Shaft bearing on a machine tool

A shaft bearing on a machine tool for mounting a shaft end of a rotating workpiece to be machined, said shaft bearing comprising a rotatably mounted clamping chuck for clamping the shaft end and having a plurality of gripping parts which are mounted in a hollow clamping head so as to be radially adjustable relative to a longitudinal axis of the machine tool, wherein each of said plurality of gripping parts is mounted rotatably about a pivot axis extending parallel to a longitudinal axis of the clamping head and is guided, in a region distant from the pivot axis, along a guide track formed on a guide element and is movable relative to the associated guide track for clamping said shaft end of said workpiece, wherein the guide tracks are arcuately curved and extend about the longitudinal axis of the clamping head at a decreasing distance from the longitudinal axis of the clamping head, and wherein each gripping part is guided by a pin which engages a guide groove extending laterally relative to the gripping parts and approximately parallel to the guide track and which is arranged parallel to the pivot axis of the gripping part.