Fig. 523.
[Fig. 523] is a sectional view of the carriage and slide rest as arranged for 12 and 16-inch lathes when not provided with a self-acting cross feed. In this case end motion to shaft c is given by lever h, which is held in its adjusted position by the tongue t. In this lathe the screw-cutting and the turning feed cannot be put into gear at the same time.
The tool nut is arranged to enable the tool to be adjusted for height after it is fastened in the tool post by pivoting it to the cross slide, a spring s forcing it upwards at its outer end, thus holding the tool point down and in the direction in which the pressure of the cut forces it, thus preventing the wear of the pivot from letting the tool move when it first meets the cut. The nut n is operated to adjust the tool height, and at the same time enables the depth of cut to be adjusted very minutely. A trough catches the water, cuttings, &c., and thus protects the slides and slideways from undue wear.
In all these lathes the feeding mechanism is so arranged that there are no overhanging or suspended shaft pins or spindles, each of such parts having a bearing at each end and not depending on the face surface of a collar or pin, as is common in many lathes. Furthermore, in these lathes the handle for the hand carriage feed moves to the right when the carriage moves to the right; the cross-feed screw (and the upper screw also in compound slide rests) has a left-hand thread, so that the nut being fixed the slides move in the same direction as though the nut moved as in ordinary lathes. The tailstock or poppet-head screw is a right hand because the nut moves in this case. The object of employing right-hand screws in some cases, and left-hand ones in others, is that it comes most natural in operating a screw to move it from right to left to unscrew, and from left to right to screw up a piece, this being the action of a right-hand screw, left-hand screws being comparatively rarely used in mechanism, save when to attain the object above referred to.
Fig. 524.
[Fig. 524] represents the Niles Tool Works car axle lathe, forming an example in which the work is driven from the middle of its length, leaving both ends free to be operated upon simultaneously by separate slide rests.
The work being driven from its centre enables it to rotate upon two dead centres, possessing the advantage that both being locked fast there is no liberty for the work to move, as is the case when an ordinary lathe having one live or running spindle is used, because in that case the live spindle must be held less firmly and rigidly than a dead centre, so as to avoid undue wear in the live spindle bearings; furthermore, the liability of the workman to neglect to properly adjust the bearings to take up the wear is avoided in the case of two dead centres, and no error can occur because of either of the centres running out of true, as may be the case with a rotating centre.
The cone pulley and back gear are here placed at the head of the lathe driving a shaft which runs between the lathe shears and drives a pinion which gears with the gear on the work driving head shown to stand on the middle of the shears. This head is hollow so that the axle passes through it. On the face of this gear is a Clement’s equalizing driver constructed upon the principle of that shown hereafter in [Fig. 756].