| 摘要 |
PROBLEM TO BE SOLVED: To shorten the machining time for forming an arc-shaped groove in a cylindrical article by extending a ring-like holding zone having an individual projection from the bottom of a tool body and holding an inversion cut chip for deciding the side face profile of the groove in the inner side of each projection. SOLUTION: A hanging bell type counterbore 11 for forming a groove used for holding and fixing a turbine blade is provided with a sunbstrantially crown- like tool body 12. In this tool body 12, an edge formed as a holder zone 14 is extended from its bottom 13 in an axial direction. In the holder zone 14, notches 15 (15a to 15c...) are formed at intervals in a peripheral direction so as to be opened away from the bottom 13 in a radial direction inner side, an outer side and an axial direction and projections 16 (16a to 16c...) are formed between the notches 15. The outer side of each projection 16 is firomed to be step-like and its inner side is formed corresponding to the side face profile of the groove. An inversion cut chip 21 is held in a chip seat 19 formed inside the projection 16. |
