| 摘要 |
PROBLEM TO BE SOLVED: To improve the service life of a tool by suppressing breakage and chipping by the blocking and biting of chips in a spiral tap for discharging chips to the shank side. SOLUTION: A groove portion 20a located in a complete ridge part 16 out of a groove 20 provided in a threaded portion 12 is a straight groove of the spiral angle of 0 deg., i.e., parallel to the axis, and the width of the groove is large. A groove portion 20b located in a biting part 18 is parallel to the axis similar to the complete ridge part 16 in an opening edge on a heel 24 side opposite to a cutting blade 22 while the spiral angle of the opening edge on the cutting blade 22 side is in a range of 30-45 deg. (about 40 deg. in the embodiment), and the opening edge is twisted clockwise similar to the spiral direction of the thread of the threaded portion 12, and becomes narrower toward the tip of the tool.
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