Crank

Crank, in Mechanics, is a lever with one end grasping a rotating shaft, and the other end a connecting rod. Its usual purpose is to convert the alternating motion of the end of the connecting-rod into the rotating motion of the shaft. It is made generally of cast-iron, wrought iron, or of case-hardened steel. The connecting-rod grasps the crank by a cylindrical crank pin, which fits closely in a hollow cylindrical bearing or bush of softer metal, such as brass or gun metal. Such a lever is the single crank, which may be fitted on to the end of the shaft. If, however, the motion is to be given to a central portion of the shaft, a piece must be cut out of the latter, and a double crank fitted on, the general alternative being to fix on an eccentric (q.v.).