| 摘要 |
A twist drill (12) includes a cutting portion (10) and a drill body (14). The cutting portion (10) has a chisel edge (28), a segment relief surface (22), a chamfer relief surface (24) and at least two flutes (20) extending longitudinally to the drill body (14). Each flute (20) has a rake surface (34) and a gash (36) extending away from the chisel edge (28). The cutting portion (10) further has at least two cutting segments (18), each cutting (18) segment having a first curved cutting edge (38), a second curved cutting edge (40) and a chamfer cutting edge (42). |
