Detail of GB/T 38762.2-2020

Introduction of GB/T 38762.2-2020

Codeofchina.com is in charge of this English translation. In case of any doubt about the English translation, the Chinese original shall be considered authoritative. GB/T 38762 consists of the following parts, under the general title Geometrical product specification (GPS) - Dimensional tolerancing: ——Part 1: Linear sizes; ——Part 2: Dimensions other than linear or angular sizes; ——Part 3: Angular sizes. This is Part 2 of GB/T 38762. This part is developed in accordance with the rules given in GB/T 1.1-2009. This standard has been redrafted and modified in relation to ISO 14405-2:2018 Geometrical product specifications (GPS) - Dimensional tolerancing - Part 2: Dimensions other than linear or angular sizes. The main technical differences with respect to ISO 14405-2: 2018 are as follows: ——As for the normative references, adjustments of technical nature have been made to this part to keep them in line with the technical conditions in China. The adjustment situations are embodied in a concentrated way in Clause 2 "Normative references" and the specific adjustments are as follows:  ISO 1101 is replaced by GB/T 1182, which is modified in relation to the international standard;  ISO 8015 is replaced by GB/T 4249, which is modified in relation to the international standard;  ISO 13715 is replaced by GB/T 19096, which is identical to the international standard;  ISO 17450-1 is replaced by GB/T 24637.1, which is modified in relation to the international standard;  ISO 17450-2 is replaced by GB/T 24637.2, which is modified in relation to the international standard;  ISO 17450-3 is replaced by GB/T 24637.3, which is modified in relation to the international standard;  ISO 14405-1 is replaced by GB/T 38762.1, which is modified in relation to the international standard;  ISO 14405-3 is replaced by GB/T 38762.3, which is modified in relation to the international standard. This part was proposed by and is under the jurisdiction of National Technical Committee on Geometrical Product Specifications of Standardization Administration of China (SAC/TC 240). Geometrical product specifications (GPS) - Dimensional Tolerancing - Part 2: Dimensions other than linear or angular sizes 1 Scope This part of GB/T 38762 illustrates the ambiguity caused by the use of dimensional specifications to control properties other than linear or angular size and the benefit of using geometrical specifications instead. Dimensional tolerancing may be indicated by ± tolerancing or geometrical specifications. The ambiguity caused by using ± tolerances for dimensions other than linear sizes (for individual tolerances and general tolerances according to, e.g.GB/T 1804 and GB/T 6414) is explained in Annex A. Note 1: The figures, as shown in this document, merely illustrate the text and are not intended to reflect actual usage. The figures are consequently simplified to indicate only the relevant principles. Note 2: For indications of dimensional specifications, see the following: ——GB/T 38762.1 for linear size; ——GB/T 38762.3 for angular size; ——ISO 2538-1 and ISO 2538-2 for wedges; ——GB/T 15754 for cones. Note 3: The rules for geometrical specifications are given in GB/T 1182. 2 Normative References The following referenced documents are indispensable for the application 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. GB/T 1182 Geometrical product specifications(GPS) - Geometrical tolerancing - Tolerances of form ,orientation, location and run-out (GB/T 1182-2018，ISO 1101:2017, MOD) GB/T 4249 Geometrical product specifications (GPS) - Fundamentals - Concepts, principles and rules (GB/T 4249-2018, ISO 8015:2011, MOD) GB/T 19096 Technical drawing-Drawing presentation-Vocabulary and indications for edges of undefined shape (GB/T 19096-2003, ISO 13715-2000, IDT) GB/T 24637.1 Geometrical product specifications (GPS) - General concepts - Part 1: Model for geometrical specification and verification (GB/T 24637.1-2020, ISO 17450-1:2011, MOD) GB/T 24637.2 Geometrical product specifications (GPS) - General concepts - Part 2: Basic tenets, specifications, operators, uncertainties and ambiguities (GB/T 24637.2-2020, ISO 17450-2:2012, MOD) GB/T 24637.3 Geometrical product specifications (GPS) - General concepts - Part 3: Toleranced features (GB/T 24637.3-2020, ISO 17450-3:2016, MOD) GB/T 38762.1 Geometrical product specifications (GPS) - Dimensional tolerancing - Part 1: Linear sizes (GB/T 38762.1-2020, ISO 14405-1:2016, MOD) GB/T 38762.3 Geometrical product specifications(GPS) - Dimensional tolerancing - Part 3:Angular sizes (GB/T 38762.3-2020，ISO 14405-3:2016, MOD) ISO 129-1 Technical product documentation (TPD) - Presentation of dimensions and tolerances - Part 1:General principles 3 Terms and Definitions For the purposes of this document, the terms and definitions given in GB/T 1182, GB/T 4249, GB/T 19096, GB/T 24637.1, GB/T 24637.2, GB/T 24637.3, GB/T 38762.1, GB/T 38762.3, ISO 129-1 and the following apply. Note: The term “drawing” is used in this document as a synonym for the 2D drawing, the 3D model and other representations of the workpiece. 3.1 ± tolerancing tolerancing using dimension and indication of limit deviations, dimension limit values or unilateral dimension limit Note: The sign ± should not be understood in a way that the limit deviations are always symmetrical to the nominal size. 3.2 linear size dimension in length units characterizing a feature of size 3.3 angular size dimension in angle units characterizing a feature of size 3.4 distance dimension between two geometrical features which are not considered as a feature of size Note 1: Distance may be between two integral features or an integral feature and a derived feature or two derived features. Note 2: Linear distance and angular distance exist. 3.4.1 linear distance distance in length units 3.4.2 angular distance distance in angle units 4 Principles and rules for indication of dimensions and related tolerances The general rules and principles for indicating ± tolerances given in GB/T 38762.1 apply to this document and are the basis for nominal tolerancing on mechanical engineering drawings. In all other cases, special rules apply. For rules on the indication of units, see Clause 5. For dimensions other than linear or angular sizes, a requirement with ± tolerancing is ambiguous (specification ambiguity) when applied to a real workpiece. This type of specification is not recommended; see Annex A. Specification ambiguity of dimensional specifications may be avoided for linear features of size when specified in accordance with GB/T 38762.1 and for angular features of size when specified in accordance with GB/T 38762.3. In order to minimize specification ambiguity, geometrical specifications shall be used for the cases illustrated in Table 1. Unless otherwise specified, e.g. by using CZ according to GB/T 1182 or ○M according to GB/T 16671, tolerances on mechanical engineering drawings are independent requirements without any relationships to other requirements for the same feature(s). This is the independency principle (see GB/T 4249).

Contents of GB/T 38762.2-2020

Foreword i 1 Scope 2 Normative References 3 Terms and Definitions 4 Principles and rules for indication of dimensions and related tolerances 5 Units used in drawings for dimensions 6 Indication of tolerances for linear or angular sizes 7 Illustrations of ambiguous ± tolerancing v.s. unambiguous geometrical specifications 8 Angular tolerancing Annex A (Informative) Explanations and examples of the ambiguity caused by using ± tolerances for dimensions other than linear size or angular size Annex B (Informative) Relation to the GPS matrix model Bibliography