Patent ID: 8491357

Claim:
A method of machining a crankshaft having at least one main-bearing surface centered on a workpiece axis and first and second crankpin surfaces centered on respective crankpin axes parallel to but offset from the workpiece axis and angularly offset from each other, the method comprising the steps of sequentially: a) securing the crankshaft at its ends in respective first and second grippers of first and second holders rotatable about a common grinding axis, the first and second grippers being shiftable on the respective holders in respective first and second directions radial of the grinding axis; b) orienting the first and second grippers such that the workpiece axis is coaxial with the grinding axis; c) releasing the crankshaft from the first gripper; d) while gripping the crankshaft with the second gripper, rotating the second holder with the crankshaft to align the first crankpin with the first radial displacement direction of the first gripper; d′) regripping the crankshaft with the first gripper; e) while gripping the crankshaft with the first gripper, releasing the crankshaft from the second gripper and rotating the second holder relative to the crankshaft until the second holder is aligned with its second radial displacement direction lying in a common plane with the grinding axis and the first radial displacement direction of the first gripper; e′) regripping the crankshaft with the second gripper; f) shifting both the grippers parallel to each other in their displacement directions to center the first crankpin on the grinding axis; and g) rotating the crankshaft about the grinding axis while machining the first crankpin.