No, lapping does not change the basic tooth profile of a bevel gear. This is a common misconception. The tooth profile—meaning the theoretical shape of the tooth flank defined by the gear design parameters such as pressure angle, spiral angle, and depth—is established during the cutting process (e.g., by face milling or face hobbing). Lapping is a finishing operation that removes only a very small amount of material, typically on the order of a few microns, from the high spots on the tooth surface. It does not alter the macro-geometry of the tooth, such as the involute curve or the lead crowning.
The primary purpose of lapping is to improve two specific characteristics: surface finish and contact pattern. During lapping, the abrasive paste wears down microscopic peaks left by the cutting tool, resulting in a smoother surface with lower friction. At the same time, running the gear against its mating gear under controlled load allows the contact pattern—the area where the two teeth actually touch—to become more uniform and centered. This reduces localized stress and noise. However, if a bevel gear has large errors in tooth profile, lead angle, or tooth spacing (e.g., due to a dull cutter or incorrect machine setup), lapping will not correct these issues. In fact, lapping might mask them temporarily, but under load, problems like edge contact, uneven load distribution, or early pitting will still occur. Therefore, lapping should never be used as a repair process. The gear must be cut to a reasonable quality level (e.g., DIN 7 or better) before lapping. Lapping is the final step in a quality production line, not a substitute for proper cutting or grinding.