| 摘要 |
Provided is a three-bladed drill that obtains, without decreasing drill rigidity, a sufficient supply of cutting fluid through a cutting fluid supply hole even without increasing the cutting fluid supply pressure. A cutting fluid supply hole (22) that is provided in a groove (16) has a fan shape cross-section enclosed by: a front inner wall face (FH) that is located in the radial direction on the side in the forward direction of rotation (RT) of a three-bladed drill (10); a back inner wall face (RH) that faces, in the circumferential direction, the front inner wall face (FH) and that is located in the radial direction on the side in the reverse direction of rotation (RT) of the three-bladed drill (10); an outer circumferential inner wall face (OH) comprising a partial face of a cylinder centered around the center line (C) of the three-bladed drill (10); and an inner circumferential inner wall face (IH) that faces, in the radial direction, the outer circumferential inner wall face (OH), and that comprises a partial face of a cylinder centered around the center line (C) of the three-bladed drill (10) with a radius of curvature (R2) that is smaller than the radius of curvature (R1) of the cylinder for the outer circumferential inner wall face (OH). Therefore, the core diameter can be ensured and the speed of the cutting fluid in the cutting fluid supply hole (22) can be increased even when the supply pressure of the cutting fluid is not increased, thereby increasing the supply of the cutting fluid. |
