Fig. 566.
In many American lathes the construction of the gearing that conveys motion from the live spindle is such that facility is afforded to throw the change gears out of action when the lathe is running fast, as for polishing purposes, so as to save the teeth from wear. Means are also provided to reverse the direction of lead screw or feed screw revolution. An example of a common construction of this kind is shown in [Fig. 565], in which the driving wheel a is on the inner side of the back bearing as shown. It drives (when in gear) a pair of gears, one only of which is seen in the figure at b, which drives c, and through r, d, i, and s, the lead screw. A side view of the wheel a and the mechanism in connection therewith is shown in [Fig. 566], in which s represents the live spindle and r is a spindle or shaft corresponding to r in [Fig. 565]. l is a lever pivoted upon r and carrying two pinions b and e; pinion b is of larger diameter than e, so that b gears with both c and e (c corresponding to wheel c in [Fig. 565]), while e gears with b only.
Fig. 567.
With the lever l in the position shown, neither b nor e engages with a, hence they are at rest; but if lever l be raised as in [Fig. 567], b will gear with wheels a and c, and motion will be conveyed from a to c, wheel e running as an idle wheel, thus c will revolve in the same direction as the lathe spindle.
