| 摘要 |
PROBLEM TO BE SOLVED: To provide a twist drill that shows stable performance by virtue of an improved chip evacuating flute leading to prevention of cutting edge chipping by chip jamming while chips are evacuated and to promotion of coolant penetration into the chip evacuating flute. SOLUTION: The twist drill made of cemented carbide or of TiCN system cermet has in a sectional view taken perpendicularly to the axis thereof an S shape spreading from that portion of a chip evacuating flute which is just off the web thickness to a land side, and a salient at the heel of the chip evacuating flute. With a straight line drawn to contain the outside edge of the cutting edge and the drill axis, the distance between a perpendicular produced therefrom tangentially to the concave of the chip evacuating flute and a perpendicular produced therefrom tangentially to the salient of the heel is set above zero and not greater than 25% of the drill diameter.
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