DRILL

PROBLEM TO BE SOLVED: To provide a drill capable of reducing a load applied to the drill when a cast hole is cut for example, and keeping a long service life of a tool, and in addition capable of improving working accuracy. SOLUTION: The drill 10 includes a blade 12 having spiral cutting edges 16 and 18 formed to extend along a cutting direction from a tip to a tail, and a shank 14 formed continuously with the tail of the blade 12. The blade 12 has tip cutting edges 16a and 18a formed along the cutting direction from the tip of the blade 12 by a certain helix angle α1, intermediate grooves 16b and 18b formed by a helix angle αx gradually varying from the first helix angle α1 to a second helix angle α2, and a tail grooves 16c and 18c formed by the certain helix angle α2. The tail grooves 16c and 18c are specified to be longer in lengths in the cutting direction than those of the tip cutting edges 16a and 18a, and in addition, the second helix angle α2 is specified to be smaller than the first helix angle α1. COPYRIGHT: (C)2009,JPO&INPIT