| 主权项 |
1. A drill main body of an indexable drill disposed with a pair of first and second spiral flutes on a column-shaped outer circumferential surface with an inner blade tip cutting a hole center side mounted on a tip portion of the first spiral flute and an outer blade tip cutting a hole outer circumferential side mounted on a tip portion of the second spiral flute, the drill main body of an indexable drill discharging chips through the first spiral flute and the second spiral flute toward a shank while hole machining is performed with the inner blade tip and the outer blade tip,
the drill being a deep hole machining drill having a length L of the first spiral flute and the second spiral flute equal to or greater than 4D relative to a drill diameter D that is an outer diameter of the outer blade tip, the first spiral flute being formed with a constant flute bottom diameter, or with a flute bottom diameter having a positive gradient such that the flute bottom diameter increases toward the shank, in axial direction, and the second spiral flute being formed with a flute bottom diameter having a negative gradient such that the flute bottom diameter decreases toward the shank in axial direction. |
