| 摘要 |
PROBLEM TO BE SOLVED: To provide a twist drill which can drill a deep hole of a depth 20 to 40 times drill diameter at a stroke. SOLUTION: The twist drill for deep hole is provided with a first web and a second web whose web thicknesses are constant from the top side toward the base side. The web thickness of the first web is thicker than that of the second web, and the curvatures of the drill flute bottom differ between the top side and the base side. Besides the web thickness of the first web is thinner than the drill diameter by 2 to 8% and the web length of the first web is 1/2 to 10 times the drill diameter, for improved chip discharge.
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