Fig. 578.
An excellent example of an elevating rest for a weighted lathe is shown in [Figs. 577] and [578], which represent the construction in the Pratt and Whitney lathe. a is the lathe shears upon which slides the carriage provided with V slideways r for the sliding piece b, and provided at the other end with the guides h. The cross slide s is pivoted upon b at d, and fits at the other end between the guides h. At e is the elevating screw which when operated raises or lowers that end of the elevating rest to adjust the tool height. This also affords an excellent means of making a minute adjustment for depth of tool cut. The tool rest f is bolted to s.
The weight w is suspended from s and, therefore, holds one end of s to b, the lathe to c, and c to a; at the other end the weight holds s to c (through the medium of the elevating screw e) and c to a. The cross feed nut n is fast to s, the cross feed screw being operated by hand wheel g. b is provided with the V slideways r, which slide upon corresponding V slides r′ upon c; p is a lug cast upon c, and k is a screw threaded in b. When the end of screw k abuts against p the motion of s, and, therefore, of the cutting tool t, towards the work is arrested, hence when the tool is adjusted to the proper depth of cut, k is operated to abut firmly against p, and successive pieces may be turned to the same diameter without requiring each piece to be measured for diameter. n is the handle for opening and closing the nut for the feed screw q, and z is the wheel for the hand feed traverse. The length of cross feed motion is determined by the length of the cross V slides r′.
This class of rest possesses the advantage that no lost motion in the slides occurs by reason of the wear, because the weight keeps the parts in constant contact notwithstanding such wear; on the other hand, however, the slide Vs sustain the extra wear due to the weight w in addition to the weight of the carriage. Lathes of this class are intended for light work, and are less suited for boring than for plain turning; they are, however, very convenient, and are preferred by many to any other kind of lathe for short and light work.
Fig. 579.
