| 摘要 |
PROBLEM TO BE SOLVED: To provide a drill made of high speed steel or hard metal for deep hole where an improvement of scraps dischargeability and an improvement of rigidity are reconciled, the flow of scraps is not interfered with, further, a flexural rigidity and a torsional stiffness are enhanced. SOLUTION: In a drill for deep hole with helical flute which is made of high speed steel or hard metal, front edge core thickness part T1 which has 30-70% of length of an effective groove part of drill which deducted the length of an upvalued part of drill flute from the length of a drill groove and with the almost same web thickness is prepared, and at least one web taper part T2 along which web thickness becomes large smoothly and continuously and without level difference towards an upvalued part CS of the drill flute from the front edge core thickness part T1 is prepared.
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