Modern Machine-Shop Practice Part 50

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 cla.s.sified 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 cla.s.s, 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 s.c.r.e.w.i.n.g 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 circ.u.mferences 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 s.c.r.e.w.i.n.g 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.

[Ill.u.s.tration: _VOL. I._ =WATCHMAKER'S LATHE.= _PLATE VIII._

Fig. 650.

Fig. 651.

Fig. 652.

Fig. 653.

Fig. 654.]

[Ill.u.s.tration: _VOL. I._ =DETAILS OF WATCHMAKER'S LATHE.= _PLATE IX._

Fig. 655.

Fig. 656.

Fig. 657.

Fig. 658.

Fig. 659.

Fig. 660.

Fig. 661.

Fig. 662.]

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 pa.s.ses the shaft _c_, with a lever _d_ to operate it. This shaft is eccentric where it pa.s.ses 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_ pa.s.ses the bolt _g_, its head pa.s.sing 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 pa.s.s 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 pa.s.ses 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:--

[Ill.u.s.tration: Fig. 663.]

[Ill.u.s.tration: Fig. 664.]

[Ill.u.s.tration: Fig. 665.]

Fig. 663 is a side elevation, Fig. 664 an end elevation, and Fig. 665 a plan view of this rest, and similar letters of reference indicate like parts in each of the three figures. A is the base, held to the lathe bed by the bolt B, whose operation is the same as that already described for the head and tailstocks.

In one piece with A is the arm C, carrying at its head three gauge tongues or pieces D E F, which are adjustable by means of the screws _d_ _e_ _f_, which move the gauge tongues horizontally. Through a suitable guide I is a standard or head; pivoted to A at J J, and carrying at its top three gauge tongues K L M.

Midway between pivots J J and the ends of the gauge tongues, is the centre or tool carrying spindle O. If a piece of work, as a jewel, be placed between the tongues F and M, Fig. 664 [swinging M, and with it I (which is pivoted at J), laterally], then the point of the centre N will be thrown out of line with the lathe live spindle half the diameter of the jewel, because from J to the centre N, of O, is exactly one half of the vertical distance from J to the jewel. If then a tool be placed in the dead centre and its cutting edge is in line with the axis of spindle O, it will bore a hole that will just fit the jewel. Hence placing the jewel between the two tongues sets the diameter to which the tool will bore and determines that it shall equal the diameter of the jewel.

The object of having three pair of gauge tongues is to enable the obtaining of three degrees of fit; thus with a piece placed between D K the hole may be bored to fit the piece easily, with it placed between E L the fit may be made barely movable, while with it placed between F M the fit may be too tight to be a movable one save by pressure or driving, each degree of fit being adjusted by means of the screws _e_ _f_ _g_.

The tool is fed by moving spindle O by hand, the screw P being adjusted so that its end abuts against stop Q, when the hole is bored to the requisite depth; R is simply a guide for the piece S, which being attached to O, prevents it from rotating.

In watch manufactories special chucks and appliances are necessary to meet their particular requirements. There is found to exist, for example, in different rods of wire of the same nominal diameter, a slight variation in the actual diameter, and it is obvious that with the smaller diameters of wire the split chucks will pa.s.s farther within the mouth _h_ of A, Fig. 651, because the splits of the chucks will close to a greater extent, and the cones on the chucks therefore become reduced in diameter.

If then it be required to turn a number of pieces of work to an exact end measurement, or a number of f.l.a.n.g.es or wheels to equal thicknesses, without adjusting the depth of cut for each it becomes necessary to insure that the successive pieces of work shall enter the chucks to an equal distance, notwithstanding any slight variation in the work diameter at the place or part where it is gripped by the chuck.

To accomplish this end what is termed a sliding-spindle head is employed. In this the _outer spindle_ has the end motion necessary to open and close the chuck, the chuck having no end motion.

[Ill.u.s.tration: Fig. 666.]