Cranks.
(‡ Knife-Grinder.)
Cranks are bends in the axle of any part of a machine by which an up-and-down motion is converted into a circular or rotatory one, as in the common knife grinder’s machine; in this arrangement a fly-wheel is necessary to continue by its momentum (tendency to go on) the motion begun by the upward and downward action of the treadle, piston-rod, &c., as the case may be. The cranks of steam-vessels are among the heaviest pieces of forging that are wrought by Nasmyth’s steam hammer, cast-iron being too brittle to be used for the purpose.