A chuck assembly for supporting cylindrically shaped workpieces to be machined at their ends, the assembly comprising a body having a passage in its lengthways axis, a driving for providing an actuation force absorbed by an actuating pin axially movable in the body, a guide hole in the body having the actuating pin therein, and centring jaws, mounted in a guide groove in the chuck body and moveable radially toward the workpiece, each in a driving arrangement an actuating pin. A roller provided on the driving means facing the actuating pin, a contact surface is on a free end of the pin at right angles to the lengthways axis of the chuck body. The contact surface and the roller interacting such that forces of driving means transfer onto the contact surface axially, and simultaneously a movement at right angles to the lengthways axis of the chuck body is released between the contact surface of the actuating pin and the roller.