| 摘要 |
<p>A small drill having a high rigidity, an excellent chip dischargeability, and a high hole centering accuracy, wherein a chip discharge groove (12) and a groove-shaped part (15) allowed to communicate with the chip discharge groove (12) on the drill rotating direction (T) forward side and opening to the peripheral surface of a blade tip part (11) are provided in the peripheral surface of the blade tip part (11), the ratio of a core thickness (d/D) is set at 60% or higher, and a margin angle (υ) is set at 120°or more.</p> |
