| 摘要 |
A drill capable of efficiently performing high-quality drilling machining on a material which is hard to be cut such as CFRP and the like is provided. The drill includes a drill body 4 having a shank portion 2 at a rear side of the drill main body and a cutting portion 3 at a front side of the drill main body, a first land A to a fourth land D at the cutting portion 3, a first cutting portion groove 5a to a fourth cutting portion groove 5d provided between the lands of the first land A to the fourth land D, a pilot blade 6 formed at the tip of the cutting portion 3, a diameter-enlarging spiral thread portion 9 having a group of threads of diameter-enlarging spiral threads AK1-DK4 continuously following the pilot blade 6, a finished spiral thread portion 12 having a group of threads of finishing spiral threads AF1-DF5, which have the same height, and continuously following the diameter-enlarging spiral thread portion 9, a diameter-enlarging spiral blade portion 18 having a group of blades of the diameter-enlarging spiral threads AK1-DK4, and a finishing spiral blade portion 19 having a group of blade of the finishing spiral threads AF1-DF5. A cutting feed rate is set to an amount so that a spiral convex part will not be formed on the wall surface of a cutting hole formed in a material to be machined, and therefore the wall surface will be finished as a flat wall. |
