Method of grinding core blank for magnetic heads, using markers for determining grinding depth for nominal magnetic gap depth

A method of grinding a core blank which yields at least one head core each used for a magnetic head, each of said at least one head core having an annular magnetic path having a magnetic gap, said core blank having a working surface which is ground to thereby give a sliding surface of said each head core that is opposed to a magnetic recording medium for sliding contact therewith, said method comprising the steps of:

• forming at least one first marker and at least one second marker by photolithography so that said markers are embedded in said core blank, each of said at least one first marker consisting of two straight segments each having a predetermined width, said two straight segments meeting each other to form a V-shape on a grinding depth line, which determines a nominal depth dimension of said magnetic gap, and having respective edges defined by said two straight segments, each of said at least one second marker consisting of a first right-angled isosceles triangle, and a second right-angled isosceles triangle which is obtained by rotating said first right-angled isosceles triangle by 90.degree. about an apex thereof, said first and second right-angled isosceles triangles having respective bases as edges of said second marker, said edges of said markers being spaced from each other in a direction of width of said magnetic gap by a first distance that continuously varies in a direction of depth of said magnetic gap, said edges of said markers being located on the same side as viewed in the direction of width of said magnetic gap;
• and
• measuring, upon grinding of said core blank, said first distance between said edges of said markers which is exposed on said working surface of said core blank under grinding, which first distance varies with a second distance between said working surface under grinding and said grinding depth line, so as to determine a required residual depth of grinding which is to be further effected to establish the nominal depth dimension of the magnetic gap;
• wherein said first and second triangles of said at least one second marker are positioned such that said grinding depth line crosses said respective bases and said first distance between said respective edges of said markers continuously increases with an increase in said second distance between said working surface and said grinding depth line.