| 摘要 |
PROBLEM TO BE SOLVED: To suppress heating of a bearing and prevent fusion of a housing by providing a spindle with a hollow part, providing many vent holes communicating with outside air on the one end side and communicating the other end side with a ventilation path into which outside air is flowed. SOLUTION: A spindle 3 has a hollow part 7. At one end side (chuck side) of the spindle 3, a plurality of vent holes 8 are provided at the outside of a housing 6, that is, at a location communicating with outside air and the other end side of the spindle 3 communicates with a ventilation path 9 provided at the housing 6. Because ribs between each adjacent vent hole 8 have the same action effects as that of a radial fan by revolution of the spindle 3, air within the hollow part 7 is exhausted to the outside from the vent holes 8. Outside air is taken into the hollow part 7 from the ventilation path 9. As a result, the spindle 3 is compulsorily cooled. As a result, heating of a bearing is suppressed and fusion of the housing 6 can be prevented.
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