[Fig. 1539] shows a circular table swivelled by the same device, sitting upon a work table also swivelled.
Fig. 1540.
[Fig. 1540] represents a general view of a shaping machine having the motion corresponding in effect to a planing machine, the object being to give a uniform rate of speed to the tool throughout, both on its cutting and return stroke. The feed always takes place at the end of the return stroke, so as to preserve the edge of the tool, and the length of the stroke may be varied, without stopping the machine, by simply adjusting the tappets or dogs, the range of stroke being variable from 1⁄4 inch to 20 inches, while the return stroke is 40 per cent. quicker than the cutting one. There are two different rates of cutting speed, one for steel and the other for the softer metals.
Fig. 1541.
The ram or bar is provided with a rack (z, [Fig. 1545]) which engages with a pinion s, [Fig. 1541], h being the driving shaft driven by the belt cones a and b. These two cones are driven by separate belts, but from the same counter-shaft, one being an open and the other a crossed belt. The open belt drives either the largest step of pulley b, giving a cutting speed suitable for steel, or the smaller step, giving a cutting speed for softer metals, as cast iron, &c. The crossed belt drives, in either case, the pulley a for the quick-return stroke, and this pulley revolve upon a sleeve or hub c, which revolves upon the shaft h. The sleeve or hub c is in one piece with a pulley c, whose diameter is such as to leave an annular opening between its face and the bore of the largest step of cone pulley b, and pulley a is fast to the hub or sleeve c. It will be seen that as the driving belts from the counter-shaft are one open and one crossed, therefore pulley a runs constantly in one direction, while pulley b runs constantly in the other, so that the direction of motion of the driving shaft h depends upon whether it is locked to pulley a or to pulley b.