It should be cited that two sets of ways are frequent-ly provided for this reason ; the head and tail stocks are mounted on one set, which are never worn to any extent and therefore always remain in line and truer while the carriage travels on the other set, in which the wear is evident, but, since it is in a vertical direction to a great extent, the point of the tool does not travel very far from a straight line parallel with the centers.

The headstock, e, is bolted firmly to the bed, gener-ally resting on one of two sets of Vs. This stock car-ries the spindle, h, which runs in the bearings, i and i. The spindle is usually hollow to admit of rod stock being run through it to a chuck. The end at j is provided with threads and a shoulder against which the various pieces may jamb when screwed into place. The thrust of the work and tool against the spindle is taken up either by a thrust bearing surrounding the spindle at the back end, or by a yoke and thrust screw, as shown at k. This screw is also provided with an axial hole through which rod stock may be passed. This form, however, is rapidly being supplanted, especially in the smaller forms, and it is rarely seen except in some very large lathes. It has many points of advantager however, and leaves the bearings of the spindle free of all thrust loads.

The spindle should be as heavy as convenient, and should be supported in large bearings, especially at the head. This bearing, i, takes all the inducing chatter. Then, again, this bearing is largely responsible for the alignment of the lathe and any wear that takes place here will soon throw the entire machine out of commission for accurate, work. It is very seldom, except in cases where the belt pulls down, that any great wear occurs in the bottom half of the bearing. The belt generally pulls upwards and the tool thrusts the work upwards so that the top half of the bearing receives most of the wear. The bearing at the opposite end of the spindle is not subject to such great strains and, therefore, does not wear rapidly. The spindle, m, carries two gears in most cases, a large one, 1, at the head end, and a small one, m, at the opposite end. The gear, 1, is invariably keyed securely to the spindle, as the latter is driven by it at all times.

Mounted upon this spindle is the cone-pulley, n, to the small end of which is keyed a small pinion, o. This cone is free to revolve upon the spindle, and can be rigidly connected to the spindle only by means of a sliding bolt at p. This sliding bolt takes different forms; in some instances it is made to push in or pull out, and is then very convenient. With the ordinary bolt a wrench is necessary, and by sliding it in or out of a "notch in the inner periphery of the cone, a positive driving connection is made.

Owing to the fact that the countershaft turns at a constant speed, it becomes necessary to have some device whereby the speed of the spindle may be altered at will. As the diameter of the work increases, the speed will have to be reduced to maintain the cutting speed found best for that material. In order that this end may be readily accomplished, two opposed cone pulleys are used and so arranged that the largest step of one drives onto the smallest step of the other. By this method, the mere shifting of the belt from one step to another will give quite a variation of speed. Many of the light lathes and most all speed lathes are fitted with this cone only, but in lathes intended for heavy service and a greater range of work, it becomes necessary to provide more changes in speed, and to this end another spindle carrying a large and small gear is supported directly behind the main spindle. The large gear, q, meshes with the small pinion, o, and the smaller pinion on the "back-gear " shaf t meshes with the gear, I. These gears may be thrown in or out of mesh by means of a small eccentric journal on the end of a shaft, and this shaft is turned by means of a small handle, r.

The ratio of these back-gears is such that the same arithmetical proportion is preserved throughout the entire series of belt positions and, as in the case of the lathe shown, there would be four speeds with the cone connected directly to the gear, 1, and four slower speeds with the back gears thrown in. Of course the bolt, p, must be withdrawn from its slot when the back gears are thrown into mesh.

The end, h, is shown in Fig. 1, carrying a small driver plate, which is provided with one or more slots into which the tail of a "carrier" or " dog " enters, so that the motion of the spindle may be transmitted to the work, being turned on the centers, s and s'. A large face-plate, t, is also provided, which screws onto the spindle, in place of the small carrier plate, u. Chucks and other fixtures may be fitted to this threaded end.

At this point it may be well to give a few words of caution regarding the use and abuse of this thread. Too many lathe hands are careless in this respect, and it is a vital point in any lathe. In the first place, before screwing any fixture onto the spindle, see that the threads are perfectly clean; wipe them out with a little oil on a piece of waste, using a small stick of wood instead of any metal to force the waste into the groove. Then be equally sure that the thread in the face-plate, chuck or carrier is equally clean; also that the seat against which these parts rest are clean, as a small chip may throw any one of them out of alignment. When any one of them is put away, be sure to fill the threaded hole full of cotton waste which will keep out all dirt. If the pieces are to behung up, use a wooden peg rather than one of metal, as the latter mars the threads. Thus, with careful use, the fit of these attachments to the lathe spindle should remain accurate for years.

The tail-stock, f, is usually made in two pieces; a v, and the head, w. The base v is fitted to the inner set Vs in a manner similar to that used in the head-stock, except that it is free to move from one end of the lathe to the other. It is clamped in any particular position by means of the bolt, y, which passes into a clamping yoke beneath the upper flanges.

The head, w, is fitted to the base by means of a tongue-and-groove joint, z, which insures perfect parallelism, no matter what positions the two parts as-sume. A small screw, 1, serves to move the parts from one side to the other. This lateral movement is provided in order that tapers may be turned. The tail-stock is set to one side of the center line, and since the tool moves in a straight line, it will gradually approach nearer to one center than the other, thus making a gradual reduction in the diameter of the piece being turned. In many of the modern lathes this is rendered unnecessary by a taper attatchment fixed to the back of the lathe. It is simply a grooved piece so supported that it may be set at any angle, within small limits, with the centerline of the lathe. In this groove slides a block to which is attached the tool-post block. The tool is therefore constrained to move in a line at a defi-nite angle with the axis of the work which forms the taper. This attachment is far superior to the method of setting over the tail-center, as the work revolves upon a perfectly fitted cone, and not on one side of it. As a general rule, a more abrupt taper may be turned with this attachment, and it is especially handy when the taper occurs in the middle of along piece, as it then becomes very difficult to set the tail-stock over far enough.

This stock also carries a spindle, called the "tail-spindle " the end of which is shown at 2. This spindle-is free to move in a longitudinal direction, but a key in the stock ban-el prevents its rotation. A taper socket is provided which accommodates the centers' or an-other attachment that may be desired. A hand-wheel, serves to move the spindle in or out, and it is clamped in position by some such device as the cam, 4, or a clamping screw. As there is little movement in this spindle, it does not wear to any great extent. It, should be very solid, however, as lack of rigidity at this point will quickly induce chattering.

The tool carriage next claims our attention. The carriage proper rests upon the outer set of Vs, and is provided with very long bearings so that the wear may be reduced to a minimum. The bridge connecting the two bearings is provided with Vs, 5, upon which the tool block, 6, is mounted. This block, which carries the tool, 7, is moved by the screw, 8, of which only the-handle is visible. A modification that is often made made of the plain rest is that shown in Fig. 1 and known as the compound rest. It is simply another slide mounted on the tool block, the slide, 9, being moved by the screw, 10. This slide may be set at any angle and the tool thus fed to the work along any line at any angle to the plane of the face-plate or center-line of the lathe. It is almost indispensable in a general line of work, as tapered holes may be bored with it and very short tapers turned. The base, 11, is generally provided with a graduated arc by means of which the exact angle being turned may be determined.

The carriage is fed along the ways by means of a feed screw, 12. This screw is driven by gearing in this case, but usually a belt is used, as breakage is often prevented under an overload by the belt slipping. The thread of the screw is seldom, and should never, be used for ordinary feeding, as its purpose is that of . thread cutting, and the greater the wear therein the less accurate will be the thread cut. A key-way or "spline " is usually cut throughout the entire length of this screw, into which fits a key in a sleeve surrounding screw 12. The rotation of 12 then turns this sleeve, the periphery of which is provided with a worm thread. This in turn drives a gear that meshes with the rack, 13, and any motion of the gear will cause the carriage to move along the bed. This gear may be thrown in or out at will by the thumb-nut, 14, which controls a friction clutch behind the apron, 15. For ordinary feeding by hand, and rapid movement of the carriage, the hand-wheel, 16, which is connected with the rack-gear by means of an intermediate pinion, is used.

In order that the screw, 12, may be used for thread cutting, a means for attaching the carriage thereto must be provided, and this is accomplished with a spit that closes over the screw by means of the handle , 17. Another set of gears, behind the apron, are thrown into gear by the friction clutch nut, 24, and feed the tool across the carriage, giving what is known as automatic cross feed. A lever, 18, is provided on many lathes for reversing the direction of feed at the apron, and is very convenient. Still others incorporate this attachment as a part of the head-stock mechanism.

The matter of the change gear, compound gearing, thread cutting and the use of special attachments will be taken up in later chapters.