BACKING PLATE FOR RACEWAY SURFACE MACHINING OF INNER AND OUTER RINGS OF BEARING

PROBLEM TO BE SOLVED: To enhance machining accuracy by increasing a frictional force between a workpiece supporting surface of a backing plate for transmitting a rotation of a workpiece and the workpiece, and use a diamond sintered body and a cubic boron nitride sintered body as material of the backing plate in inner and outer rings having small diameter, of a bearing, in a raceway surface machining of the inner and outer rings of the bearing. SOLUTION: The workpiece supporting surface of the backing plate 1 in a raceway machining device of the inner and outer rings of the bearing is formed of the diamond sintered body 10 or the cubic boron nitride sintered body, and the surface roughness of the workpiece supporting surface is 0.08 to 0.20 μm. A plurality of grooves 10a are formed in which an opening width of a surface is 0.05 to 0.50 mm and an accumulated opening area is within a range from 30 to 70% of a contact area with respect to the workpiece. The grooves cross each other so that a cross angle is within a range from 60 to 90 degrees inside the workpiece supporting surface. Accordingly, the frictional force between the supporting surface and the workpiece is enhanced to restrain slip of the workpiece and reduce a loss in rotation, thereby realizing the high machine accuracy.