A chuck for a workpiece, rotatable in spaced relation to and about an axis of rotation, and having a clamp jaw radially movable under centrifugal force to engage the workpiece against fixed mating clamp members. The structure can also have optional means enabling the chuck to tilt, with the workpiece, from a home position to a preselected angle under the rotation thereof about a pivot axis perpendicular to and spaced from the axis of rotation with return of the chuck to the home position under gravitational force when rotation thereof is stopped.