BS ISO 21771:2007

Foreword
1 Scope
2 Normative references
3 Symbols, subscripts and units
  3.1 Symbols
  3.2 Subscripts
  3.3 Units
4 Individual cylindrical gears
  4.1 Concepts for an individual gear
  4.2 Reference surfaces, datum lines and reference
      quantities
  4.3 Involute helicoids
  4.4 Angular pitch and pitches
  4.5 Diameters of gear teeth
  4.6 Gear tooth height
  4.7 Tooth thickness, space width
5 Cylindrical gear pairs
  5.1 Concepts for a gear pair
  5.2 Mating quantities
  5.3 Calculation of the sum of the profile shift
      coefficients
  5.4 Tooth engagement
  5.5 Backlash
  5.6 Sliding conditions at the tooth flanks
6 Tooth flank modifications
  6.1 Tooth flank modifications which restrict the usable
      flank
  6.2 Transverse profile modifications
  6.3 Flank line (helix) modifications
  6.4 Flank face modifications
  6.5 Descriptions of modifications by functions
7 Geometrical limits
  7.1 Counterpart rack tooth profile
  7.2 Machining allowance
  7.3 Deviations in tooth thickness
  7.4 Generating profile shift, generating profile shift
      coefficient
  7.5 Generated root diameter
  7.6 Usable area of the tooth flank, tip and root form
      diameter
  7.7 Undercut
  7.8 Overcut
  7.9 Minimum tooth thickness at the tip circle of a gear
Annex A (informative) Calculations related to tooth thickness
Bibliography

Defines the geometric concepts and parameters for cylindrical gears with involute helicoid tooth flanks. It also covers the concepts and parameters for cylindrical gear pairs with parallel axes and a constant gear ratio, which consist of cylindrical gears according to it.

This International Standard specifies the geometric concepts and parameters for cylindrical gears with involute helicoid tooth flanks. Flank modifications are included.

It also covers the concepts and parameters for cylindrical gear pairs with parallel axes and a constant gear ratio, which consist of cylindrical gears according to it. Gear and mating gear in these gear pairs have the same basic rack tooth profile.

The equations given are not restricted to the pressure angle, α_p=20°

The standard is structured as follows.

• Listing of symbols and nomenclature for a unique description of gears and gear pairs (see Clause3).

• Equations and explanations of the relevant values for defining a cylindrical gear and its tooth system. The equations for determination of the nominal values for zero-deviation gear description parameters are stated for radial tooth dimensions (gear tooth heights), the distance between flanks of the same hand, the distance between flanks of opposite hand, as well as the tooth flank characterizing parameters (see Clause4).

• Equations and explanations of the relevant values for defining cylindrical gear pairs. The equations for the essential parameters characterizing the engagement conditions of the unloaded gear pair are listed (see Clause5).

• Equations and suggestions for desired flank modifications (see Clause6).

• Concepts and recommendations needed for a unique geometrical definition of the intended results from manufacture (Clause7).

• Equations for determination of the nominal values or the limiting values for the most used inspection methods for tooth thickness (see AnnexA).