| 摘要 |
Provided is a drill such that a sufficient amount of cutting liquid fed through a cutting liquid feeding hole is ensured without lowering the rigidity of the drill and without increasing the cutting liquid feeding pressure. The cutting liquid feeding hole (22), which is formed within a fluted portion (16), has a fan-shaped cross section which is enclosed by: a forward-side inner wall (FH) located forward relative to the direction of rotation (RT) of the drill (10) and along a radial direction thereof; a rearward-side inner wall (RH) located rearward relative to the direction of rotation (RT) of the drill (10) and along a radial direction thereof and facing the forward-side inner wall (FH) in a circumferential direction; an outer-circumference-side inner wall (OH) which is formed from a partial cylindrical surface centered on the central line (C) of the drill (10); and an inner-circumference-side inner wall (IH) which is formed from a partial cylindrical surface which is centered on the central line (C) of the drill (10) and has a curvature radius (R2) smaller than the curvature radius (R1) of the outer-circumference-side inner wall (OH), said inner-circumference-side inner wall (IH) facing the outer-circumference-side inner wall (OH) in a radial direction. Since the cutting liquid feeding hole (22) has the abovementioned fan-shaped cross section, sufficient web thickness can be ensured while the speed of the cutting liquid inside the cutting liquid feeding hole (22) can be increased without having to increase the cutting liquid feeding pressure, thereby increasing the amount of cutting liquid fed. |
