| 摘要 |
PURPOSE:To eliminate a mistake in chucking by forming in about same dimension the gap between the outer periphery at the tip part of a spindle shaft and the inner periphery of an annular wall and the gap between the outer periphery at the tip of the spindle shaft and the plane part of the annular wall with the gap between the lower case center hole and the annular wall outer periphery being in uniform state. CONSTITUTION:A pair of plane parts 12a, 12b in V shape are formed on the inner peripheral face of the annular wall 12 engaged with a spindle shaft tip 18 and centering is effected with this face abutting to the outer periphery of the spindle shaft. The gap between the outer periphery of the tip part 18 of the spindle shaft and the plane part of the annular wall and the gap between the outer periphery of the spindle shaft tip part 18 and the inner periphery 12d of the annular wall 12 can be uniformized by moving in the apex direction of the V-shaped plane part to the extent of about 1/4 of the difference in the outer diameter of the spindle shaft tip part 18 and the inner diameter of the circle in cribing to the plane parts 12a, 12b of the annular wall 12 the center of the inner periphery 12d for the center of the outer periphery 12D of the annular wall 12, and the chucking mistake of the spindle shaft tip part 18 mounting on the annular wall 12 can be eliminated.
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