Patent ID: 6315504
Filing Date: 2001-11-13
Classification: B23B,Y10T

Abstract:
A twist drill comprising:a drill body rotatable about an axis in a drill rotation direction and having an outer peripheral surface and a tip end;a pair of chip discharge flutes formed in the outer peripheral surface of said drill body;a pair of chisel edges formed on the tip end of said drill body, each of the pair of chisel edges having an outer end;a pair of inner cutting edges extending from each outer end of said chisel edges, each of the pair of inner cutting edges having an outer end;a pair of major cutting edges extending from each outer end of said inner cutting edges;a pair of outer cutting edges each receding relative to the drill rotation midway back from each of said major cutting edges at a first angle (.alpha.1) in a counter-direction of the drill rotation; anda pair of leading edges of lands each formed by a land and said outer cutting edge, each said leading edge having a linear or curved rake face;wherein a second angle (.alpha.4) of each said leading edge of the lands between the land and the linear or curved rake face of each said leading edge is an obtuse angle.