This invention relates in general to chucks for holding tools and in particular to a new and useful power operated chuck which includes radially movable clamping jaws.
Such power chucks, also termed wedge hook chucks, are known in a variety of designs and have proved satisfactory in practice. To equalize the centrifugal forces produced in the clamping jaws at high speeds and reduce an inwardly directed static clamping force or considerably augment an outwardly directed clamping force, it is known to provide balancing elements which are guided in the chuck body as counterweights and operatively connected to the jaws through hinged levers. The principal drawback of these constructions is that the static clamping forces acting on the clamped workpiece before and after a machining operation are not equal to each other and differ sometimes considerably. That is, as the chuck rotates at high speeds, the clamping force transmitted from the clamping piston through the wedge hooks to the jaws becomes almost counterweighted by the produced centrifugal forces and the elasticity of the coupled parts. Then, a part of the clamping force is produced by the balancing elements which are connected to the jaws through reversing levers. The clamping piston coupled to the jaws through the mating surfaces of the wedge hooks is thereby relieved and displaced, even though very little, by the action of a connected servo-mechanism which continues to be effective. In addition, the centrifugal forces expand the chuck body, so that the bore receiving the clamping piston is enlarged, with the result that the no longer backed-up wedge hooks can yield, which causes a further displacement of the clamping piston. However, after a machining operation is terminated, the chuck body contracts again, whereby the wedge hooks are pressed inwardly and the clamping force on the workpiece is augmented since the clamping piston does not retract, it is held fast in its displaced position. In consequence, the clamping force may increase considerably and often leads to a deformation of the workpiece.