| 摘要 |
PURPOSE: A cutting property and a chip discharging property are improved by changing angle of the chip discharging groove. CONSTITUTION: A drill comprises a front end forming a cutting edge, a chip discharging groove of a spiral shape, and a spiral land forming a borderline with the chip discharging groove. The drill body is divided from the front end to the other end into a first length portion, a transitional portion, and a second length portion. The chip discharging groove has a first angle in the first length portion. The chip discharging groove in the transitional portion is formed to be changed to a second angle smaller than the first angle. The chip discharging groove has the second angle in the second length portion. The second angle is about 60-85 percent of the first angle.
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