ISO 22081:2021 pdf – Geometrical product specifications (GPS) — Geometrical tolerancing — General geometrical specifications and general size specifications.
1 Scope This document gives rules for definition and interpretation of general geometrical specifications and general size specifications defined according to ISO 8015:2011, 5.12. General specifications defined in other standards, and the link to these standards, are not covered by this document. The general geometrical specifications and general size (linear or angular) specifications defined in this document apply only to integral features (including features of size). These specifications do not apply to derived features or integral lines (see ISO 17450-1 for the definitions of integral features and derived features). Dimensions other than linear or angular sizes (see ISO 14405-2) are not covered by this document. 2 Normative references The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 8015, Geometrical product specifications (GPS) — Fundamentals — Concepts, principles and rules ISO 17450-1, Geometrical product specifications (GPS) — General concepts — Part 1: Model for geometrical specification and verification ISO 17450-2, Geometrical product specifications (GPS) — General concepts — Part 2: Basic tenets, specifications, operators, uncertainties and ambiguities ISO 22432, Geometrical product specifications (GPS) — Features utilized in specification and verification ISO 25378, Geometrical product specifications (GPS) — Characteristics and conditions — Definitions
3.2 general size specification size specification (linear size specification or angular size specification) indicated in the technical product documentation (TPD) which is not an individual specification Note 1 to entry: Linear size specifications are defined in ISO 14405-1. Angular size specifications are defined in ISO 14405-3. 3.3 integral feature geometrical feature belonging to the real surface of the workpiece or to a surface model Note 1 to entry: An integral feature is intrinsically defined, e.g. skin of the workpiece. Note 2 to entry: For the statement of specifications, features obtained from partition of the surface model or of real surface of workpiece shall be defined. These features, called “integral features ”, are models of the different physical parts of the workpiece that have specific functions, especially those in contact with the adjacent workpieces. Note 3 to entry: An integral feature can be identified, for example, by: a partition of the surface model; a partition of another integral feature; a collection of other integral features. [SOURCE: ISO 17450-1:2011, 3.3.5] 4 Basic principles 4.1 General When using general geometrical specifications or general size specifications, the designer should be aware of the following risks: — overlooking important functional requirements; — selecting unnecessarily tight tolerances regarding the functional requirement. It is the responsibility of the designer to ensure that: — functional requirements are properly defined; — the geometrical features influencing the functions are properly specified; — the entire part, i.e. all geometrical features, is completely and unambiguously specified. General geometrical specification and general size specification are ways of minimising the number of indications in a TPD.
5.2 Rule for the applicability of the general geometrical specification Rule D: the general geometrical specification shall apply to each integral feature independently on the product, with the following exceptions (see Figure 3 ): 1) an integral feature specified by a size specification (individual size specification or general size specification); 2) an integral feature or its derived feature specified by an individual geometrical specification; 3) a datum feature used in the datum system defined in the datum section of the general geometrical specification (see 5.3); 4) an integral feature indicated with simplified representation and not included in the CAD model, for example edges, fillets or screw threads. NOTE 1 General geometrical specification applies to integral features irrespective of a surface texture specification. NOTE 2 The general geometrical specifications are in accordance with the independency principle and the feature principle. NOTE 3 When individual specifications are applied on one or more portions of a single integral feature, any other portion is considered as another integral feature.