scope:

This standard establishes a classification system, which can be used to communicate geometrical accuracy specifications of unassembled bevel gears, hypoid gears, and gear pairs. It defines gear tooth accuracy terms and specifies the structure of the gear accuracy grade system and allowable values.

This standard provides the gear manufacturer and the gear buyer with a mutually advantageous reference for uniform tolerances. Ten accuracy grades are defined, numbered 2 to 11, in order of decreasing precision. Equations for tolerances and their ranges of validity are provided in 5.4 for the defined accuracy of gearing. In general, these tolerances cover the following ranges:

1.0 mm ≤ mmn ≤ 50 mm

5 ≤ z ≤ 400

5 mm≤ dT ≤ 2500 mm

where

dT is tolerance diameter;

m_mn is mean normal module;

z is number of teeth.

See clause 6 for required and optional measuring methods. As tolerances are calculated from the actual dimensions of a bevel gear, tolerance tables are not provided. In order to get an overview, example values of tolerances and graphs are given in annex A.

This standard does not apply to enclosed gear unit assemblies, including speed reducers or increasers, gear motors, shaft mounted reducers, high speed units, or other enclosed gear units which are manufactured for a given power, speed, ratio or application.

Gear design is beyond the scope of this Standard. The use of the accuracy grades for the determination of gear performance requires extensive experience with specific applications. Therefore, the users of this standard are cautioned against the direct application of tolerance values to a projected performance of unassembled (loose) gears when they are assembled.

Tolerance values for gears outside the limits stated in this standard will need to be established by determining the specific application requirements. This could require the setting of a tolerance other than calculated by the formulas in this standard.