| 摘要 |
PROBLEM TO BE SOLVED: To position a work with high accuracy on the basis of a reference shape part such as a hole, eliminate a finishing process after end face turning to simplify the machining processes. SOLUTION: A main jaw 6 is assembled to a chuck body 1 so that it can move in the radial direction, and an upper jaw 7 is supported in the main jaw 6 so that it can move relative to the main jaw in the same direction. Levers 23, 24 are supported in the upper jaw 7 so that they can move radially and are energized to the outer peripheral side by a tension spring 37. When the main jaw 6 is closed, a holding part 17 of the upper jaw 7 strikes the outer peripheral surface of a ball gage W to stop the upper jaw 7, and an operating pin 39 of the main jaw 6 opens the levers 23, 24 by a relative motion between the main jaw 6 and the upper jaw 7. Positioning parts 23a, 24a directly hold a window-opening H to position the ball gage W in the axial direction on the basis of a center line of the window-opening. The main jaw 6 is further moved to the center side, and the holding part 17 holds the ball gage W from the radial direction. In this state, the end face is turned to obtain accurate dimensions of the position of a window.
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