| 主权项 |
1. A rotary drill bit for engaging an earth strata material, the rotary drill bit comprising:
an elongate drill bit body having an axial forward end and an axial rearward end; and a cutting insert attached to the axial forward end of the elongate drill bit body, the cutting insert having an elongate insert body rotatable about a central axis, the elongate insert body having a pair of symmetrical halves symmetrical about the central axis, each symmetrical half comprising:
a leading face;a top surface having a primary relief surface;a web thinning gash extending between the leading face and the primary relief surface of the top surface, the web thinning gash having a debris evacuation portion centrally disposed adjacent the central axis and a distal transition portion disposed adjacent the debris evacuation portion;a first leading cutting edge at the intersection of the leading face and the primary relief surface of the top surface; anda second leading cutting edge at the intersection of the web thinning gash and the primary relief surface of the top surface, the second leading cutting edge being continuous with the first leading cutting edge, wherein the web thinning gash defines a negative rake angle at the second leading cutting edge. |
