On ordinary machine tools, the processing of thin-walled flanges with an outer diameter of 8 mm or less or thin-walled flanges with an inner diameter of 70 mm or less is limited by the thickness of the inner arc R of the jaws of the three-jaw chuck and the thickness of the external jaws of the jaws. At this time, the method shown in Figures 1 and 2 can be used to clamp a large three-claw chuck on the lathe.