To prevent the penetration of a coolant by supplying a pressurized gas into a cap in order to make the cap internal pressure higher than the external pressure of the cap.
The grinding wheel spindle 2 of a wheel spindle stock 15 is rotated to rotate a grinding wheel 1, whereby a work W is polished. At this time, a coolant is injected toward the grinding wheel 1 and the work W. A cap 9 mounted on a wheel cover 21 has only one injection port 8 for injecting a fluid to a pocket 5, and a pressurized gas is supplied into the cap 9 through a pressured gas supplying port 13. The internal pressure of the cap 9 is kept higher than the external pressure of the cap 9. Therefore, the coolant is never penetrated into the pocket 5 of a wheel ring 4 arranged with an opening part 6 being turned in the axial direction of the grinding wheel spindle 2 in the front of the grinding wheel 1.
HASHIMOTO KATSUHIRO
YANAGIHARA SHIGERU
