SIST EN ISO 5459:2011
(Main)Geometrical product specifications (GPS) - Geometrical tolerancing - Datums and datum systems (ISO 5459:2011)
Geometrical product specifications (GPS) - Geometrical tolerancing - Datums and datum systems (ISO 5459:2011)
This International Standard specifies terminology, rules and methodology for the indication and understanding of datums and datum systems in technical product documentation. This International Standard also provides explanations to assist the user in understanding the concepts involved. This International Standard defines the specification operator (see ISO 17450-2) used to establish a datum or datum system. The verification operator (see ISO 17450-2) can take different forms (physically or mathematically) and is not the subject of this International Standard.
Geometrische Produktspezifikation (GPS) - Geometrische Tolerierung - Bezüge und Bezugssysteme (ISO 5459:2011)
ISO 5459 beschreibt die Begriffe, die Regeln, Erklärungen und die Art und Weise, in der Bezüge und Bezugssysteme in technische Produktdokumente eingetragen werden.
ANMERKUNG Detaillierte Regeln zur Maximum- und Minimum-Material-Bedingung sind in ISO 2692 enthalten
Spécification géométrique des produits (GPS) - Tolérancement géométrique - Références spécifiées et systèmes de références spécifiées (ISO 5459:2011)
L'ISO 5459:2011 spécifie la terminologie, les règles et la méthodologie pour indiquer les références spécifiées et les systèmes de références spécifiées dans la documentation technique de produits. Elle fournit également des explications aidant l'utilisateur à la compréhension des concepts considérés.
L'ISO 5459:2011 définit l'opérateur de spécification utilisé pour établir une référence spécifiée ou un système de références spécifiées. L'opérateur de vérification qui peut prendre différentes formes (physique ou mathématique) ne fait pas l'objet de l'ISO 5459:2011.
Specifikacija geometrijskih veličin izdelka - Geometrijsko toleriranje - Reference in sistemi referenc (ISO 5459:2011)
Ta mednarodni standard določa terminologijo, pravila in metodologijo za indikacijo in razumevanje referenc in sistemov referenc v tehnični dokumentaciji proizvoda. Ta mednarodni standard prav tako zagotavlja pojasnila za pomoč uporabniku pri razumevanju vpletenih konceptov. Ta mednarodni standard določa operaterja specifikacij (glej ISO 17450-2), ki se uporablja za vzpostavitev reference ali sistema referenc. Operater specifikacije (glej ISO 17450-2) lahko prevzame različne oblike (fizične ali matematične) in ni predmet tega mednarodnega standarda.
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Standards Content (Sample)
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Geometrische Produktspezifikation (GPS) - Geometrische Tolerierung - Bezüge und Bezugssysteme (ISO 5459:2011)Spécification géométrique des produits (GPS) - Tolérancement géométrique - Références spécifiées et systèmes de références spécifiées (ISO 5459:2011)Geometrical product specifications (GPS) - Geometrical tolerancing - Datums and datum systems (ISO 5459:2011)17.040.40Geometrical Product Specification (GPS)17.040.10Tolerance in ujemiLimits and fitsICS:Ta slovenski standard je istoveten z:EN ISO 5459:2011SIST EN ISO 5459:2011en,fr01-oktober-2011SIST EN ISO 5459:2011SLOVENSKI
STANDARDSIST ISO 5459:19951DGRPHãþDSIST EN ISO 5459:2011
EUROPEAN STANDARD NORME EUROPÉENNE EUROPÄISCHE NORM
EN ISO 5459
August 2011 ICS 01.100.20; 17.040.10 English Version
Geometrical product specifications (GPS) - Geometrical tolerancing - Datums and datum systems (ISO 5459:2011)
Spécification géométrique des produits (GPS) - Tolérancement géométrique - Références spécifiées et systèmes de références spécifiées (ISO 5459:2011)
Geometrische Produktspezifikation (GPS) - Geometrische Tolerierung - Bezüge und Bezugssysteme (ISO 5459:2011)This European Standard was approved by CEN on 18 May 2011.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management Centre has the same status as the official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATIONCOMITÉ EUROPÉEN DE NORMALISATION EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre:
Avenue Marnix 17,
B-1000 Brussels © 2011 CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Members. Ref. No. EN ISO 5459:2011: ESIST EN ISO 5459:2011
EN ISO 5459:2011 (E) 2 Contents Page Foreword ..............................................................................................................................................................3 SIST EN ISO 5459:2011
EN ISO 5459:2011 (E) 3 Foreword This document (EN ISO 5459:2011) has been prepared by Technical Committee ISO/TC 213 "Dimensional and geometrical product specifications and verification" in collaboration with Technical Committee CEN/TC 290 “Dimensional and geometrical product specification and verification” the secretariat of which is held by AFNOR. This European Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by February 2012, and conflicting national standards shall be withdrawn at the latest by February 2012. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights. According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and the United Kingdom. Endorsement notice The text of ISO 5459:2011 has been approved by CEN as a EN ISO 5459:2011 without any modification.
SIST EN ISO 5459:2011SIST EN ISO 5459:2011
Reference numberISO 5459:2011(E)© ISO 2011
INTERNATIONAL STANDARD ISO5459Second edition2011-08-15Geometrical product specifications (GPS) — Geometrical tolerancing — Datums and datum systems Spécification géométrique des produits (GPS) — Tolérancement géométrique — Références spécifiées et systèmes de références spécifiées
SIST EN ISO 5459:2011ISO 5459:2011(E)
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ISO 2011 All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or ISO's member body in the country of the requester. ISO copyright office Case postale 56 • CH-1211 Geneva 20 Tel.
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SIST EN ISO 5459:2011
ISO 5459:2011(E) © ISO 2011 – All rights reserved iii Contents Page Foreword............................................................................................................................................................iv Introduction.........................................................................................................................................................v 1 Scope......................................................................................................................................................1 2 Normative references............................................................................................................................1 3 Terms and definitions...........................................................................................................................2 4 Symbols..................................................................................................................................................6 5 Role of datums.......................................................................................................................................7 6 General concepts..................................................................................................................................9 6.1 General...................................................................................................................................................9 6.2 Intrinsic characteristics of surfaces associated with datum features...........................................10 6.2.1 General.................................................................................................................................................10 6.2.2 A single datum established from a single feature...........................................................................10 6.2.3 Common datum established from two or more single features simultaneously..........................10 6.2.4 Datum systems established in a defined sequence from two or more single features...............12 6.3 Single datums, common datums and datum systems....................................................................12 6.3.1 General.................................................................................................................................................12 6.3.2 Single datums......................................................................................................................................12 6.3.3 Common datums.................................................................................................................................14 6.3.4 Datum systems....................................................................................................................................14 7 Graphical language.............................................................................................................................17 7.1 General.................................................................................................................................................17 7.2 Indication of datum features..............................................................................................................17 7.2.1 Datum feature indicator......................................................................................................................17 7.2.2 Datum feature identifier......................................................................................................................18 7.2.3 Datum targets......................................................................................................................................18 7.3 Specification of datums and datum systems...................................................................................21 7.4 Indication and meaning of rules........................................................................................................21 7.4.1 General.................................................................................................................................................21 7.4.2 Rules.....................................................................................................................................................22 Annex A (normative)
Association for datums................................................................................................37 Annex B (informative)
Invariance classes......................................................................................................47 Annex C (informative)
Examples.....................................................................................................................49 Annex D (informative)
Former practices.........................................................................................................71 Annex E (informative)
Examples of a datum system or a common datum established with contacting features.............................................................................................................................73 Annex F (normative)
Relations and dimensions of graphical symbols......................................................79 Annex G (informative)
Relationship to the GPS matrix model.....................................................................80 Bibliography......................................................................................................................................................81
SIST EN ISO 5459:2011ISO 5459:2011(E) iv © ISO 2011 – All rights reserved Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO 5459 was prepared by Technical Committee ISO/TC 213, Dimensional and geometrical product specification and verification. This second edition cancels and replaces the first edition (ISO 5459:1981), which has been technically revised. SIST EN ISO 5459:2011
ISO 5459:2011(E) © ISO 2011 – All rights reserved v Introduction ISO 5459 is a geometrical product specification (GPS) standard and is to be regarded as a general GPS standard (see ISO/TR 14638). It influences the chain links 1 to 3 of the chain of standards on datums. The ISO/GPS Masterplan given in ISO/TR 14638 gives an overview of the ISO/GPS system of which this standard is a part. The fundamental rules of ISO/GPS given in ISO 8015 apply to this standard and the default decision rules given in ISO 14253-1 apply to specifications made in accordance with this standard unless otherwise indicated. For more detailed information of the relation of this International Standard to the GPS matrix model, see Annex G. For the definitive presentation (proportions and dimensions) of symbols for geometrical tolerancing, see ISO 7083. The previous version of ISO 5459 dealt only with planes, cylinders and spheres being used as datums. There is a need to consider all types of surfaces, which are increasingly used in industry. The definitions of classes of surfaces as given in Annex B are exhaustive and unambiguous. This edition of ISO 5459 applies new concepts and terms that have not been used in previous ISO GPS standards. These concepts are described in detail in ISO/TR 14638, ISO 17450-1 and ISO 17450-2; therefore, it is recommended to refer to these standards when using ISO 5459. This International Standard provides tools to express location or orientation constraints, or both, for a tolerance zone. It does not provide information about the relationship between datums or datum systems and functional requirements or applications.
SIST EN ISO 5459:2011SIST EN ISO 5459:2011
INTERNATIONAL STANDARD ISO 5459:2011(E) © ISO 2011 – All rights reserved 1 Geometrical product specifications (GPS) — Geometrical tolerancing — Datums and datum systems 1 Scope This International Standard specifies terminology, rules and methodology for the indication and understanding of datums and datum systems in technical product documentation. This International Standard also provides explanations to assist the user in understanding the concepts involved. This International Standard defines the specification operator (see ISO 17450-2) used to establish a datum or datum system. The verification operator (see ISO 17450-2) can take different forms (physically or mathematically) and is not the subject of this International Standard. NOTE The detailed rules for maximum and least material requirements for datums are given in ISO 2692. 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. ISO 128-24:1999, Technical drawings — General principles of presentation — Part 24: Lines on mechanical engineering drawings ISO 1101:2004, Geometrical Product Specifications (GPS) — Geometrical tolerancing — Tolerances of form, orientation, location and run-out ISO 1101:2004/Amd 1:—1), Geometrical Product Specifications (GPS) — Geometrical tolerancing — Tolerances of form, orientation, location and run-out — Amendment 1: Representation of specifications in the form of a 3D model ISO 2692:2006, Geometrical product specifications (GPS) — Geometrical tolerancing — Maximum material requirement (MMR), least material requirement (LMR) and reciprocity requirement (RPR) ISO 3098-0, Technical product documentation — Lettering — Part 0: General requirements ISO 3098-5, Technical product documentation — Lettering — Part 5: CAD lettering of the Latin alphabet, numerals and marks ISO 14660-1:1999, Geometrical Product Specifications (GPS) — Geometrical features — Part 1: General terms and definitions 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 and uncertainties ISO 81714-1, Design of graphical symbols for use in the technical documentation of products — Part 1: Basic rules
1) To be published. SIST EN ISO 5459:2011ISO 5459:2011(E) 2 © ISO 2011 – All rights reserved 3 Terms and definitions For the purposes of this document, the terms and definitions given in ISO 1101, ISO 2692, ISO 14660-1, ISO 17450-1, ISO 17450-2 and the following apply. 3.1 situation feature point, straight line, plane or helix from which the location and orientation of features, or both, can be defined 3.2 datum feature real (non-ideal) integral feature used for establishing a datum NOTE 1 A datum feature can be a complete surface, a portion of a complete surface, or a feature of size. NOTE 2 An illustration showing the relations between datum feature, associated feature and datum is given in Figure 4. 3.3 associated feature associated feature for establishing a datum ideal feature which is fitted to the datum feature with a specific association criterion NOTE 1 The type of the associated feature is by default the same as the type of the nominal integral feature used to establish the datum (for an exception see 7.4.2.5). NOTE 2 The associated feature for establishing a datum simulates the contact between the real surface of the workpiece and other components. NOTE 3 An illustration showing the relations between datum feature, associated feature and datum is given in Figure 4. 3.4 datum one or more situation features of one or more features associated with one or more real integral features selected to define the location or orientation, or both, of a tolerance zone or an ideal feature representing for instance a virtual condition NOTE 1 A datum is a theoretically exact reference; it is defined by a plane, a straight line or a point, or a combination thereof. NOTE 2 The concept of datums is inherently reliant upon the invariance class concept (see Annex A and Annex B). NOTE 3
Datums with maximum material condition (MMC) or least material condition (LMC) are not covered in this International Standard (see ISO 2692). NOTE 4 When a datum is established, for example, on a complex surface, the datum consists of a plane, a straight line or a point, or a combination thereof. The modifier [SL], [PL] or [PT], or a combination thereof, can be attached to the datum letter to limit the situation feature(s) taken into account relative to the surface. NOTE 5 An illustration showing the relation between datum feature, associated feature and datum is given in Figure 4. 3.5 primary datum datum that is not influenced by constraints from other datums 3.6 secondary datum datum, in a datum system, that is influenced by an orientation constraint from the primary datum in the datum system SIST EN ISO 5459:2011
ISO 5459:2011(E) © ISO 2011 – All rights reserved 3 3.7 tertiary datum datum, in a datum system, that is influenced by constraints from the primary datum and the secondary datum in the datum system 3.8 single datum datum established from one datum feature taken from a single surface or from one feature of size NOTE The invariance class of a single surface can be complex, prismatic, helical, cylindrical, revolute, planar or spherical. A set of situation features defining the datum (see Table B.1) corresponds to each type of single surface. 3.9 common datum datum established from two or more datum features considered simultaneously NOTE To define a common datum, it is necessary to consider the collection surface created by the considered datum features. The invariance class of a collection surface can be complex, prismatic, helical, cylindrical, revolute, planar or spherical (see Table B.1). 3.10 datum system set of two or more situation features established in a specific order from two or more datum features NOTE To define a datum system, it is necessary to consider the collection surface created by the considered datum features. The invariance class of a collection surface can be complex, prismatic, helical, cylindrical, revolute, planar or spherical (see Table B.1). 3.11 datum target portion of a datum feature which can nominally be a point, a line segment or an area NOTE Where the datum target is a point, a line or an area, it is indicated as a datum target point, a datum target line or a datum target area, respectively. 3.12 moveable datum target datum target with a controlled motion 3.13 collection surface two or more surfaces considered simultaneously as a single surface NOTE 1 Table B.1 is used to determine the invariance class of a datum or datum systems when using a collection of surfaces. NOTE 2 Two intersecting planes may be considered together or separately. When the two intersecting planes are considered simultaneously as a single surface, that surface is a collection surface. 3.14 feature of size geometrical shape defined by a linear or angular dimension which is a size NOTE The features of size can be a cylinder, a sphere, two parallel opposite surfaces, a cone or a wedge. [ISO 14660-1:1999, 2.2] NOTE In this International Standard, features which are not features of size according to ISO 14660-1 are used to establish a datum as a feature of size, e.g. a truncated sphere (see the example in C.1.4). SIST EN ISO 5459:2011
ISO 5459:2011(E) 4 © ISO 2011 – All rights reserved 3.15 objective function objective function for association formula that describes the quality of association NOTE 1 In this International Standard, the term “objective function” refers to “objective function for association”. NOTE 2 The objective functions are usually named and mathematically described: maximum inscribed, minimum zone, etc. 3.16 association operation used to fit ideal feature(s) to non-ideal feature(s) according to an association criterion [ISO 17450-1:—, 3.2] 3.17 constraint limitation on the associated feature EXAMPLE Orientation constraint, location constraint, material constraint or intrinsic characteristic constraint. 3.17.1 orientation constraint limitation to one or more rotational degrees of freedom 3.17.2 location constraint limitation to one or more translational degrees of freedom 3.17.3 material constraint additional condition to the location of the associated feature, relative to the material of the feature, while optimizing an objective function NOTE For example, an association constraint can be that all distances between the associated feature and the datum feature are positive or equal to zero, i.e. the associated feature is outside the material. 3.17.4 intrinsic characteristic constraint additional requirement applied to the intrinsic characteristic of an associated feature whether it is considered fixed or variable 3.18 association criterion objective function with or without constraints, defined for an association NOTE 1 Several constraints may be defined for an association. NOTE 2 Association results (associated features) may differ, depending upon the choice of association criterion. NOTE 3 Default association criteria are defined in Annex A. 3.19 integral feature surface or line on a surface NOTE An integral feature is intrinsically defined. [ISO 14660-1:1999, 2.1.1] SIST EN ISO 5459:2011
ISO 5459:2011(E) © ISO 2011 – All rights reserved 5 3.20 contacting feature ideal feature of any type which is different from the nominal feature under consideration and is associated with the corresponding datum feature See Figure 1.
Contacting feature on nominal model b)Contacting feature on real workpiece Key 1 contacting feature: ideal sphere in contact with the datum feature or the feature under consideration 2 features under consideration: nominal trapezoidal slot (collection of two non-parallel surfaces) 3 datum feature: real feature corresponding to the trapezoidal slot (collection of two non-parallel surfaces) Figure 1 — Example of a contacting feature 3.21 invariance class group of ideal features for which the nominal surface is invariant for the same degrees of freedom NOTE There are seven invariance classes (see Annex B). 3.22 theoretically exact dimension TED dimension indicated on technical product documentation, which is not affected by an individual or general tolerance NOTE 1 For the purpose of this International Standard, the term “theoretically exact dimension” has been abbreviated TED. NOTE 2 A theoretically exact dimension is a dimension used in an operation (e.g. association, partition, collection, …). NOTE 3 A theoretically exact dimension can be a linear dimension or an angular dimension.
NOTE 4 A TED can define ⎯ the extension or the relative location of a portion of one feature,
⎯ the length of the projection of a feature, ⎯ the theoretically exact orientation or location of one feature relative to one or more other features, or ⎯ the nominal shape of a feature. NOTE 5 A TED is indicated by a value in a rectangular frame. [ISO 1101:2004/Amd 1:—, 3.7] SIST EN ISO 5459:2011
ISO 5459:2011(E) 6 © ISO 2011 – All rights reserved 4 Symbols Table 1 gives symbols to identify the datum feature or datum target used to establish a datum. Table 2 gives the list of modifier symbols, which can be associated the datum letter. Table 1 — Datum features and datum target symbols Description Symbol Subclause Datum feature indicator
7.2.1 Datum feature identifier Capital letter (A, B, C, AA, etc.) 7.2.2 Single datum target frame
7.2.3.2 Moveable datum target frame7.2.3.2 Datum target point
7.2.3.3 Closed datum target line
7.2.3.3 Non-closed datum target line
7.2.3.3 Datum target area
7.2.3.3
SIST EN ISO 5459:2011
ISO 5459:2011(E) © ISO 2011 – All rights reserved 7 Table 2 — Modifier symbols Symbol Description Subclause [PD] Pitch diameter 7.4.2.1 [MD] Major diameter 7.4.2.1 [LD] Minor diameter 7.4.2.1 [ACS] Any cross section 7.4.2.4 [ALS] Any longitudinal section 7.4.2.4 [CF] Contacting feature 7.4.2.5 [DV] Variable distance (for common datum) 7.4.2.7 [PT] (situation feature of type) Point 7.4.2.8 [SL] (situation feature of type) Straight line 7.4.2.8 [PL] (situation feature of type) Plane 7.4.2.8
>< For orientation constraint only 7.4.2.8Projected (for secondary or tertiary datum) 7.4.2.10
Least material requirement See ISO 2692
Maximum material requirement See ISO 2692
5 Role of datums Datums form part of a geometrical specification (see ISO 1101). Datums are established from real surfaces identified on a workpiece. Datums allow tolerance zones to be located or orientated (see Examples 1 and 2) and virtual conditions to be defined (for example maximum material virtual condition # according to ISO OS9O). The datums can be seen as a means to lock degrees of freedom of a tolerance zone. The number of degrees of freedom of the tolerance zone which are locked depends on the nominal shape of the features utilized to establish the datum or datum system; whether the datum is primary, secondary or tertiary; and on the toleranced characteristic indicated in the geometrical tolerance frame. By default, a datum locks all the degrees of freedom of the tolerance zone that it can lock given its shape and which ⎯ are required by the geometrical characteristic indicated in the tolerance frame, and ⎯ have not already been locked by the preceding datum(s) in the datum system. When a datum locks only orientation degrees of freedom, this shall be indicated by the modifier ><. EXAMPLE 1 The tolerance zone, which is the space between two parallel planes 0,1 mm apart, is constrained in orientation by a 75° theoretically exact angle from the datum. Here, the datum is the situation feature of a cylinder (axis of associated cylinder). See Figure 2. SIST EN ISO 5459:2011
ISO 5459:2011(E) 8 © ISO 2011 – All rights reserved Dimensions in millimetresIndication on the drawing b)
Illustration of tolerance zone Key 1 datum A constituted by the axis of the associated cylinder Figure 2 — Example of tolerance zone constrained in orientation from a datum EXAMPLE 2 The tolerance zone, which is the space between two parallel planes 0,2 mm apart, is constrained in orientation by a 70° angle from a datum, and in location by the distance 20 mm from the gauge plane positioned perpendicular to the axis of 40° cone where its local diameter is 30 mm. Here, the datum consists of the set of situation features of the cone with a fixed angle of 40°, i.e. the cone axis and the point of intersection between the gauge plane and that axis. See Figure 3. Dimensions in millimetres
Indication on the drawing b)Illustration of tolerance zone Key 1 datum A constituted by the axis of the associated cone, the point of intersection of the gauging plane and this axis Figure 3 — Example of a tolerance zone constrained in location from a datum SIST EN ISO 5459:2011
ISO 5459:2011(E) © ISO 2011 – All rights reserved 9 6 General concepts 6.1 General Datums and datum systems are theoretically exact geometric features used together with implicit or explicit TEDs to locate or orientate a) tolerance zones for toleranced features, or b) virtual conditions, e.g. in the case of maximum material requirement (see ISO 2692). A datum consists of a set of situation features for an ideal feature (feature of perfect form). This ideal feature is an associated feature which is established from the identified datum features of a workpiece. Datum features may be complete features, or identified portions thereof (see Clause 7). A datum system consists of more than one datum. The geometrical type of these associated features belongs to one of t
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