Rotary chuck for a machine tool

A rotary chuck of the type including a housing for rotation about a housing axis, a plurality of keyways formed in the housing, said keyways being angularly spaced around, and extending radially away from, said axis, a corresponding plurality of jaw assemblies slidably received in the keyways and an actuatuing mechanism having a selected gear ratio for moving the jaw assemblies along their respective keyways simultaneously between radially inner and outer positions characterized in that each jaw assembly comprises

• an inner jaw including a key portion keyed to the associated keyway adjacent to a bottom thereof;
• an outer jaw including a key portion keyed to the associated keyway near a mouth thereof so that said inner and outer jaws can slide independently along the associated keyway, said outer jaw also having a clamping portion projecting from the associated keyway in the general direction of said axis for engaging a workpiece;
• a locking device for releasably locking the inner and outer jaws together when is they are opposite one another to prevent their relative movement along the associated keyway, and
• means enabling release of the locking device from the outside so that the outer jaw can be moved relative to the inner jaw away from said axis and slid out of the associated keyway.