| 摘要 |
PROBLEM TO BE SOLVED: To provide a drill which can avoid trouble due to chips by facilitating discharge of chips from a machined hole, and prevent breakage of the drill due to insufficient rigidity or deterioration of dimension accuracy of the machined hole by ensuring the rigidity of the drill body. SOLUTION: In the drill, a chip discharge groove 20 which is twisted around the axis O and extends toward the rear end side is formed on the outer periphery of a cutting blade part 12 formed at the tip end side of the drill body 10 rotated around the axis O, and a cutting blade 30 is formed at the intersection edge line part of the inner wall surface facing the front side of the drill rotation direction of the chip discharge groove 20 and the tip end flank 13 of the cutting blade part 12. The cutting blade part 12 is provided with a groove expansion part 16 which is formed so that the cross section area on the section orthogonal to the direction of the axis O of the chip discharge groove 20 gradually becomes large as it advances toward the rear end side of the cutting blade part 12, and the helix angleαof the chip discharge groove 20 gradually becomes small as it advances toward the rear end side of the cutting blade part 12. COPYRIGHT: (C)2007,JPO&INPIT
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