DIN ISO 21771:2014-08

This German standard is the translation of the first edition of the International Standard ISO 21771:2007 which has been prepared by Technical Committee ISO/TC 60 "Gears", Subcommittee SC 1 "Nomenclature and wormgearing". This standard specifies the geometric concepts and parameters for cylindrical gears with involute helicoid tooth flanks. Flank modifications are included. The standard 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 this standard. Gear and mating gear in these gear pairs have the same basic rack tooth profile. The equations given in this standard are not restricted to the pressure angle. The standard is structured as follows: - Clause 3: symbols and nomenclature for a unique description of gears and gear pairs. - Clause 4: Equations and explanations of the essential parameters 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. - Clause 5: Equations and explanations of the essential parameters for defining cylindrical gear pairs. The equations for the essential parameters characterizing the engagement conditions of the unloaded gear pair are listed. - Clause 6: Equations and suggestions for desired flank modifications. - Clause 7: Concepts and recommendations needed for a unique geometrical definition of the intended results from manufacture. - Annex A: Equations for determination of the nominal values or the limiting values for the most used inspection methods for tooth thickness. Application of the present informative Annex A cannot be recommended. The reason is the mixing of the "nominal tooth thickness system" (Germany) and the "functional tooth thickness system" (USA). This involves the risk of using wrong equations or quantities. Therefore, the informative Annex A of this standard cannot replace the normative content of DIN 3960. In order to solve this problem, those parts describing the "nominal tooth thickness system" have been transferred to a separate standard, DIN 21773. DIN ISO 21771 together with DIN 21772 and DIN 21773 replaces DIN 3960:1987. The national concerns during the preparation were represented by Working Committee NA 060-34-11 AA "Zylinderräder - Terminologie und Toleranzen (SpA ISO/TC 60/WG 2 und ISO/TC 60/SC 1/WG 4)" ("Cylindrical gears - Terminology and tolerances (national mirror committee for ISO/TC 60/WG 2 and ISO/TC 60/SC 1/WG 4)") at DIN Standards Committee Mechanical Engineering (NAM) in the department "Antriebstechnik" ("Drive technology") at DIN e. V., the German Institute for Standardisation. Previous editions: DIN 3960:1987-03; 1980-07; 1976-10.