PURPOSE: To prevent the eccentric fitting of a grinding wheel to a bracket to improve grinding accuracy of a workpiece.

CONSTITUTION: Through holes 11, into which bolts threadely engaged with a bracket integrated with a motor rotation shaft can be inserted without play, are drilled first in a base metal 8, and then the outer-diameter dimension, a fitting hole 12, and a grinding part 8a of the based metal are worked in prescribed dimensions with the through holes 11 as reference. This causes the inevitable conformity of both center lines of the bracket and a grinding wheel 9 when the grinding wheel 9 after manufacturing is fixed to the bracket, thereby eliminating deflection of a centerline during rotation.