SCREW TAP Russian patent published in 2012 - IPC B23G5/06 

FIELD: process engineering.

SUBSTANCE: proposed screw tap has lengthwise axis and working part consisting of cutting and gauging parts, shank opposed to tap working end face. Cutting blades of cutting and gauging parts are made on wings separated by straight or screw flutes. Note here that cutting edges of blade teeth on every wing to cut thread root are located on intake cone the axis of which is aligned with lengthwise axis of screw tap and crest is located ahead of its working end face. Note also that every tooth of cutting part has two crests, i.e. near crest located along lengthwise axis and closer to working end face, and far crest located along lengthwise axis farther from working end face. Chamfer made parallel with tap lengthwise axis or at angle thereto is made on cutting part teeth farthest crest.

EFFECT: higher durability due to alignment of angles at far and near crests.

3 dwg