The formulae are intended to establish uniformly acceptable methods for calculating the pitting resistance and bending strength of straight, helical (skew), spiral bevel, Zerol and hypoid gears. They are applicable equally to tapered depth and uniform depth teeth. The term bevel gear refers to all of these gear types; if not the case, the specific forms are identified.
The formulae take into account the known major factors influencing pitting on the tooth flank and fractures in the tooth root. The rating formulae are not applicable to other types of gear tooth deterioration such as plastic yielding, micropitting, case crushing, welding, and wear. The bending strength formulae are applicable to fractures at the tooth fillet, but not to those on the active flank surfaces, to failures of the gear rim or of the gear blank through the web and hub. Pitting resistance and bending strength rating systems for a particular type of bevel gears can be established by selecting proper values for the factors used in the general formulae. If necessary, the formulae allow for the inclusion of new factors at a later date. The rating system of ISO 10300 (all parts) is based on virtual cylindrical gears and restricted to bevel gears whose virtual cylindrical gears have transverse contact ratios of εvα < 2. Additionally, the given relations are valid for bevel gears of which the sum of profile shift coefficients of pinion and wheel is zero (see ISO 23509).