Patent ID: 9522428
Filing Date: 2016-12-20
CPC Classification: B23B,Y10T

Claim Text:
1. A small-diameter drill having a diameter of φ3 mm or less and an end that has undergone cross thinning, wherein in a front view, a flute portion cutting edge is curved in concave against a rotational direction with respect to an imaginary straight line that connects a radially outer end of the flute portion cutting edge and a radially outer end of a thinning portion cutting edge, a degree of concavity of the flute portion cutting edge with respect to the imaginary straight line is set in a range of 0.5 to 2% of a drill diameter, furthermore, a ratio B:A of a length B of the thinning portion cutting edge to a length A of the flute portion cutting edge is set to 0.6 to 0.9:1, and in an axially perpendicular cross-sectional view, a curvature radius R