Clamping head with a large opening width

The invention relates to a clamping head with a large opening width for rotationally symmetrical workpieces, in which the clamping diameter is smaller than the largest outside diameter. The aim of the invention is to develop a clamping head which, whilst having high clamping accuracy, allows a large opening width and an automated work cycle in the piercing process. The object on which the invention is based is, by using the collet tension, to design a clamping head which, in the piercing process, clamps pin-shaped, but also stepped rotationally symmetrical workpieces. This object is achieved, according to the invention, in that guide pieces are fastened positively to the half-shells of the clamping collet and are each connected to a pin which is guided in radially rising grooves of a setting disc, the guide pieces being supported by a spring-loaded disc. After the return stroke of the thrust piece by > 2 s, the spring-loaded disc together with the guide pieces is displaceable over the distance > s until it comes to bear against guide bodies fixed in the supporting cap. In the stop position, the guide pieces are axially limited by the spring-loaded disc and the setting disc and, during the rotation of the setting disc, are radially adjustable between two guide bodies via a rotary body designed as a pawl wheel.