| 摘要 |
PROBLEM TO BE SOLVED: To easily change or set the eccentric quantity of a main spindle to the rotation center axis by decentering the rotation center of a chuck holding member to the rotation center axis of the main spindle, and decentering the chuck of the chuck holding member from the rotation center axis of the chuck holding member. SOLUTION: A chuck holding member 64 is supported relatively rotatably on a main spindle 14 around the rotation center axis 66 relatively eccentric from the rotation center axis 24 of the main spindle 14 by a first eccentric quantity e1. The collet center axis 86 of the collet 64 of the chuck holding member 64 is set relatively eccentrically from the rotation center axis 66 of the chuck holding member 64 by a second eccentric quantity e2. When the chuck holding member 64 is rotated around the rotation center axis 66, the collet center axis 86 is displaced on a circumference with the diameter e2 around the rotation center axis 66.
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