| 摘要 |
PROBLEM TO BE SOLVED: To improve punching speed by preventing punching powder from falling in inter-chip spaces through a discharge groove, to suppress vibration at the time of a punching and to improve roundness of a hole formed by the punching. SOLUTION: In a drill head 22 to form a distal end of a drill bit 2, the four inter-chip spaces 22a to 22d are formed. The two spaces 22a and 22b of the spaces 22a to 22d are communicated with a spiral groove 21a via the discharge grooves 22e and 22f. At a connecting position 21e except a position closest to a distal end of the drill head 22 of connecting positions 21d and 21e to the spiral groove 21a of the discharge grooves 22e and 22f communicated with the spiral groove 21a, a projecting part 22A is provided. The discharge groove 22e is covered with a lid at the connecting position 21e. COPYRIGHT: (C)2005,JPO&NCIPI
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