A rotary workpiece such as a camshaft is to be mounted in a work holder and is to be treated at two or more axially spaced locations. The workpiece can be simultaneously treated by driven abrasive belts which are mounted on two or more discrete carriages or by one of two belts on a common carriage.The belts (36,37) on a common carriage (18) can be selected to effect coarse and precision grinding of selected portions of the rotary workpiece (7) in the work holder. While a first shoe (38) urges one of the belts on the carriage (18) into material removing engagement with the workpiece, a second shoe (39) for the other belt is maintained in a retracted position in which the belt is out of contact with the workpiece.
