PURPOSE: To reduce rotational torque of a cutter when drilling a hole and facilitate drilling by forming a cutter section by thin-wall cylindrical section, a knotched recessed section, a cutting edge whose whole bottom face is tapered, and an escape stepped section on an inner peripheral side of the cutting edge.
CONSTITUTION: After a clamp joint 30 is bonded on an outer peripheral face of a synthetic resin pipe 33, a tapping cutter 10 is inserted into a branch pipe 31. A male screw 15 of a feed screw section 11 is screwed in a female screw 32 of the branch pipe 31, and a cutter section 12 is advanced toward the pipe 33. Also, a handle 34 is rotated, and when a cutting edge 21 in the cutter section 12 comes into contact with the outer peripheral face of the pipe 33, a hole is drilled on a surface of the pipe 33 by the cutting edge 21 by taking advantage of rotation force and thrust of the feed screw section 11. At this time, since the whole bottom face of a cylindrical section 20 is the cutting edge 21 and there is a knotched recessed section 22 on the circumference, friction of the cutting edge 21 due to resin is reduced. Also, since friction due to the resin occurs only on the cutting edge 21 by an escape stepped section 23, it is possible to reduce rotation torque of the handle 34.
KATO TAKESHI
NISHIKATA NOBUHIRO
HITACHI METALS LTD