With a given transmission design, the machining accuracy of the gear is responsible for the frequent differences in noise. In general, the frequencies of the tooth contacts under load determine the noise. Gear errors and the assembly conditions cause highly different noise excitations that may be as well amplified by resonance as reduced by damping.
The influence of the errors of helical angles and pressure angles, of axial and radial crowning, and of tooth spacing errors on gear noise are described, and manufacturing methods are explained which, with a manufacture based on tooth shaving, limit the said errors to such a degree that, as to noise, shaved gears are equivalent or even superior to ground ones. In particular, the dimensional changes during the hardening process are analyzed, as the distortions due to hardening must already be considered during the shaving process.