A head chip having a track width of a gap smaller than a thickness of a core enables a high density recording of a video signal. The track width of the gap is machined before a bulk is sliced into individual head chips to save manufacturing time and enhance yield. An efficient machining of the track width is achieved using a plurality of hard metal wires such as piano wires spanned on rollers each having a plurality of precisely spaced grooves thereon and reciprocating the metal wires while dropping grinding liquid thereon. In this manner, the occurrence of chipping of core material is minimized or the size of chipping, if any, is minimized.