| 摘要 |
PROBLEM TO BE SOLVED: To provide a stable twist drill of cemented carbide or of TiCN system cermet that excellently resists cutting edge chipping, coating flaking and the like by virtue of an improved end cutting edge and 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. The chip evacuating flute has a concave root and a convex heel. In the end face view of the twist drill, an end cutting edge is formed straight and is connected to a web thinning edge by an arc 0.15 to 0.50 times as long as the drill diameter.
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