PURPOSE: To crush hard scales on a metallic plate and to increase the efficiency of a grinding work by knocking the surface of the metallic plate with a metallic cylindrical heavy hone held with an elastic wire.

CONSTITUTION: A cylindrical shaped grinding hone 5 of a 20W10gr weight is made by solidifying grinding materials such as carborundum, alundum and, etc. with a metallic powder binder. The hone 5 is supported by a wire 4 which comprises a core made of a bundle of a numbers of elastic synthetic fiber strings and a sheath made of synthetic fiber braids around the core and bonded with a resin paste. At the lower end of the hone 5 a plastic base cylinder 6 is fixed, and futher on the periphery of a disc 2 a plurality of plastic attaching plates 3 are fixed end-to-end, and then the upper end of the wire 4 is fixed to the base cylinder 6, and similarly the lower end thereof is inserted into and fixed to the attaching plates 3. Consequently, the hone is knocked strongly on the metallic plate like a hammer while a roll brush is rotated, and scales are easily descaled.