Interferometry using laser holography is applied for the purpose of measuring gear tooth flank form deviation of involute helical gear. The accuracy of the measurement by this method is comparable with that of the conventional measuring method using a contacting stylus. One problem with this method is that the curved tooth according to the helix angle of a helical gear interferes with the region of the flank to which the laser beam can be irradiated. The main reason for this interference is not due only to the existence of neighbouring tooth flank, but also to the fact that the incidence side of the objective tooth flank itself intercepts the beam irradiation upon the flank. To solve this problem, a method is proposed: As the first step, the objective tooth flank to be measured is divided into separate regions, and the contact free measuring is worked out. The measured values for the form deviation of tooth flank in each region are then concatenated into one on the whole plane of action, which results in a curved surface for the form deviation of the whole tooth flank of a helical gear.
