PURPOSE: To prevent an exfoliation between rotary power transmitting substance and pad main unit, by uniformly constructing the rotary power transmitting substance and the pad main unit in a manner of embedding state.

CONSTITUTION: A rotary power transmitting substance 1 comprises a metallic plate unit 2 and a screw unit 3, vertically provided in its center portion by way of weldings, and of such constitution with a penetration hole 4 provided in the metallic plate unit 2 and the screw unit 3 made connectable to a drive shaft of the grinder main unit. On the other hand, the metal mold comprises a lower metal mold 5 and an upper metal mold 6, and in the lower metal mold 5 is constructed a recessed portion 7 of the same shape as that of the pad, simultaneously in its center part is constructed a screw unit engaging and holding recessed part 8 for engaging and holding the screw unit 3 of the rotary power transmitting substance 1. And after a positioning of the rotary power transmitting substance 1 in the metal mold 5, 6, a forming material is poured from a filling hole 9 and filled into the recessed portion 7.