The crankshaft is also called as crank, it is the part of an engine which changes the up and down motion of the pistons into rotational motion. The crankshaft has one or more equal shafts to transform it into motion. Through these shafts the pistons are connected to the crankshaft. When the piston moves in rotational motion, it moves the offset shaft. This in turn spin the crankshaft. The crankshafts are normally made from metal, with most modern crankshafts being composed using forged steel. The crankpins rotate within the connecting rods using rod bearings, and the crankshaft rotates within the engine block through use of main bearings. Crankshafts are consist of a list of cranks and crankpins to which the connecting rods are connected. Crankshafts they are normally used in internal combustion engines. To develop the fatigue strength, a radius is generally rolled at the ends of each main and crankpin bearing. The radius by itself overcome the stress in these critical areas, but since the radius in most cases is rolled, this also leaves some compressive residual stress in the surface, which forbid cracks from building.