TAP FOR THREADING DEAD OPENINGS Russian patent published in 2002 - IPC

FIELD: metal working. SUBSTANCE: tap includes stem and feathers with sizing portion passing to take-off portion having leading and back surfaces and beveled cut whose bevel value is selected according to thickness of cut, length of take-off portion and back angle of said portion. In order to enhance versatility and useful life period of tap due to reduced unscrewing torque and to decrease number of rejected parts due to elimination of loosening of thread size, beveled cut is arranged at side of rear edge of feather; angle and length of beveled cut are selected according to given formulae. Beveled cuts may be provided on all feathers except first one. EFFECT: enhanced versatility, increased useful life period of tap. 2 cl, 5 dwg