| 摘要 |
A drill (10, Fig 1A) including a shank portion (14, Fig 1A) and a cylindrical body portion (16, Fig 1A) contiguous to each other. The cylindrical body portion (16, Fig 1A) includes (a) primary cutting edges 12 and secondary cutting edges 46 formed in its axially distal end portion such that each of the secondary cutting edges 46 is located on a radially inner side of the corresponding primary cutting edge 12 ; (b) primary rake surfaces 13 of the primary cutting edges 12 and secondary rake surfaces 48 of the secondary cutting edges 46 ; and (c) inclined surfaces 52 each of which extends from the corresponding secondary rake surface 48 to a periphery of the cylindrical body portion, and is inclined such that an axial distance between each of the inclined surfaces 52 and the shank portion 16 is reduced as viewed in a direction substantially perpendicular to the corresponding secondary cutting edge 46 , from the corresponding secondary rake surface 48 toward the periphery of the cylindrical body portion 16 . Each of the secondary rake surfaces 48 and the corresponding secondary cutting edge 46 are formed together with each other in a web thinning. Each of the secondary rake surfaces 48 and the corresponding inclined surface 52 are connected to each other without a step therebetween. The drill also has flutes 18 and margins 20. |
