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Concentric clamping and compensating – “round stays round”

12 April 2007

Clamping of thin-walled workpieces and other components that can easily deform is the classic challenge in metal working. Conventional 3-Jaw-Chucks are achieving their capability limits quickly as the workpiece deforms under the affecting forces - making precise machining impossible. Schunk Intec is now offering the new 6-Jaw Power Chuck ROTA NCR as a sophisticated solution to this problem. The deformation of sensitive workpieces can be substantially reduced due to the 6 contact points of the Rota NCR. It delivers considerably improved concentricity that in turn allows precise machining. The jaws oscillate in pairs and this guarantees that centring pre-machined and noncircular components can be achieved with optimum accuracy. For customers meeting the challenge of clamping ring-shaped or asymmetric workpieces for machining – making a compromise on accuracy can now be a thing of the past. When selecting suitable clamping equipment for holding the workpiece safely with less deformation, this innovation from Schunk is the right solution. The Power Chuck ROTA NCR is equipped with a central chuck piston that incorporates three pendulum bodies that are supported by the chuck and aligned 120° to each other. Every pendulum body is connected with two base jaws resulting in a workpiece that centres between six contact points that can then be adjusted in pairs. The clamping forces are aligned with the chuck centre allowing pre-machined or asymmetric components to be centred without distortion of the workpiece. In tests, Schunk compared the values of roundness during machining on a conventional 3-Jaw chuck with those of a ROTA NCR chuck. Under the same testing conditions, the achieved roundness after machining with a 6-Jaw-Chuck was approximately eight to nine times more dimensionally accurate and round (reduced lobing effect) compared to the equivalent 3-Jaw chuck. The distribution of forces to six contact points affects the workpiece much more evenly and the workpiece deformation is considerably lower. SCHUNK Product Manager Markus Michelberger comments: “The chuck has proven its value and customers are already using the Rota NCR for alternative work for which the chuck was not originally designed. Time-consuming changeovers are eliminated and set-up times can be reduced considerably in many cases.” For certain applications such as finish machining or clamping of pre-turned workpieces, the pendulum bodies of the ROTA NCR can be fixed with a clamping screw into the centre position. In this configuration a simultaneous concentric movement of all six chuck jaws is assured. This way the workpiece is clamped concentrically without any compensation function. The Rota NCR can be equipped with matching chuck jaws from the vast Schunk standard chuck jaw programme. This has both cost and time saving benefits as no special solutions are now necessary. The functional components are hardened on all sides and ground to ensure the highest possible true-running and repeat accuracies. The low chuck height allows maximum use of the machine working space and guarantees maximum rigidity of the system. The ROTA NCR is offered as a standard version which is available in 165, 200, 250, 315, 400, 500, 630, 800 and 1000mm sizes. Alternatively the ROTA NCR chuck can be ordered with centrifugal force compensation. For actuation of the chuck, a standard clamping cylinder is employed.

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