to and rotates with G and drives I; all these gears serving to reduce the speed of motion when operating to feed the carriage traverse in either direction.

A gear J is carried on the end of a lever K, being pivoted at L. In the position shown J is out of gear with all gears, but it may be swung to the right so as to engage with wheel I and wheel M, and convey the motion of I to M. Upon the same spindle as M is the pinion N, engaging with the rack O, which is fast on the lathe bed. This completes the automatic feed traverse.

For a hand feed traverse, pinion P is employed to drive M, which is fast to N. The cross feed is self-acted by moving lever K to the left, causing it to engage with pinion Q as well as with T, Q being fast on the cross feed screw. To lock J in either of its three positions there is provided on lever K a spring locking pin R, shown clearly in Fig.

584, which represents an irregular section of the gearing viewed from the headstock of the lathe. The pin R is pressed inward by the spiral spring shown, and has a conical end fitting into holes provided in the ap.r.o.n to receive it. There are three of these holes, shown in dotted lines at _a_ _b_ _c_ in Fig. 582. When the pin is in _a_ the lever K, and therefore wheel J, Fig. 582, is locked out of gear; when it is in hole _b_ wheel J is locked in gear with I and M, and when it is in _c_ the wheel J is in gear with T and Q, and the cross feed is actuated.

[Ill.u.s.tration: Fig. 581.]

[Ill.u.s.tration: Fig. 582.]