Clamping chuck and key rod therefor

A powered clamping chuck for machine tools, in particular for lathes, having a chuck body (1) and several clamping jaws (4) that are arranged movably in radial jaw guides (3) of the chuck body (1) and are displaceable together, by means of a drive, radially with respect to the chuck axis (A), the drive including key bars (5) that are slidably guided transversely to the chuck axis (A) for displacement of the clamping jaws (4) in the chuck body (1) and each comprise a tooth set (7) that is in engagement with a corresponding counter-tooth set (8) on an associated clamping jaw (4);

• a positioning mechanism being provided that comprises a releasing bolt (P) mounted rotatably in the chuck body (1) and a releasing key (S) that can be coupled to the releasing bolt (P) in order to displace, by way of a rotation of the releasing bolt (P), the key bar (5) or a coupling attachment (5b), comprising the tooth set (7), of the key bar (5) parallel to the chuck axis (A) between an upper working position and a lower jaw changing position in which the tooth set (7) of the key bar (5) is pulled back out of the counter-tooth set (8) of the clamping jaw (4) and the latter can be removed radially from the chuck body;
• and a locking device being provided which locks the releasing key (S) on the releasing bolt (P) and permits disengagement of the releasing key (S) only in the working position of the key bar (5),
• wherein the key bar (5) has locking means that allow a rotation of the releasing bolt (P) out of the rotational position corresponding to the lower jaw changing position of the key bar (5), into the rotational position corresponding to the upper working position of the key bar (5), if the tooth set (7) of the coupling attachment (5b) is in engagement with the counter-tooth set (8) of an associated clamping jaw (4), and that otherwise prevent rotation of the releasing bolt (P) into the rotational position corresponding to the upper working position.