TWIST DRILL

PROBLEM TO BE SOLVED: To improve both durability of a drill and stability of cutting performance by reducing cutting resistance (thrust load), while suppressing crater wear of a rake face of a cutting edge of a thinning part of the drill having a narrower width of a chisel edge between right and left cutting edges by performing thinning processing. SOLUTION: In this drill, drill radial direction inner ends 6a of right and left thinning grooves 6 are arranged at positions beyond a drill center O, and the inner ends 6a sides of the thinning grooves 6 are partially overlapped in a range of δ in the drill radial direction. A rake angle of the cutting edge 3a of the thinning part formed between each thinning groove and a flank 7 at a distal end of the drill is set to be a negative angle. COPYRIGHT: (C)2008,JPO&INPIT