| 摘要 |
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 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 DEG 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. |
