| 摘要 |
PROBLEM TO BE SOLVED: To reduce the size by uniting a tip for cutting a bearing surface and a tip for chamfering into one tip and to heighten the cutting efficiency by increasing the number of effective edges. SOLUTION: A pair of tips 4 serving as a tip for cutting a bearing surface and a tip for chamfering are disposed by shifting 180 deg. in phase. Two sets of edge parts 9 having a cutting edge 8a for cutting the bearing surface and a cutting edge 8b for chamfering are formed on the tip 4.
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