| 摘要 |
PROBLEM TO BE SOLVED: To provide a pre-load variable spindle unit which can smoothly switch bearing pre-load application irrespective of operating conditions. SOLUTION: According to the structure of the pre-load variable spindle unit, an axial dimension of a spiral groove 2a formed in a sliding surface of an external cylinder 2 with respect to a bearing box 7, is set to 1.5 to 2.0 times the axial dimension of a spiral land portion 2b defined between the spiral grooves 2a. By virtue of this setting, a suitable gap is formed between the bearing box 7 and the external cylinder 2 by pressure oil filled in the spiral groove 2a. Further, under the operating conditions in which the temperature of a rotary system including bearings 3, 4 is likely to increase, heat generated in the rotary system is sufficiently discharged via the land portion 2b to a static system including the external cylinder 2, to thereby prevent narrowing of the gap between the bearing box 7 and the external cylinder 2. When the bearing pre-load application is switched, axial movement of the bearing box 7 is always smoothly carried out, and therefore defective switching operation rarely occurs. COPYRIGHT: (C)2006,JPO&NCIPI
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