This invention solves the difficult problem that the common normal line of involute internal helical gear cannot be measured previously. This measuring method and device not only has such advantages of convenience in operation, simple construction, and easy make, but also its high measuring precision, even higher than that obtained by a dial gauge if the measuring head of a pneumatic gauging device is used as the measuring head of the "T" shape device. This can not be achieved by the measuring of the common normal line on external gear. Meanwhile, the measuring of the common normal line of internal helical gear indicated by this invention is not restricted by the thickness of the gear tooth. (except for certain specific light duty gears having very narrow gear width.) |