[Fig. 493] represents a cross-sectional view of the shears beneath the headstock; a a are the shears or bed having the raised Vs marked v′ and v on which the headstock and tailstock rest, and v′′ and v′′′ on which the carriage slides. a and a′ are the shears connected at intervals by cross girts or webs b to stiffen them. c c are the bolts to secure the headstock to the shears. d is a bracket bolted to a′ and affording at e journal bearing for the spindle that operates the independent feed spindle. e is split at f and a piece of soft wood or similar compressible material is inserted in the split. The bolt f is operated to close the split, and, therefore, to adjust the bore e to properly fit the journal of the feed spindle, and as similar means are provided in various parts of the lathe to adjust the fits of journals and bearings the advantages of the system may here be pointed out. First, then, the fit of the bearing may be adjusted by simply operating the screw, and, therefore, without either disconnecting the parts or performing any fitting operation, as by filing. Secondly, the presence of the wood prevents the ingress of dust, &c., which would cause the bearings and journals to abrade; and, thirdly, the compression of the wood causes a resistance and pressure on the adjusting screw thread, which pressure serves to lock it and prevent it from loosening back of itself, as such screws are otherwise apt to do.

As the pressure of the tool cut falls mainly on the front side of the carriage, and as the weight of the carriage itself is greatest on that side, the wear is greatest; this is counteracted by forming the front V, marked v′′′ in [figure], at a less acute angle, which gives it more wearing area and causes the rest to lower less under a given amount of wear.

The rib a′′ which is introduced to strengthen the shears against torsional strains, extends the full length of the shears.

[Large
image
(96 kB).]

Fig. 494.

Fig. 495.