| 摘要 |
PROBLEM TO BE SOLVED: To provide a chuck mechanism for a hand piece capable of having simple structure, and reducing the cost of the hand piece. SOLUTION: A short diameter part, having a diameter relatively shorter than that of a long diameter part, is set to the inner periphery of a rear spindle diameter-expanded part 22', three chuck pins 30 and a pin holding member 31 are housed in the diameter-expanded part, the respective chuck pins are housed in the pin housing part of the pin holding member 31, and the member 31 is diameter-shortened by one coil spring 34. In an unused condition of a bar 1 mounted on a hand piece 10, the respective chuck pins are positioned in the long diameter part in the diameter expanded part, and the movement of the bar to a spindle 20 can be allowed only when the chuck pin 30 exist in this position. Since when a spindle 20 is rotated, rotation directional force is applied to the bar by frictional force via the respective chuck pins, and also the member 31 too begins to rotate in the same direction, the chuck pin 30 is deviated to the short diameter part in the inner side from the long diameter part of the diameter expanded part, to act so as to press the bar outer periphery, thereby fixing the bar 1 being in a use condition.
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