Heavy-duty chuck

Claim 1

In a chuck, the combination with a plurality of companion jaws, and a chuck body carrying jaws of which at least one jaw is mounted for movement to bring work to and from gripping engagement with said jaws, of a drive for moving said one jaw, including a unit having companion screw and nut parts with a common axis and bearing balls, said screw and nut parts having outer and inner helical races, respectively, for said balls, with said nut part having also a ball return passage between axially spaced portions of said inner race to form with the latter an endless ball path, one of said parts being mounted in said body against rotation about, but for movement in the direction of, said axis, and the other part being mounted for rotation about, but against movement in the direction of, said axis, an operative connection between said one part and said one jaw to move the latter on axial movement of said one part, means for applying torque to said other part, and means locking said other part against rotational give under any applied work-gripping force of said one jaw, comprising a thrust end surface on said other part and a fixed thrust takeup surface in said body, with said other part having limited axial play and said surfaces being of materials of high coefficients of friction, so that on thrust exertion of said one jaw against work and ensuing backup of said other part with its thrust end surface into forced engagement with said thrust takeup surface said surfaces will serve as a brake against rotational give of said other part.