| 摘要 |
PROBLEM TO BE SOLVED: To maintain pre-load of a rear bearing even if a main spindle is thermally expanded to displace the position in the axial direction of the rear bearing by inserting the rear bearing in an outer cylinder under the condition in which pre-load is given between the inner/outer rings and the rolling bodies. SOLUTION: By properly correcting and adjusting the thickness of a collar 5b relative to the thickness of a collar 5a, appropriate pre-load is given to a bearing, and because a main spindle is rotatably journaled in a housing, the position in the axial direction of the front part of the main spindle is fixed. When the main spindle is thermally expanded, the rear part, i.e., the outer cylinder of the rear bearing is exclusively displaced in the axial direction together with the rear bearing and the main spindle. At this time, a rear bearing 7 is fitted to the main spindle in the pressed condition by a rear bearing inner ring pressing nut 17 threadedly engaged with the screw part 9d formed on the rear end part of the main spindle through a collar, similarly a collar 7b is inserted between the outer rings of the rear bearing 7 to be fitted to an outer cylinder 19, and hence pre-load is maintained.
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