To provide a drilling tool with excellent practicality and considerably improved chip discharge performance and fracture resistance than conventional under cut type drills.
The under cut type drilling tool includes a body section 2 with a blade section 1, and a shank section 3. One or plural helical chip discharge grooves 4 extending from the distal end of the tool toward the basal end thereof are formed in the outer periphery of the blade section 1. The diameter of the basal end side of the body section 2, except for the distal end of the blade section 1, is decreased by one step. Between the chip discharge grooves 4 and a land section 5, a shoulder 6 for forming a clearance is one step lower than the land section 5 is disposed from the distal end of the blade section 1 in the range of 40% or more of the length of the body section 2.
TORIGOE KATSUAKI
TSUSAKA HIDEO
| JP2006043875A | 2006-02-16 |
Masae Yoshii
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