Patent ID: 9623490
Date: 2017-04-18
CPC Classifications: B23B,Y10T

Claim:
1. A three-flute drill comprising: a tool main body provided with cutting edges at an axially distal end of the tool main boy, a flute portion having discharge flutes formed in a distal-end side portion of the tool main body for discharging chips generated by the cutting edges, and a cutting fluid supply hole for supplying cutting fluid toward the cutting edges through an inside of the flute portion, the cutting fluid supply hole having a tan-shaped cross section defined by a front inner wall surface extending along a radial direction of the three-flute drill on a front side in a rotation direction of the three-flute drill, a rear inner wall surface extending along the radial direction on a rear side in the rotation direction of the three-flute drill and opposed to the front inner wall surface in a circumferential direction of the three-flute drill, an outer circumferential inner wall surface made up of a partially cylindrical surface whose center lies on an axis of the three-flute drill, and an inner circumferential inner wall surface made up of a partially cylindrical surface whose center lies on the axis of the three-flute drill and opposed to the outer circumferential inner wall surface in the radial direction, the inner circumferential inner wall having a curvature radius smaller than a curvature radius of the outer circumferential inner wall surface.