prEN ISO 5459
(Main)Geometrical product specifications (GPS) - Geometrical tolerancing - Datums and datum systems (ISO/DIS 5459.2:2017)
Geometrical product specifications (GPS) - Geometrical tolerancing - Datums and datum systems (ISO/DIS 5459.2:2017)
2017-09-20: 2nd enquiry decided to follow ISO
Geometrische Produktspezifikation (GPS) - Geometrische Tolerierung - Bezüge und Bezugssysteme (ISO/DIS 5459.2:2017)
Spécification géométrique des produits (GPS) - Tolérancement géométrique - Références spécifiées et systèmes de références spécifiées (ISO/DIS 5459.2:2017)
Specifikacija geometrijskih veličin izdelka (GPS) - Geometrijsko toleriranje - Reference in sistemi referenc (ISO/DIS 5459.2:2017)
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
01-januar-2018
6SHFLILNDFLMDJHRPHWULMVNLKYHOLþLQL]GHOND *36 *HRPHWULMVNRWROHULUDQMH
5HIHUHQFHLQVLVWHPLUHIHUHQF ,62',6
Geometrical product specifications (GPS) - Geometrical tolerancing - Datums and datum
systems (ISO/DIS 5459.2:2017)
Geometrische Produktspezifikation (GPS) - Geometrische Tolerierung - Bezüge und
Bezugssysteme (ISO/DIS 5459.2:2017)
Spécification géométrique des produits (GPS) - Tolérancement géométrique -
Références spécifiées et systèmes de références spécifiées (ISO/DIS 5459.2:2017)
Ta slovenski standard je istoveten z: prEN ISO 5459
ICS:
17.040.10 Tolerance in ujemi Limits and fits
17.040.40 6SHFLILNDFLMDJHRPHWULMVNLK Geometrical Product
YHOLþLQL]GHOND *36 Specification (GPS)
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
DRAFT INTERNATIONAL STANDARD
ISO/DIS 5459.2
ISO/TC 213 Secretariat: BSI
Voting begins on: Voting terminates on:
2017-11-20 2018-01-15
Geometrical product specifications (GPS) — Geometrical
tolerancing — Datums and datum systems
Spécification géométrique des produits (GPS) — Tolérancement géométrique — Références spécifiées et
systèmes de références spécifiées
ICS: 17.040.10; 01.100.20
THIS DOCUMENT IS A DRAFT CIRCULATED
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ISO/DIS 5459.2:2017(E)
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NOTIFICATION OF ANY RELEVANT PATENT
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PROVIDE SUPPORTING DOCUMENTATION. ISO 2017
ISO/DIS 5459.2:2017(E)
© ISO 2017, Published in Switzerland
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ii © ISO 2017 – All rights reserved
ISO/DIS 5459.2:2017(E)
Contents Page
Foreword . iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols . 7
5 Datum system basics . 10
5.1 Role of datum system . 10
5.2 Concepts . 10
5.2.1 Introduction . 10
5.2.2 Associated feature in link with a datum system . 10
5.2.3 Situation features of associated feature . 11
5.2.4 Datum used to constrain orientation or location of other ideal features . 12
5.2.5 Operations and types of features in the process to establish a datum . 12
5.2.6 Consideration for indication of datum system . 14
6 Datum feature indication . 14
6.1 Datum feature indicator . 14
6.2 Datum feature identifier . 15
6.3 Identification of a single feature as datum feature . 15
6.4 Completeness of datum feature . 17
6.4.1 Generality . 17
6.4.2 Datum features established from a complete feature . 18
6.4.3 Datum features established from a non‐complete feature defined by one or more
datum targets. 18
6.4.4 Datum feature defined as one located restricted feature . 25
6.4.5 Datum feature defined as one unlocated restricted feature . 26
7 Specification of datums and datum systems . 26
7.1 General . 26
7.2 Interdependency to define a partial toleranced feature and partial datum feature . 28
7.3 Datum system indication – Datum section . 29
7.4 Indication of a datum in a datum indicator of a datum section – Datum indicator . 30
7.5 Rules to define associated features from datum features . 31
7.5.1 General . 31
7.5.2 Rule a — Associated feature type . 32
7.5.3 Rule b — Dimension of an associated feature . 34
7.5.4 Rule c — Material constraints for associated feature . 35
7.5.5 Rule d — Constraint between associated features in a common datum . 36
7.5.6 Rule e — Constraint between associated features in a datum system . 36
7.6 Locked or released degrees of freedom for the members of its datum system . 42
7.7 Special indications for common datum . 45
7.8 Identifications of situation feature on technical product documentation . 46
7.9 Degrees of freedom indication in relation with a datum system . 47
7.10 Establishment of a coordinate system from a datum system . 48
ii © ISO 2017 – All rights reserved
ISO/DIS 5459.2:2017(E)
7.11 Application of Ⓜ, Ⓛ and Ⓟ modifiers in a datum indicator . 49
8 Specification operator for datum . 51
8.1 Introduction. 51
8.2 ISO default specification operator for datum . 51
8.2.1 For association . 51
8.2.2 For filtration . 52
8.3 Special specification operator for datum . 53
8.3.1 General . 53
8.3.2 Filtration specification elements for datum . 54
8.3.3 Association specification elements for datum . 55
8.4 Drawing‐specific default for datum . 57
Annex A (informative) Association for datums . 58
Annex B (informative) Invariance classes . 65
Annex C (informative) Indication and meaning of datum systems for some examples . 67
Annex D (normative) Datum feature indicator for threads . 93
Annex E (informative) Examples of a datum system or a common datum established with
contacting features. 95
Annex F (informative) Examples of a datum system established from datum targets . 100
Annex G (informative) Filter symbols and attached nesting index . 105
Annex H (normative) Relations and dimensions of graphical symbols . 106
Annex I (informative) Former practice . 107
Annex J (informative) Relationship to the GPS matrix model . 108
Bibliography . 110
© ISO 2017 – All rights reserved iii
ISO/DIS 5459.2:2017(E)
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.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
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. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following
URL: www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 213, Dimensional and geometrical product
specifications and verification.
This third edition cancels and replaces the second edition (ISO 5459:2011), which has been technically
revised with the following main changes:
the default association criteria has been changed by defining only one independently to the shape
of the nominal integral feature;
the representation and indication to identify the plane, the straight line and the point of a datum
system, have been introduced;
the default filtration method is now defined;
it is allowed to change default filtration and association methods;
it is allowed to define a coordinate system from a datum system.
iv © ISO 2017 – All rights reserved
ISO/DIS 5459.2:2017(E)
Introduction
ISO 5459 is a geometrical product specification (GPS) standard and is to be regarded as a general GPS
standard (see ISO 14638). It influences the chain links A, B and C of the chain of standards on size,
orientation, location, run‐out, profile surface texture and areal surface texture.
The ISO GPS matrix model given in ISO 14638 gives an overview of the ISO GPS system of which this
document is a part. The fundamental rules of ISO GPS given in ISO 8015 apply to this document 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 document to the GPS matrix model, see Annex I.
For the definitive presentation (proportions and dimensions) of symbols for geometrical tolerancing,
see ISO 7083.
This document 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.
Former practice of datums is given in Annex H.
© ISO 2017 – All rights reserved v
DRAFT INTERNATIONAL STANDARD ISO/DIS 5459:2017(E)
Geometrical product specification (GPS) — Geometrical
tolerances — Datum and datum systems
1 Scope
This document specifies terminology, rules and methodology for the indication and understanding of
datums and datum systems in technical product documentation. This document also provides
explanations to assist the user in understanding the concepts involved.
This document defines the specification operator (see ISO 17450‐2) used to establish a datum or a
datum system. The verification operator (see ISO 17450‐2) can take different forms (physically or
mathematically) and is not the subject of this document.
NOTE The detailed rules for maximum and least material requirements for datums are given in ISO 2692.
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 128‐24, Technical drawings — General principles of presentation — Part 24: Lines on mechanical
engineering drawings
ISO 1101, Geometrical product specifications (GPS) — Geometrical tolerancing — Tolerances of form,
orientation, location and run‐out
ISO 2692, Geometrical product specifications (GPS) — Geometrical tolerancing — Maximum material
requirement (MMR), least material requirement (LMR) and reciprocity requirement (RPR)
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
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 1101, ISO 2692, ISO 17450‐1,
ISO 17450‐2 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at http://www.iso.org/obp
— IEC Electropedia: available at http://www.electropedia.org/
ISO/DIS 5459.2:2017(E)
3.1
datum feature
real (non‐ideal) integral feature used for establishing a single datum
Note 1 to entry: A datum feature can be a complete surface, a set of one or more portions of a complete surface, or
a feature of size.
Note 2 to entry: An illustration showing the relations between datum feature, associated feature and datum is
given in Figure 2.
3.2
datum target
specific portion, which is nominally a point, a line segment or an area, taken from a datum feature and
which is totally located on the real workpiece
Note 1 to entry: 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.
3.3
moveable datum target
specific portion, which is nominally a point, a line segment or an area, taken from a datum feature and
which has one freedom of translation along a defined path from other datums established on the real
workpiece
3.4
associated feature (used for datum)
ideal feature which is fitted to the datum feature with a specific association criterion
Note 1 to entry: 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 7.5.2).
Note 2 to entry: The associated feature for establishing a datum simulates by default the contact between the real
surface of the workpiece and other components.
Note 3 to entry: An illustration showing the relations between datum feature, associated feature and datum is
given in Figure 2.
Note 4 to entry: An associated feature may have the same shape as the nominal integral datum feature or it may be
another shape defined as a contacting feature (see 3.22 and Figure 1).
3.5
datum
set of one or more situation features (point, line, plane) issued from one or more associated integral
features
Note 1 to entry: A datum can be used to locate or orientate an ideal feature (e.g. a tolerance zone, an intersection
plane, an orientation plane, a reference feature or an ideal feature representing for instance a virtual condition).
Note 2 to entry: Datums with maximum material condition or least material condition (see ISO 2692) are not
covered in this document.
Note 3 to entry: 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 identifier to limit the situation feature(s) taken into account relative to the surface.
Note 4 to entry: An illustration showing the relation between datum feature, associated feature and datum is given
in Figure 2.
2 ©ISO2017 – All rights reserved
ISO/DIS 5459.2:2017(E)
Note 5 to entry: Without qualifier, a datum is a single datum or a common datum.
3.6
single datum
datum established from one datum feature taken from one single surface or from one feature of size
Note 1 to entry: 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.
Note 2 to entry: See the rule in 7.4.
3.7
common datum
datum established from two or more datum features after simultaneous associations without specific
order and with interrelated constraints
Note 1 to entry: To define a common datum, it is necessary to consider the collected surface created by the
identified datum features. The invariance class of a collected surface can be complex, prismatic, helical, cylindrical,
revolute, planar or spherical (see Table B.1).
Note 2 to entry: See the rule in 7.4.
Note 3 to entry: The result of the common datum cannot be considered as a collection of the situation features of
each associated feature. For example a common datum, established from two parallel non‐coaxial cylinders, is a
set of a plane and a straight line contained in the plane. See Examples 1 to 4 in 7.5.6.
3.8
datum system
set of one or more situation features (point, straight line, plane) resulting from one or more datums
established in a specific order from one or more datum features
Note 1 to entry: To define a datum system, it is necessary to consider the collected surface created by the
identified datum features to identify its invariance class (see Table B.1).
Note 2 to entry: A datum system can consist of one common datum or one single datum.
Note 3 to entry: The role of a datum system is described in 5.1.
3.9
datum section
specification element containing one, two or three datum indicators
Note 1 to entry: A datum section can be used as a part of a tolerance indicator, an intersection plane indicator, an
orientation plane indicator, collection plane indicator or a direction feature indicator (see ISO 1101). See Figure 2.
3.10
datum indicator
specification element containing only one datum identifier
Note 1 to entry: See Figure 2.
3.11
datum identifier
label, designating a datum in a datum indicator, which is identical to the datum feature identifier in the
case of a single datum, or which is a sequence of datum feature identifiers separated by an hyphen in
the case of a common datum
© ISO 2017 – All rights reserved 3
ISO/DIS 5459.2:2017(E)
Note 1 to entry: See Figure 2.
3.12
situation feature identifier
label, designating a situation feature (point, straight line or plane) related to a datum
3.13
datum feature identifier
label, defined by one or more capital letters, identifying the nominal integral feature, corresponding to a
datum feature
Note 1 to entry: The same label is also used to identify a single datum.
Note 2 to entry: see Table 1 and Clause 6.
3.14
datum feature indicator
graphical symbol used to define an integral feature as a datum feature and containing a datum feature
identifier
Note 1 to entry: See Table 1 and 5.2.
3.15
primary datum
datum indicated in the first datum indicator of the datum section
Note 1 to entry: A primary datum is not influenced by constraints from other datums (see 7.1).
3.16
secondary datum
datum indicated in the second datum indicator of the datum section
Note 1 to entry: A secondary datum is constrained at least in orientation from the primary datum (see 7.1).
3.17
tertiary datum
datum indicated in the third datum indicator of the datum section
Note 1 to entry: The tertiary datum is constrained at least in orientation from the primary datum and the
secondary datum (see 7.1).
3.18
collected surface
two or more surfaces considered simultaneously as a surface
Note 1 to entry: Table B.1 is used to determine the invariance class of datums or datum systems when using a
collection of surfaces.
Note 2 to entry: Two intersecting planes may be considered simultaneously or sequentially (one after the other).
When the two intersecting planes are considered simultaneously as a single surface, that surface is a collected
surface.
3.19
objective function
objective function for association
formula that describes the goal of association
Note 1 to entry: In this document, the term "objective function" refers to "objective function for association".
4 ©ISO2017 – All rights reserved
ISO/DIS 5459.2:2017(E)
Note 2 to entry: The objective functions are usually named and mathematically described: maximum inscribed,
minimum zone, etc.
3.20
(association) constraint
requirement to establish an associated feature
EXAMPLE Orientation constraint, location constraint, material constraint or intrinsic characteristic
constraint.
3.20.1
orientation constraint
constraint on one or more rotational degrees of freedom between the situation features of associated
feature
3.20.2
location constraint
constraint on one or more translational degrees of freedom between the situation features of associated
feature
3.20.3
material constraint
additional condition to the location of the associated feature, relative to the material of the feature,
while optimizing an objective function
Note 1 to entry: 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.
3.20.4
intrinsic characteristic constraint
additional requirement applied to the intrinsic characteristic of an associated feature whether it is
considered as fixed or variable
3.21
association criterion
objective function with or without constraints, defined for an association
Note 1 to entry: Several constraints may be defined for an association.
Note 2 to entry: Association results (associated features) may differ, depending upon the choice of association
criterion.
Note 3 to entry: Default association criteria are defined in 8.2.
3.22
contacting feature
ideal feature, with theoretical exact geometry (shape and dimension), different from the nominal
geometry of the integral geometrical feature with which it is in contact
Note 1 to entry: A contacting feature can be used to define a set of one or more datum features, and/or to establish
a datum.
Note 2 to entry: See rule a in 7.5.2.
Note 3 to entry: See Figure 1.
© ISO 2017 – All rights reserved 5
ISO/DIS 5459.2:2017(E)
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
3.23
datum coordinate system
cartesian coordinate system established from a datum system
Note 1 to entry: The datum coordinate system can describe some degrees of freedoms, which are locked through
the datum system.
Note 2 to entry: Using a datum coordinate system is optional.
EXAMPLE A datum system defined by only a primary datum, which is a plane, can allow establishing a
non‐unique datum coordinate system, one translation and two rotations being locked by the primary datum.
6 ©ISO2017 – All rights reserved
ISO/DIS 5459.2:2017(E)
Key
datum section
datum indicator
datum identifier
datum feature indicator
datum feature identifier
datum target indicator
Cartesian system identicator
Figure 2 — Identification of specification elements attached to the descriptioin of a datum
system
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 with the datum identifier.
© ISO 2017 – All rights reserved 7
ISO/DIS 5459.2:2017(E)
Table 1 — Datum features and datum target symbols and indications
Description Indication /Symbol Subclause
Datum feature indicator 6.1
Datum feature identifier Capital letter (A, B, C, AA, etc.) 6.2
Single datum target
6.4.3.2.2
indicator
Moveable datum target
6.4.3.2.3
indicator
Datum target point 6.4.3.2.4
Closed datum target line 6.4.3.2.4
Open datum target line 6.4.3.2.4
Datum target area 6.4.3.2.4
Datum coordinate system 7.9
3D representation 2D representation
Between symbol
Restricted datum feature 6.4.4
Contacting feature 7.5.2
Indication of a situation
feature of a datum, which is 7.6, 7.7, 7.8
a plane
8 ©ISO2017 – All rights reserved
ISO/DIS 5459.2:2017(E)
Table 2 — Modifier symbols
Symbol Description Available for Subclause
PD Pitch diameter 6.3
MD Major diameter 6.3
Datum feature
LD Minor diameter 6.3
and toleranced
ACS Any cross section 7.2
feature
ALS Any longitudinal section 7.2
Projected (for secondary or tertiary datum) 7.11
Least material requirement Associated See ISO 2692
feature and
toleranced
Maximum material requirement See ISO 2692
feature
[CF] Contacting feature 7.5.2
[SF] Fixed size 7.5.3
[SV] Variable size 7.5.3
Associated
[DV] Variable distance (for common datum) 7.5.5
feature
[DF] Fixed distance 7.5.6
Datum used for orientation constraint only
[ ] 7.6
to establish the following datum
[PT] (situation feature of type) point 7.6, 7.7
[SL] (situation feature of type) straight line 7.6, 7.7
[PL] (situation feature of type) plane 7.6, 7.7
Datum used for orientation constraint of the Tolerance zone,
tolerance zone, intersection plane, and other
7.6
orientation plane, direction feature or specification
collection plane feature
a
Ti Translation along direction i (e.g Tx) 7.6
a
Ri Rotation around direction i (e.g Rz) 7.6
[CSi] Datum coordinate system identifier N°i 7.9
[DSi] Datum sytem identifier N°i Datum system 7.3
a
Direction corresponding to an axis labels of the datum coordinate system, x, y or z.
© ISO 2017 – All rights reserved 9
ISO/DIS 5459.2:2017(E)
5 Datum system basics
5.1 Role of datum system
A datum system allows considering orientation and/or location constraints to establish a tolerance
zone, an intersection plane, an orientation plane, a direction feature or a collection plane.
A datum system can be seen as a means to lock a set of one or more degrees of freedom of an ideal
feature (e.g. a tolerance zone). For example, in the case of the tolerance zone, the number of degrees of
freedom which are locked depends on the invariance class in link with the datum system and on the
toleranced characteristic indicated in the geometrical tolerance indicator.
A datum system can serve to establish a datum coordinate system in relation to a real workpiece (see
7.10). When the datum system does not lock all degrees of freedom, then the datum coordinate system
cannot be completely defined.
NOTE 1 A datum system can be defined when all information related to it is specified (see Clause 6): e.g.
indication of datum system, indication of datum features and their completeness.
NOTE 2 The functional stability of a datum system depends on the extent of datum features from which it is
defined.
NOTE 3 Datums and datum systems are not coordinate systems. Coordinate systems can be built from datum
systems.
5.2 Concepts
5.2.1 Introduction
A datum system consists of a set of one or more situation features consisting in one of the following set:
a plan, a straight line (included in the plane) and a point (included in the straight line); or
a plan and a straight line (included in the plane); or
a straight line and a point (included in the straight line); or
a plan; or
a straight line; or
a point.
The concept of situation features is inherently reliant upon the invariance class concept (see Annexes A
and B).
This set of point, straight line and plane are the situation features of one or more associated features
(feature of perfect form) which are established from the identified real surfaces of the workpieces
called datum features (extracted integral features). A datum features may be complete features, or
identified portions thereof (see Clause 6).
5.2.2 Associated feature in link with a datum system
Associated features are established from datum features, which are extracted integral single features.
10 ©ISO2017 – All rights reserved
ISO/DIS 5459.2:2017(E)
The associated feature can be defined by an operation of association including constraints from the
extracted integral feature itself or from one or more preceding associated features. The situation
features, which define the datum, are determined from these associated features. The default
association methods are given in 8.2 and special association method can be defined: see 8.3. The default
association has been chosen to simulate the contact between the real surface of the workpiece and
other components considered as perfect.
The associations with one or more datum features can be performed:
directly, from one datum feature, in case of a single datum;
simultaneously, from more than one datum features (case of common datum):
with orientation constraints and location constraints, between associated features; or
with orientation constraints only, between associated features;
sequentially, from more than one datum features defined by a set of a single or a common datum,
one association after one other:
with orientation constraints from the previous associated features; or
with orientation constraints and location constraints from the previous associated features.
The association process (see rule a to rule e in 7.5.2 to 7.5.6) shall consider an objective function (e.g.
least square, Chebitchev) and the following constraints:
from each datum feature
material constraints (outside, inside, medium none, shifting outside, shifting inside),
size constraints (intrinsic characteristic considered as fixed or variable),
between associated features
orientation constraints,
location constraints.
5.2.3 Situation features of associated feature
All single or collected integral ideal features belong to one of the following invariance classes which give
a correspondence with a set of one or more situation features (see Annex B).
NOTE Some geometrical features are considered by simplification as belonging to a cylindrical invariance
class, e.g. gear and thread (see Annex D).
To establish the situation features related to:
a single datum, it is necessary to identify the invariance class of the associated feature established
from its datum feature;
a common datum, it is necessary to identify the invariance class of the collection of associated
features established from their datum features;
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a datum system, it is necessary to identify the invariance class of the collection of associated
features established from the set of datum features.
EXAMPLE A single datum taken from a cone has two situation features: its axis and a point on that axis.
When the associated feature has more than one situation feature, then it is possible to exclude some of
the situation features by selecting the desired ones from the set, see rule in 7.6.
5.2.4 Datum used to constrain orientation or location of other ideal features
A datum system locks by default all the degrees of freedom (reference feature of the tolerance zone,
intersection plane, orientation plane, …) that it can lock in accordance with:
the specification elements (geometrical symbol indicated in the tolerance indicator, intersection
plane, orientation plane, direction feature, …); see examples 1 and 2 hereafter;
the invariance class of the collection feature constituted by the set of one or more nominal integral
features corresponding to the datum features from which the datum system is established.
EXAMPLE 1 In an angularity specification, the tolerance zone is only constrained in orientation from the
datum system, defined from the indication of the datum section (angularity symbol imposes only angular
constraints). These orientation constraint values are indicated by using one or more angular theoretically exact
dimension (TED angle : implicit or explicit)
EXAMPLE 2 In a position specification, the tolerance zone is constrained in orientation and in location from
the datum system defined from the indication of the datum section (position symbol imposes both angular and
distance constraints). These constraint values (location and orientation) are indicated by using one or more
theoretically exact dimension (angular and linear TED, implicit or explicit).
It is possible to unlock one or more degrees of freedom, by using complementary indications or
modifiers (see 7.6).
5.2.5 Operations and types of features in the process to establish a datum
Figure 3 illustrates and identifies the different types of features used in the process to establish a
datum, in the case datum system is defined as a single datum.
In the example given in Figure 3, the nominal shape of the datum feature is a cylinder. To establish the
datum from the real surface corresponding to this nominal feature, the following sequence of
operations is performed:
partition to define the real integral surface corresponding to the nominal feature, see Figure 3 a);
extraction to provide the extracted integral feature, see Figure 3 b);
filtration (see 8.2.2 and 8.3.2);
association (see 8.2.1 and 8.3.3) to provide the associated feature, see Figure 3 c).
The datum is defined as the situation feature (the axis) of the associated cylinder; see Figure 3 d).
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ISO/DIS 5459.2:2017(E)
a) Integral real surface of b) Extraction
the workpiece
c) Association d) Datum
Key
1 real integral feature (datum feature in this case)
2 extracted integral feature (optional)
3 associated integral feature
4 derived feature of associated integral feature
5 single datum (situation feature of the associated feature)
In the example shown in Figure 3, the derived feature (key 4) and the situation feature (key 5) are
identical. This is often not the case.
Figure 3 — Illustration of features used for establishing a single datum from a cylinder
The expression of specification elements with datums on drawings shall include the following steps.
Indicate the integral surfaces of the workpiece which are to be used as datum features.
When a complete integral surface is not required for a datum feature, the considered portion(s)
called datum target(s) [area(s), line(s) or point(s)] and the corresponding dimensions and
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locations shall be indicated. When these portions are lines or points, then it is necessary to
define the geometry of the contacting feature or the used intersection plane allowing the
definition of the datum target on the real workpiece.
Indicate the datum system in the datum section, by one or more datum indicators which shall take
into account the intended constraints and the association criteria. The default association criteria
are defined in 8.2. If a different association criterion is required, it shall be indicated. Indicate in
datum indicator where necessary, the use of the maximum or least material requirement (see
ISO 2692) or projected datum.
5.2.6 Consideration for indication of datum system
The expression of specification elements with datum system on drawings shall include the following
steps.
Indicate the integral surfaces of the workpiece which are to be used as datum features (see
Clause 6).
When a complete integral surface is not required for a datum feature, the considered portion(s)
called datum target(s) [area(s), line(s) or point(s)] and the corresponding dimensions and
locations shall be indicated. When these portions are lines or points, then it is necessary to
define the geometry of the contacting feature or the used intersection plane allowing the
definition of the datum target on the real workpiece
Indicate the datum system in the datum section (see Clause 7), by one or more datum indicators
which shall take into account the intended constraints and the association criteria. The default
association criteria are defined in 8.2. If a different association criterion is required, it shall be
indicated. Indicate in datum indicator where necessary, the use of the maximum or least material
requirement (see ISO 2692) or projected datum.
6 Datum feature indication
6.1 Datum feature indicator
Single nominal integral features to be used for establishing datum features shall be indicated by a
datum feature indicator.
The datum features indicator is a rectangular compartment, in which datum feature identifier is
defined, and which is connected to a leader line terminating in a filled or open triangle, such as the base
of the rectangle should be orientated for reading from the bottom of the drawing, see Figure 4.
NOTE There is no difference in meaning between a filled and an open datum triangle.
Figure 4 — Basic graphical symbols for datum feature indicator, without its identifier
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ISO/DIS 5459.2:2017(E)
6.2 Datum feature identifier
Single integral features used for establishing datum features shall be identified by a datum featur
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