| 摘要 |
PURPOSE: To provide a drill improved in the chip discharging performance by cutting liquid running in a flute without loosing the rigidity to improve the cutting performance. CONSTITUTION: A plurality of flutes 22 are formed on a shaft 12 in such a manner that the section of the flute 22 gradually increases from the chip end having a cutting edge of the drill shank 12 toward an intermediate part 20 and the twist angleαgradually reduces in the same manner. |
