EN ISO 5459:2011

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 5459:19951DGRPHãþD

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.
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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
ISO 5459:2011(E)
©
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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ii © ISO 2011 – All rights reserved
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
ISO 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.
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 5459:2011

ISO 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.
a)
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 frame
7.2.3.2 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
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 7.4.2.8
Projected (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 millimetres
a)
Indication 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
a)
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 the following invariance classes: ⎯ spherical (i.e. a sphere); ⎯ planar (i.e. a plane); ⎯ cylindrical (i.e. a cylinder); ⎯ helical (e.g. a threaded surface)2); ⎯ revolute (e.g. a cone or a torus); ⎯ prismatic (e.g. a prism); ⎯ complex (e.g. a free-form surface). Each single or collection feature belongs to one invariance class (for an explanation of invariance classes, invariance degree, and degree of freedom, see Annex B). Associated features are established from the real or extracted single features used for the datum. The associated feature can be defined by an operation of association including constraints coming from the feature itself or from one or more other features. The situation features that make up the datum are defined from these associated features. The default association methods are given in Annex A. One or more single features can be used to establish a datum. If only one single feature is used, it establishes a single datum. If more than one single feature is used, they can either be considered simultaneously to establish a common datum or in a predefined order to establish a datum system (see 6.3). The datum feature(s) to be used for establishing each datum shall be designated and identified. The single datums (see 6.3.2), common datums (see 6.3.3) or datum systems (see 6.3.4), as applicable, shall be specified for each geometrical specification. When applicable, any additional constraints shall be defined for the association.
2) Helical surfaces as such are not considered in this International Standard. They are regarded as cylindrical surfaces because, in most functional cases where helical surfaces (threads, helical slope, endless screw, etc.) are involved, the combined rotation and translation of the helix is not needed for datum purposes. In these cases, the pitch cylinder surface is used to establish the datum. The major or minor cylindrical surface can also be considered and specified. SIST EN ISO 5459:2011

ISO 5459:2011(E) 10 © ISO 2011 – All rights reserved NOTE Datums and datum systems are geometrical features, not coordinate systems. Coordinate systems can be built on datums, but this International Standard does not provide the means to express them. EXAMPLE In Figure 4, the datum is indicated as a single datum derived from a nominal feature, a cylinder, used to orientate or locate a tolerance zone. In order to derive the datum, the following sequence of operations is performed: ⎯ a partition to define the real integral surface corresponding to the nominal feature [see Figure 4 b)]; ⎯ an extraction to provide the extracted integral feature [see Figure 4 c)]; ⎯ a filtration (see Annex A); ⎯ an association (see Annex A for association method) to define the associated feature. (In this case, its type is the same as the nominal feature.) The associated feature [see Figure 4 d)] is established from the non-ideal surface (in the specification process) or from the extracted feature (in the verification process). The datum is defined as the situation feature (the axis) of the associated cylinder [see Figure 4 e)]. 6.2 Intrinsic characteristics of surfaces associated with datum features 6.2.1 General The default intrinsic characteristic constraint (variable or fixed) shall be as defined in 6.2.2, 6.2.3 or 6.2.4. For datums with virtual conditions, see ISO 2692:2006. 6.2.2 A single datum established from a single feature The intrinsic characteristic constraints for a single feature of size are, by default, variable for linear sizes but theoretically exact for the angular dimensions or for dimensions which are not sizes (see Table 3 and 7.4.2.2). EXAMPLE For a cone, by default, the angle is considered a theoretically exact angle. For a torus, by default, the cross-section diameter is considered a variable (size of torus), but the median ring diameter of the axis should be considered theoretically exact. Table 3 — Default status of intrinsic characteristics of features of size Feature of size Invariance class Intrinsic characteristic Default status Cylinder cylindrical diameter Variable See example in C.1.2. Sphere spherical diameter Variable See example in C.1.4. Two parallel opposite planes planar distance between the two planes Variable See example in C.1.10. Cone revolute angle Theoretically exact See example in C.1.3. Wedge prismatic angle Theoretically exact See example in C.1.9.
6.2.3 Common datum established from two or more single features simultaneously The intrinsic characteristics of each associated feature establishing the common datum shall be considered as in 6.2.2. Intrinsic characteristics introduced by the collection of features (defining the relation between the associated features) shall by default be considered theoretically exact for both linear and angular dimensions.
ISO 5459:2011(E) © ISO 2011 – All rights reserved 11
a)
Drawing indication
b)
Integral real surface of the workpiece
c)
Extraction
d)
Association
e)
Datum Key 1 tolerance frame to be linked to a toleranced feature 2 nominal integral feature (which is a feature of size) 3 nominal derived feature 4 real integral feature (datum feature in this case) 5 extracted integral feature (optional) 6 associated integral feature 7 derived feature of associated integral feature 8 single datum (situation feature of the associated surface) In the example shown in Figure 4 e), the derived feature (key 7) and the situation feature (key 8) are the same as each other; however, this is not always the case. Figure 4 — Illustration of features used for establishing a single datum from a cylinder SIST EN ISO 5459:2011

ISO 5459:2011(E) 12 © ISO 2011 – All rights reserved EXAMPLE A common datum is established from two parallel non-coaxial cylinders (invariance class: prismatic). Each individual cylinder has an intrinsic characteristic, its diameter. The collection of features also has intrinsic characteristics: an angle, defined by the fact that two axes restrict the twist of the datum, and the distance between the two axes (see C.2.4). The two diameters of the cylinders are considered by default variable and the twist angle and the distance between the two are considered theoretically exact. NOTE See also 6.3.3, 7.4.2.7 and 7.4.2.9 for the special case where the linear dimensions between features included in the collection can be considered variable by using the modifier [DV]. 6.2.4 Datum systems established in a defined sequence from two or more single features
The intrinsic characteristics of each associated feature establishing the datum system shall be considered as in 6.2.2. The intrinsic characteristics introduced by the collection of features (defining the relation between the associated features) shall be considered variable for linear dimensions but theoretically exact for the angular dimensions. 6.3 Single datums, common datums and datum systems 6.3.1 General When a single surface or a collection surface is identified as a datum feature, the invariance degrees for which the surface is invariant shall be identified and compared with Table B.1 in order to determine the set of situation features (point, straight line, plane or helix, or a combination thereof) that constitutes the datum. 6.3.2 Single datums A single datum consists of one or more situation features based on one single feature or a portion thereof. NOTE A single datum taken from a cone has two situation features: its axis and a point on that axis. EXAMPLE Single datum taken from a cylinder or a plane. SIST EN ISO 5459:2011

ISO 5459:2011(E) © ISO 2011 – All rights reserved 13 Indication of datum feature Indication of datum in tolerance frameIllustration of the meaning Invariance class and situation feature (see Annex B) Datum
Cylindrical
Axis of associated cylinder
Planar
Associated plane Key 1 associated feature (without orientation constraint) 2 straight line which is the situation feature of the associated cylinder (its axis) 3 plane which is the situation feature of the associated plane (the associated plane itself) NOTE Association for single datums is described in Annex A.
If a single datum is used as the only datum in a tolerance frame, or if it is the primary datum in a datum system, the associated feature to the real integral feature (or to the portions of it) used for establishing the datum is obtained without external orientation constraints or location constraints.
For the constraints that are applied, when a single datum is used as a “secondary datum” or a “tertiary datum”, see 6.3.4. Additional examples of single datums are given in C.1. For a feature of size made up of two opposite parallel planes, the collection surface associated with the surfaces (or to the portions of the surfaces) used for establishing the datum is obtained with an internal orientation constraint; the associated surfaces (constituting the collection surface) are individually defined with an internal parallelism constraint and a variable intrinsic characteristic constraint (see C.1.10). A secondary datum shall not be specified when it does not constrain more degrees of freedom of the tolerance zone than the primary datum. A tertiary datum shall not be specified when it does not constrain more degrees of freedom of the tolerance zone than the primary and the secondary datums. SIST EN ISO 5459:2011

ISO 5459:2011(E) 14 © ISO 2011 – All rights reserved 6.3.3 Common datums A common datum consists of one or more situation features established by taking into account the collection surface. If the common datum is used as the only datum in a tolerance frame, or if it is the primary datum in a datum system, the collection of associated features used for establishing the datums, is established without external orientation constraints or location constraints; therefore, the surfaces (constituting the collection surface) are associated together, simultaneously. For the constraints that are applied when a common datum is used as a “secondary datum” or a “tertiary datum”, see 6.3.4. A secondary datum shall not be specified when it does not constrain more degrees of freedom of the tolerance zone than the primary datum. A tertiary datum shall not be specified when it does not constrain more degrees of freedom of the tolerance zone than the primary and the secondary datums. Examples of common datums are given in 6.3.4 (Examples 1 and 2 illustrate the difference between a datum system and a common datum) and C.2. The complementary indication [DV] (meaning “distance variable”) following the letters indicating a common datum in a tolerance frame means that the linear dimensions between the situation features are variable. See also 7.4.2.9 and E.4. 6.3.4 Datum systems A datum system is constituted by an ordered sequence of two or three single or common datums. A datum system consists of two or three situation features resulting from the collection of the considered surfaces. The associated features used to establish the datum system are derived sequentially, in the order defined by the geometrical specification. The relative orientation of the associated surfaces is theoretically exact but their relative location is variable. This order defines the orientation constraints for the association operation: the primary datum imposes orientation constraints on the secondary datum and tertiary datum; the secondary datum imposes orientation constraints on the tertiary datum. A secondary datum shall be specified when it is necessary to constrain more degrees of freedom of the tolerance zone than are constrained by the primary datum. A tertiary datum shall be specified when it is necessary to constrain more degrees of freedom of the tolerance zone than are constrained by the primary and the secondary datums. A secondary or tertiary datum shall not be specified when it does not constrain more degrees of freedom of the tolerance zone than are constrained by the primary datum and in the case of a tertiary datum also by the secondary datums. Additional examples of datum systems are given in C.3. SIST EN ISO 5459:2011

ISO 5459:2011(E) © ISO 2011 – All rights reserved 15 EXAMPLE 1 Common datum or datum system taken from a cylinder and a plane. Indication of datum feature Indication of datum in tolerance frame Meaning on workpiece Resulting
common datum or datum system
Key 1 first associated feature without orientation constraint 2 second associated feature with orientation constraint from the first associated feature 3 simultaneously associated features with orientation constraint and location constraint 4 maximum distance balanced between the associated features and datum features 5 straight line which is the situation feature of the associated cylinder (its axis) 6 point of intersection between the straight line and the plane NOTE 1 The orientation and location of datums are different depending on the datum indications in the tolerance frame. NOTE 2 The association for datum systems is described in A.2.4.
ISO 5459:2011(E) 16 © ISO 2011 – All rights reserved EXAMPLE 2 Common datum or datum system taken from two cylinders. Indication of datum feature Indication of datums in tolerance frame Meaning on workpiece Resulting
datum or datum system
Key 1 first associated cylinder without constraint 2 second associated cylinder with parallelism constraint from the first associated feature 3 simultaneously associated cylinders with parallelism constraint and location constraint 4 maximum distance balanced between the associated cylinders and datum features 5 straight line which is the axis of the first associated cylinder 6 plane including the axes of the two associated cylinders 7 median straight line of the axes of the two simultaneously associated cylinders NOTE 1 The orientation and location of datums are different depending on the datum indication in the tolerance frame. Not all possibilities for establishing the datums are covered. NOTE 2 For the association method, see Annex A.
ISO 5459:2011(E) © ISO 2011 – All rights reserved 17 EXAMPLE 3 Datum system taken from two cylinders and a plane. Indication of datum feature Indication of datums in tolerance frame Meaning on workpiece Resulting
datum or datum system
Key 1 first associated feature without a constraint 2 second associated feature with a perpendicularity constraint from the first associated feature 3 third associated feature with a perpendicularity constraint from the first associated feature (and parallelism constraint from the second one) 4 plane which is the first associated feature 5 point of intersection between the plane and the axis of the second associated feature 6 straight line which is the intersection between the associated plane and the plane containing the two axes NOTE For the association method, see Annex A.
7 Graphical language 7.1 General The expression of geometrical tolerances with datums in geometrical specifications on drawings includes the following
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