Kabushiki Kaisha Fujikoshi

Yutaka Yoshida

Tadao Ishikawa

Toshiyuki Sunakoda

A drill for use in drilling hard and brittle materials includes a shank and a drilling portion attached to one end of the shank. The drilling portion includes a tapered primary cutting edge, a first secondary cutting surface extending from the primary cutting edge and having an angle of taper substantially identical to that of the primary cutting edge, and a second secondary cutting surface extending from the first secondary cutting surface and containing a line substantially parallel to the central axis of the drill. The primary cutting edge has a first abrasive grain layer, and the first and second secondary cutting surfaces both have a second abrasive grain layer. The first and second abrasive grain layers both have a binder made of material selected from the group consisting of metal, resin and glass. Each abrasive grain in the first abrasive grain layer has a diameter greater than that of each abrasive grain in the second abrasive grain layer.

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Himi, Japan

Yutaka Yoshida