Modern Machine-Shop Practice Part 51

The construction of this sliding-spindle head is shown in Fig. 666, in which a wire chuck is shown in position in the spindles; L is the live spindle pa.s.sing through parallel bearings, so that it may have end motion when the nut M is operated. The inner spindle N to which the chucks are screwed is prevented from having end motion by means of the collar _p_ and nut _q_ at the rear bearing. When nut M is rotated and N is held stationary by means of the pulley P, L slides endways, and the chuck opens or closes according to the direction in which the nut moves the spindle L.

To regulate the exact distance to which the work shall be placed within the chuck, a piece of wire rod may be placed within the hollow spindle N being detained in its adjusted position by the set screw S.

The construction whereby the nut is permitted to revolve with spindle L, and be operated by hand to move spindle L when the lathe is at rest, is as follows.

The cylindrical rim _t_ of the nut is provided with a series of notches arranged around its circ.u.mference. R is a lever whose hub envelops nut M, but has journal bearing on V. R receives the pin S, which rests upon a spiral spring T. When, therefore, S is pushed down it depresses the spring T and its end W enters some one of the notches in the rim _t_, and operates the nut after the manner of a ratchet. But so soon as the end pressure on R is released, the spiral spring lifts it and M is free to revolve with L as before. The inner spindle is driven by means of the feather G.

Pulley P has two steps Y for the belt, and a friction step _z_, around which pa.s.ses a friction band operated by the operator's foot to stop the lathe quickly. This performs two functions, as follows. The thread of M is a left-hand one so that the inertia of the nut will not, when the lathe is started, operate to screw the nut back, and release the chuck jaws from the work, by moving spindle L endwise. Per contra, however, in stopping the lathe suddenly by means of the brake, there is a tendency of nut M to stop less quickly than spindle L, and this operates to unscrew nut N and release the work. To a.s.sist this R is sometimes in lathes for watch manufactories provided with a hand wheel whose weight is made sufficient for the purpose.

[Ill.u.s.tration: Fig. 667.]

[Ill.u.s.tration: Fig. 668.]

Figs. 667 and 668 represent a pump centre head for watch manufactories, being a device for so chucking a piece of work that a hole may be chucked true and enlarged or otherwise operated upon, with the a.s.surance that the work will be chucked true with the hole. Suppose two discs be secured together at their edges, their centres being a certain distance apart, as, for example, a top and bottom plate of a watch movement, and that the holes of one plate require to be transferred to the other, then by means of this head they may be transferred with the a.s.surance that they shall be axially in line one with the other, and at a right angle to the faces of the plates, as is necessary in setting jewels in a watch movement.

In holes of such small diameters as are used in watch work, it is manifestly very difficult to set them true by the ordinary methods of chucking and it is tedious to test if they are true, and it is to obviate these difficulties that the pump centre head is designed. Its operation is as follows.

There are in this case three spindles A, B, and C, in Fig. 667; A corresponds to spindle A in Fig. 651, driving the chuck D which screws on A as shown; B simply holds the work against the face _d_ of D, and C holds the work true by means of the centre _e_, which enters the hole or centre in the work and is withdrawn when the work is secured by spindle B.

The chuck D is open on two sides as shown at E E in Fig. 668, which is an end face view of the chuck, and through these openings the work is admitted to the chuck. The rod or spindle C is then pushed, by hand, endwise, its centre _e_ entering the hole or centre in the work (so as to hold the same axially true) and forcing the work against the inside faces _d_, spindle B is then operated, the face _p_ forcing the work against face _d_, and between these two faces _d_ _p_ the work is held and driven by friction. The spindle C and its centre _e_ is then withdrawn by hand, leaving the hole in the work free to be operated upon.

The journal bearings for spindle A are constructed as described for A in Fig. 666; spindle B is operated endways within A as follows. A is threaded at G to receive the hub H of wheel I, at the end of B is a collar which is held to and prevented from end motion within the hub H: hence when wheel I is rotated and A is held stationary (by means of the band pulley), H traverses on G and carries B with it. Operating I in one direction, therefore moves _p_ against the work, while operating it in the other direction releases face _p_ from contact with the work.

It is obviously of the first importance that the spindle C be held and maintained axially true, notwithstanding any wear, and that it be a close fit within B so as to remain in any position when the lathe is running, and thus obviate requiring to remove it. To maintain this closeness of fit the following construction is designed. Between spindle A and spindle B, at the chuck end of the two, is a steel bush which can be replaced by a new one when any appreciable wear has taken place.

Between B and C are two inverted conical steel bushes, which can also be replaced by new ones, to take up any wear that may have taken place.

[Ill.u.s.tration: Fig. 669.]

Fig. 669 represents an improved hand lathe by the Brown and Sharpe Manufacturing Company, of Providence, R. I. It is specially designed for the rapid production of such cylindrical work as may be held in a chuck, or cut from a rod of metal pa.s.sing through the live spindle, which is hollow, so that the rod may pa.s.s through it. Short pieces may be driven by the chuck or between the centres of a face plate (shown on the floor at _e_) s.c.r.e.w.i.n.g on in the ordinary manner. When, however, this face plate is removed a nut _d_ screws on in its stead, to protect the thread on the live spindle.

The chuck for driving work in the absence of face plate _e_ (as when the rod from which the work is to be made is pa.s.sed through the live spindle) may be actuated to grip or release the work without stopping the lathe. The pieces _j_ _j_ are to support the hand tool shown in Figs. 1313 and 1314, in connection with hand turning, the tool stock or handle being shown at _k_ on the floor. The lever for securing the tailstock to or releasing it from the shears is shown at _t_. The tail spindle is operated by a lever pivoted at _g_ so that it may be operated quickly and easily, while the force with which the tail spindle is fed may be more sensitively felt than would be the case with the ordinary wheel and screw, this being a great advantage in small work. The tail spindle is also provided with a collar _r_, that may be set at any desired location on the spindle to act as a stop, determining how far the tail spindle can be fed forward, thus enabling it to drill holes, &c., of a uniform depth, in successive pieces of work.

The live spindle is of steel and will receive rods up to 1/2 inch in diameter. Its journals are hardened and ground cylindrically true after the hardening. It runs in bearings which are split and are coned externally, fitting into correspondingly coned holes in the headstock.

These bearings are provided with a nut by means of which they may be drawn through the headstock to take up such wear in the journal and bearing fit, as may from time to time occur.

[Ill.u.s.tration: Fig. 670.]

It is obvious that the lathe may be removed from the lower legs and frame and bolted to a bench, forming in that case a bench lathe.

Fig. 670 represents a special lathe or screw slotting machine, as it is termed, for cutting the slots in the heads of machine or other screws.

The live spindle drives a cutter or saw _e_, beneath which is the device for holding the screws to be slotted, this device also being shown detached and upon the floor.

The screw-holding end of the lever _a_ acts similarly to a pair of pliers, one jaw of which is provided on handle _a_, while the other is upon the piece to which _a_ is pivoted. The screw to be slotted is placed between the jaws of _a_ beneath _e_; handle _a_ is then moved to the left, gripping the screw stem; by depressing _a_, the screw head is brought up to the cutter _e_ and the slot is cut to a depth depending upon the amount to which _a_ is depressed, which is regulated by a screw at _b_; hence after _b_ is properly adjusted, all screw heads will be slotted to the same depth.

The frame carrying the piece to which _a_ is pivoted may be raised or lowered to suit screws having different thicknesses of head by means of a screw, whose hand nut is shown at _d_.

The frame for the head of the machine is hollow, and is divided into compartments as shown, in which are placed the bus.h.i.+ngs used in connection with the screw-gripping device, to capacitate it for different diameters of screws, and also for the wrenches, cutters, &c.

[Ill.u.s.tration: Fig. 671.]

[Ill.u.s.tration: Fig. 672.]

[Ill.u.s.tration: Fig. 673.]

Figs. 671, 672, and 673, represent a lathe having a special feed motion designed and patented by Mr. Horace Lord, of Hartford, Connecticut. Its object is to give to a cutting tool a uniform rate of cutting speed (when used upon either flat or spherical surfaces), by causing the rotations of the work to be r.e.t.a.r.ded as the cutting tool traverses from the centre to the perimeter of the work, or to increase as the tool traverses from a larger to a smaller diameter. If work of small diameter be turned at too slow a rate of cutting speed, it is difficult to obtain a true and smooth surface; hence, as the tool approaches the centre, it is necessary to increase the speed of rotation. As lathes are at present constructed, it is necessary to pa.s.s the belt from one step to another of the driving cone, to increase the speed. In this two disadvantages are met with. First, that the increase of speed occurs suddenly and does not meet the requirements with uniformity. Second, that the strain upon the cutting tool varies with the alteration of cutting speed. As a result, the spring of the parts of the lathe, as well as of the cutting tool, varies, so that the cut shows plainly where the sudden increase or decrease (as the case may be) of cutting speed has occurred. The greatest attainable degree of trueness is secured when the cutting speed and the strain due to the cut are maintained constant, notwithstanding variations of the diameter.

This, Mr. Lord accomplishes by the following mechanism: Instead of driving the lathe from an ordinary countershaft, he introduces a pair of cones which will vary the speed of the lathe as shown in Fig. 672 as applied to ball turning. L is a belt cone upon the counter-shaft driven from the line shaft. L drives H, which may be termed the lathe countershaft, and from the stepped cone K the belt is connected to the lathe in the usual manner. P is a s.h.i.+pper bar to move the belt N upon and along the belt cones, and thus vary the speed. R is a vertical shaft extending up at the end of the lathe and carrying a segment. This segment is connected to the belt s.h.i.+pper bar P by two cords, one pa.s.sing from _r_^{1} around half the segment to _r_^{2}, and the other pa.s.sing from _r_^{3} to _r_^{4}, so that if the segment be rotated, say to the right, it and the bar will move as denoted by the dotted lines, or if moved in an opposite direction, the bar motion will correspond and move the belt N along the cones respectively left or right.

At the back of the lathe is a horizontal shaft S, similar to an ordinary feed spindle, and connected to the segment shaft by a pair of bevel gears S^{2}. Between the two ears _e_ _e_, at the rear of the lathe carriage, is a pinion _t_, which drives the splined shaft S, which works in a rack T'. The tool rest is pivoted directly beneath the ball, to be turned after the usual manner of spherical slide rests, and carries a gear _a_^{2}, which, as the rest turns, rotates a gear _a_^{3}. Upon the face of the latter is a pin _a_^{4} working in a slot _a_^{5} at the end of the rack T'; hence as the tool rest feeds, motion is transmitted from _a_^{2} through _a_^{3}, _a_^{4}, _a_, T', T, and _s_ _s_^{2} to R, which operates the belt s.h.i.+pper P. As it is the rate of tool feed that governs the speed of these motions, the effect is not influenced by irregularity in feeding; hence the speed of the work will be equalized with the tool feed under all conditions. The direction of motion of all the parts will correspond to that of the tool feed from which their motion is directed, and therefore the work speed will augment or diminish automatically to meet the requirements.

[Ill.u.s.tration: Fig. 674.]

Fig. 673 ill.u.s.trates the action of the mechanism when used for surfaces, like a lathe face plate. In this case the two gears and the rack T'

simply traverse with the cross-feed slider, and the mechanism is actuated as before. In Fig. 674 a different method of actuating the belt s.h.i.+pper is ill.u.s.trated. A pulley is attached to the intermediate stud of the change gears, being connected by belt to the s.h.i.+pper, which is threaded as shown at _d_, the belt guiding forks, as _p_^{2}, being carried on a nut actuated by the screw _d_.

CUTTING-OFF MACHINE.--The cutting-off machine is employed to cut up into the requisite lengths pieces of iron from the bar. As the cutting is done by a tool, the end of the work is left true and square and a great saving of time is effected over the process of heating and cutting off the pieces in the blacksmith's forge, in which case the pieces must be cut off too long and the ends left rough.

[Ill.u.s.tration: Fig. 675.]

Fig. 675 represents Hyde's cutting-off machine, which consists of a hollow live spindle through which the bar of iron is pa.s.sed and gripped by the chucks C C. At G is a gauge rod whose distance from the tool rest R determines the length of the work. F is a feed cone driven by a corresponding cone on the live spindle and driving the worm W, which actuates the self-acting tool feed, which is provided with an automatic motion, which throws the feed out of action when the work is cut off from the bar. The stand S is movable and is employed to support the ends of long or heavy bars.

To finish work smooth and more true than can be done with steel cutting tools in a lathe, what are known as grinding lathes are employed. These lathes are not intended to remove a ma.s.s of metal, but simply to reduce the surfaces to cylindrical truth, to true outline and to standard diameter, hence the work is usually first turned up in the common lathe to the required form and very nearly to the required diameter, and then pa.s.sed to the grinding lathe to be finished. The grinding lathe affords the best means we have of producing true and smooth cylindrical parallel work, and in the case of hardened work the only means. In place of steel cutting tools an emery wheel, revolved at high speed from an independent drum or wide pulley, is employed, the direction of rotation of the emery wheel being opposite to that of the work.

[Ill.u.s.tration: Fig. 676.]

Fig. 676 represents Pratt and Whitney's weighted grinding lathe. The headstock and tailstock are attached to the bed in the usual manner, the frame carrying the emery wheel is bolted to the slide rest as shown, the rest traversing by a feed spindle motion. The carriage traverse is self-acting and has three changes of feed, by means of the feed cones shown.

To enable the lathe to grind taper work (whether internal or external) the lathe is fitted with the Slate taper attachment shown in Figs. 508 and 509.

It is obvious that in a lathe of this kind, there must be an extra overhead shaft, driving a drum of a length equal to the full traverse of the lathe carriage, or of the plate carrying the head and tailstocks, and the arrangement of this drum with its belt connection to the pulley on the emery wheel arbor, is sufficiently shown in figure. To protect the ways of the bed from the abrasion that would be caused by the emery and water falling upon them, guards are attached to the carriage extending for some distance over the raised [V]s.

[Ill.u.s.tration: Fig. 677.]

It is essential that the work revolve in a direction opposite to that of the emery wheel, for the following reasons. In Fig. 677 let A represent a reamer and B a segment of an emery wheel. Now suppose A and B to revolve in the direction that would exist if one drove the other from frictional contact of the circ.u.mferential surfaces, then the pressure of the cut would cause the reamer A to spring vertically and a wedging action between the reamer and wheel would take place, the reamer vibrating back and forth under varying degrees of this wedging; as a result the surface of A would show waves and would be neither round nor smooth.

[Ill.u.s.tration: Fig. 678.]

In the absence of a proper grinding lathe, an ordinary lathe is sometimes improvised for grinding purposes, by attaching to the slide rest a simple frame and emery wheel arbor with pulley attached as in Fig. 678, in which A is the emery wheel, C the pulley for driving the arbor, and B the frame, D being a lug for a bolt hole to hold the frame to the lathe rest.

In some cases the work may remain stationary and the emery wheel only rotate. Thus, suppose it was required to grind the necessary clearance to relieve the cutting edge C of the reamer, then A could be rotated until C stood in the required position with relation to B, and the revolving emery wheel may either be traversed along, or the work may traverse past the wheel, according to the design of the grinding lathe, but in either case A remains stationary during each cut traverse; after each successive traverse A may be rotated sufficiently to give a cut for the next traverse.

Fig. 679 represents Brown and Sharpe's universal grinding lathe.

[Ill.u.s.tration: Fig. 679.]

This lathe is constructed to accomplish the following ends. First, to have the lathe centres axially true with the work when grinding tapers, so that the lathe centres shall not wear and gradually throw the work out of true from the causes explained in the remarks on turning tapers in a lathe of ordinary construction.

Second, to have the headstock B capable of lateral swing, so as to enable the grinding of taper holes.