How the key bar chucks of the DURO-T series work

Operating principle

Thanks to the tangentially arranged threaded spindle (1), the force is transferred via a key bar (2) having an internal thread. The key bar moves the drive ring via a slide (3). Two other slides in the drive ring (4) transfer the forces to the other two key bars. The key bars having an inclined profile engage in the base jaws (5), thereby guaranteeing exact, centric clamping. The jaws can be quickly and easily turned, changed or offset over the entire clamping range within a few seconds. To do this, the key bars must be disengaged by turning the key to the left; the indicator pin (6) will project here. In this position, the jaws are secured against being hurled out in the event the machine spindle is started up unintentionally. Therefore, the gate valve (7) of each jaw must be unlocked via the corresponding pressure bolt (8) on the outer diameter of the chuck.  Large, straight-line force transfer surfaces between the key bar and jaw toothing yield a very high clamping force over a long service life and with precision that is twice as high as prescribed by DIN 6386. The high clamping force is achieved without exerting any special amount of force by manually turning the key.


To maintain the clamping force, key bar chucks must be lubricated regularly. You will find corresponding information in the operating instructions, which are enclosed with every chuck. For easy maintenance, DURO-T chucks are equipped with three additional grease nipples on the front side.