PURPOSE: To make some flutes in a ferrite magnetic material or a composite material containing this magnetic material (for a magnetic head material) by a method wherein a grinder stone including a layer having rough degree of granules form at a central part in its thickness direction and other layers at both ends of the central layer with more fine degree of granules than that of the central part.

CONSTITUTION: In case that a ferrite magnetic material is fluted up to a depth of about 2mm, diamond grinder granules having an average granule diameter of about 15μm are applied to a rough layer 1 of granules, other diamond grinder granules having an average granule diameter of about 8μm are applied to the fine layer 2 of granular degree. A thickness of fine granular diameter layer t is made such that a maximum chipping of 10μm in the surface and an accuracy of working surface of 3μm/2mm may be provided when a metal bond grinder stone of about 20μm is operated under a rotational speed of 60mm/min. In this type of flutes cutting it is possible to keep tipping or cut low in the working surface, and improve a working efficiency together with superior accuracy in surfaces.