In g is a radial slot through which passes a bolt i provided with a cap nut h, in m is an annular groove j. When i is lifted its head passes into a recess in m, then h is screwed up and g is locked to m. This is the position of i when the back gear is not in use, the motion of the cone being communicated to s through i. But if h be loosened and i be moved inwards towards s, the head of i passes into the annular groove j, and the cone is free to rotate upon s while the latter and g remain stationary unless the back gear is put into operation. In this latter case the pinion g′ rotating with the cone drives the large gear of the back gear and the small pinion of the latter drives g, whose speed of rotation is reduced by reason of the relative proportions of the gear wheels.
In this case it is obvious that since the pulley rotates upon the spindle it requires lubrication, which is accomplished through the oil hole tubes l.
The means of giving motion to the feed spindle and lead screw are as follows:—n, [Fig. 494], is a pinion fast upon s and operating the gear o, which is fast upon the spindle p, having journal bearing in a stem in a′ and also at g′′. p drives the three-stepped cone r, which is connected by belt to a similar cone fast upon the independent feed spindle. The seat for the driving gear of the change wheels for the lead screw is on p at v. To provide ample bearing surface for p in a′ the bush or sleeve shown is employed, but this sleeve also serves to pivot the swing frame w which carries the studs for the change wheels that go between the wheel on v and that on the lead screw; x y are simply oil holes to lubricate p in its bearings.
To provide a wider range of tool feed than that obtainable by the steps on the feed cones, as r, they are provided at their ends with seats for change wheels, the swing frame w carrying the intermediate wheels for transmitting motion from v to a similar seat on the cone on the feed spindle.
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Fig. 497.
[Fig. 497] represents the tailstock (or tailblock as it is sometimes termed), shown in section. a represents the base which slides upon the raised Vs on the bed and carries the upper part b, in which slides the tail spindle c, which is operated longitudinally by the tail screw d, having journal bearing in e, and threaded through the nut f which is fast in c. The hand wheel g is for rotating d, whose thread operating in the nut f, causes c to slide within b in a direction determined by the direction of rotation of g. To lock c in its adjusted position the handled nut h is employed in connection with the bolt i, which is shown in dotted lines; c is split as shown by the dotted lines at f; j is the dead centre fitting accurately into a conical hole in c. When it is required to remove j from c the wheel g is operated to withdraw c entirely within b, and the end d of d meets the end e of j and forces j from the coned hole in c.
The method of securing the tailstock to the shears or releasing it from the same is as follows. A vertical prolongation of b affords at b′′ a bearing surface for the nut-handle l and washer m. k is a bolt threaded into l passing through m, b′′ and n, the latter of which it carries. n spans the shears beneath the two Vs on which the tailstock slides. Moving or rather partly rotating the handle l in the necessary direction lifts k and causes n to rise, and grip the shears beneath, while the pressure of m on b′′ causes b to grip a and the latter to grip the raised Vs on the shears. If l be rotated in the opposite direction it will cause n to fall, leaving a free to slide along the shears. To prevent n from partly rotating when free, its ends are shaped to fit loosely between the shears as shown at n.