| 摘要 |
PROBLEM TO BE SOLVED: To prevent chipping by improving cutting edge strength of an outer circumferential side part without impairing cutting quality of a tool center side part. SOLUTION: A chamfer 22 is set at a rake face side 20 of a ball blade 18 constituted of a CBN tip 16, and the width dimension A of the chafer 22 is made to be gradually increased towards the outer circumferential side from the tool center side. As a result, the width dimension A of the chamfer 22 is small at the tool center side part, and the excellent cutting quality is obtained even at a low surface speed, on the other hand, at the outer peripheral side part, the width dimension A of the chamfer 22 is large, the cutting edge strength is improved, and an excellent durability is obtained since the chipping is restrained even at a high surface speed and with large cutting resistance.
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