PURPOSE: To provide a lapping finish method which performs lapping and reduces production of a machining error.
CONSTITUTION: A eccentric pinion is rotated at a constant speed and a gear connected to a brake device is engaged therewith under the presence of a lapping agent to perform lapping of two tooth surfaces. A fluctuation in rotation torque in a reverse direction to that of a conventional one wherein brake torque TB is constant is produced at a gear in a way that, based on the accumulation error of the pinion or the gear, the more the rotation angle acceleration is increased, the more the brake torque TB of a brake device is decreased. At a part wherein the accumulation pitch error of a pinion 10 is high, rotation torque TG of a gear is increased and a lap amount is increased. Meanwhile, at a part wherein the accumulation pitch error is low, a lapping amount is decreased and the accumulation pitch error is decreased.