Chuck with dual independently actuable sets of jaws

A chuck to hold a workpiece in a machine for spinning the workpiece about an axis and machining surfaces thereof, the chuck comprising:

• an annular body disposed in the machine and adapted to be rotatably driven thereby;
• a first set of at least three jaws movable radially inward from the annular body to grip the workpiece;
• a second set of at least three jaws movable radially inward from the annular body to grip the workpiece, the second set of jaws being axially displaced from the first set whereby the first set of jaws engages the workpiece at a first outer surface and the second set of jaws engages the workpiece at a second outer surface axially displaced from the first outer surface;
• first and second jaw set actuation means comprising, respectively, first and second sets of lead screws, one lead screw engaging each of the jaws and being effective to advance and withdraw the engaged jaw with rotation in opposite direction, first and second ring gears engaging all of the first and second sets, respectively, of lead screws, first and second fluid pressure motors actuably engaging the first and second ring gears, respectively, each fluid pressure motor having a piston in a chamber and being effective, upon admission of pressure fluid to one side of the piston, to rotate the associated ring gear in a direction to advance the associated set of jaws and, upon admission of pressure fluid to the opposite side of the piston, to rotate the associated ring gear in the opposite direction to withdraw the associated set of jaws, each of the second set of lead screws including a slip clutch effective to limit the force applied by the associated jaw to the workpiece, whereby all jaws of the second set can be advanced into engagement with the workpiece without shifting the workpiece axis;
• first and second locking means associated with the first and second sets of jaws, respectively, the first and second locking means comprising, respectively, first and second sets of collars, one of the collars being associated and engageable with each lead screw, first and second sets of lock members, one of the lock members being associated and engageable with each collar to transmit a locking force through the associated collar and lead screw to bias the associated jaw against the workpiece, first and second locking spring means associated with the first and second set of lock members, respectively, and effective to bias the associated sets of lock members in the direction of engagement with the associated collars, and third and fourth fluid pressure motors separately actuable to exert force opposing the first and second locking spring means, respectively, to release the locking force of the first or second set of jaws from the workpiece;
• means for applying fluid under pressure selectively to the fluid pressure motors, whereby the workpiece can be gripped by the first set of jaws and rotated about the workpiece axis for machining of surfaces including the second outer surface, then with continuing rotation the workpiece can be gripped by the second set of jaws and released by the first set of jaws for machining on the first surface.