| 摘要 |
PURPOSE:To reduce the deformation of a cylindrical part in case of holding a chuck by providing a circumferential groove-shaped stepped part on a root position of a projecting part from the back part in the cylindrical part, and making the chuck having a fitting-in part to the stepped part generate a pressing component of force toward the back part. CONSTITUTION:A circumferential groove-shaped stepped part 8 is provided on a root position of a projecting part from a back part 2b in a cylindrical part 2c. A sectional shape of the stepped part 8 is an inverted trapezoidal shape, and the inside surface becomes a tapered surface 8a having an angle of theta degrees against the outside circumferential surface of the cylindrical part 2c. A three-way chuck 7 has a fitting-in part provided with a tapered part 7a corresponding to the tapered surface 8a, and when the stepped part 8 is held, a pressing component of force P2 in the cylindrical axis direction toward the back part 2b is generated by an action of the tapered surface 8a against its chuck pressure P1. Therefore, as for a total friction area of the three-way chuck 7 to a lower drum 2, in addition to a friction area to the tapered surface 8a by the tapered part 7a, a friction area to the back part 2b by the pressing component of force P2 is generated. Since the friction area increases remarkably, the holding force can be obtained by a small chuck pressure, and a deformation of the cylindrical part 2c is reduced. |
