Crank (mechanism)

A crank is an arm attached at a right angle to a rotating shaft by which circular motion is imparted to or received from the shaft. When combined with a connecting rod, it can be used to convert circular motion into reciprocating motion, or vice versa. The arm may be a bent portion of the shaft, or a separate arm or disk attached to it. Attached to the end of the crank by a pivot is a rod, usually called a connecting rod (conrod). The term often refers to a human-powered crank which is used to manually turn an axle, as in a bicycle crankset or a brace and bit drill. In this case a person's arm or leg serves as the connecting rod, applying reciprocating force to the crank. There is usually a bar perpendicular to the other end of the arm, often with a freely rotatable handle or pedal attached. Familiar examples include: Spinning wheel Mechanical pencil sharpener Fishing reel and other reels for cables, wires, ropes, etc. Starting Handle for older cars Manually operated car window The carpenter's brace is a compound crank. The crank set that drives a handcycle through its handles. Hand winches The crankset that drives a bicycle via the pedals. Treadle sewing machine Almost all reciprocating engines use cranks (with connecting rods) to transform the back-and-forth motion of the pistons into rotary motion. The cranks are incorporated into a crankshaft. Science and technology of the Han dynasty It was thought that evidence of the earliest true crank handle was found in a Han era glazed-earthenware tomb model of an agricultural winnowing fan dated no later than 200 AD, but since then a series of similar pottery models with crank operated winnowing fans were unearthed, with one of them dating back to the Western Han dynasty (202 BC - 9 AD). Historian Lynn White stated that the Chinese crank was 'not given the impulse to change reciprocating to circular motion in other contrivances', citing one reference to a Chinese crank-and-connecting rod dating to 1462.