Crank

(krangk.) [A.S. crang.] (Mech.) An important contrivance in the proce of converting a rectilinear motion, as that of the piston in asteam-engine, into a motion of rotation. It consists usually of a double winch, but sometimes is only single. That part between the two elbow joints is termed the arm of the crank. The connecting-rod which transmits the alternate motion due to the power is attached to the cra uk by a joint, and consequently is made to traverse the circumference ofa circle of which the arm is the radius, and so to produce the rotation of the axis. The connecting-rod has its greatest effect in turning the crank about its axis only when it is at right angles to the arms; and in every other position, a portion of its force is spent in pulling the crank away from the axle. [s. 240]