If the motion from a to i was continuous, the carriage feed or traverse would be continuous, but means are provided whereby motion from f to i may be discontinued, as follows:—A hand traverse or feed is provided. j, [Figs. 575] and [576], is carried by a stud having journal bearing in a hub on x and receiving the handle q; hence by operating q, j is rotated, operating the gear h, upon which is the pinion i, which is in gear with the rack running along the lathe bed.
To lock the carriage in a fixed position, as is necessary when operating the cross feed on large radial surfaces, the following device is provided:—n is a stud fixed in a hub on x, and having a head which overlaps the rim of h, as shown in figure. On the other side of that rim is a washer z on the same stud having a radial face also overlapping the rim of h, but its back face is bevelled to a corresponding bevel on the radial face on the hub of lever o (the hub of o being pivoted on the same stud). When therefore o is depressed the two-bevel face of the hub of o forces the washer z against the face of the wheel h, whose radial faces at the rim are therefore gripped between the face of the collar n and that of the washer z, hence h is locked fast. By raising the end of lever o, z is released and h is free to rotate.
Both the carriage feed and cross feed can only be traversed in one direction so far as these gears and levers are concerned, but means are provided on the lathe headstock for reversing the direction of motion of the feed spindle f so as to reverse the direction of the feeds. It will be observed that so long as f rotates, a, c, d, and f rotate, the remaining motions only operating when s is screwed up.
In order to obtain a delicate tool motion from the handle q it is necessary to reduce the motion between j and i as much as possible, a point in which a great many lathes as at present constructed are deficient, because q, although used to simply traverse the carriage along the bed, in which case rapid motion of the latter is desirable, is also used to feed the tool into corners when the lathe has no compound rest to put on light cuts on radial faces, hence it should be capable of giving a delicate tool motion.
On account of the deficiency referred to it is often necessary to put on a fine radial cut by putting the feed traverse in gear, and, throwing the feed screw gear out of contact with the other change wheels, pull it around by hand to put on the cut. In compound slide rests these remarks do not apply, because the upper part of the rest may be used instead of the handle q.
Many small lathes are provided with a tool rest known as the elevating rest, or weighted lathe.
Fig. 577.