Sumitomo Electric Industries, Limited

Yoshio Dohi

Yoshikatsu Mori

Hideo Fukagawa

A drill made of cemented carbide, is constructed for compensating for the brittleness of cemented carbide to increase its cross-break strength. For this purpose, the ratio of the diameter c of the web portion (1) to the drill diameter d is set in the range of 25% to 35%, and the flute width ratio (b:a) is set in the range of 0.4:1 to 0.8:1. Further, to decrease the cutting resistance on the drill, the radial rake .theta..sub.r angle of the cutting lip 4 measured at positions spaced at least 2/3 of the drill diameter toward the outer peripheral side is set in the range of -5.degree. to positive valves. Furthermore, to promote the chip ejecting function, the relative distance L between the cutting lip 4 and the flute wall 5 opposed thereto, is decreased.

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Itami, Japan

Yoshio Dohi