Arrangement of mechanical parts used to obtain a reciprocating straight-line motion from a rotating shaft.
It serves the same purpose as a slider-crank mechanism and is particularly useful when the required stroke of the reciprocating motion is small in comparison with the dimensions of the driving shaft. Because an eccentric can be attached anywhere along a shaft, it is unnecessary to form any part of the shaft into a crank . Eccentrics are seldom used to transmit large forces because friction loss would be high; they are commonly used to drive the valve gears of engines.