Abstract: A work holder for precision positioning and movement of a workpiece (20) relative to a machine tool comprises a base (100), a pair of spaced stocks (200, 300) mounted on the base, a spindle assemblies (210, 310) supported on each of the stocks for rotation about a common axis, a chuck (246, 346) supported on each of the spindle assembly (210, 310) for clamping the workpiece (20) therebetween, and adjustable mounting means (236-272, 336-372) on each of the spindle assemblies (210, 310) for permitting movement of each of the chucks (246, 346) transversely of the axis. A driveshaft (406) and gearing (402, 408) is provided for imparting rotation to one spindle assembly (210). A crank (422) is operatively connected to the driveshaft (406), and oscillating drive means (416) is providing for oscillating the crank (422) about the driveshaft (406) in two opposite directions.