A diaphragm chuck assembly having clamping jaws disposed in a chuck body and in driven connection with a diaphragm deformable by an axially adjustable actuator, the clamping jaws having contact pieces, in which counterweights are disposed in recesses of the chuck body and the clamping jaws are clamped against the diaphragm by means of quick-clamping devices engaging in the contact pieces, the contact pieces being arranged in the diaphragm and in the counterweights with radial play. The clamping jaws are supported against a first surface extending axially in parallel to the chuck body in the clamping position and against a second reference surface extending at right angles to the first reference surface and into the diaphragm. The clamping jaws can be changed in a short time and the clamping jaws can be replaced without having to be reground.