ISO 5458:1998 pdf download – Geometrical Product Specifications (GPS) – Geometrical tolerancing – Positional tolerancing

03-05-2022 comment

ISO 5458:1998 pdf download – Geometrical Product Specifications (GPS) – Geometrical tolerancing – Positional tolerancing
1 Scope
This International Standard describes positional tolerancing. This tolerancing method is applied to the location of a point, of a line nominally straight and of a surface nominally plane, e.g. the centre of a sphere, the axis of a hole or shaft and the median surface of a slot.
NOTE Profile tolerancing is used when lines are not intended to be straight or surfaces are not intended to lie in a plane; see ISO 1 660.
2 Normative reference
The following standard contains provisions which, through reference in this text, constitute provisions of this International Standard. At the time of publication, the edition indicated was valid. All standards are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent edition of the standard indicated below. Members of IEC and ISO maintain registers of currently valid International Standards.
ISO 1 1 01 :— 1 ) , Geometrical Product Specifications (GPS) — Geometrical tolerancing — Generalities, definitions,symbols, indication on drawings.
3 Definitions
Definitions related to features are under development and will be issued as ISO 1 4660-1 . This work will result in new terms that are different from those used in this International Standard. These new terms are defined in annex A and appear in the main body of this International Standard in parentheses next to the currently used term .
4 Establishment of positional tolerances
4.1 General
The primary constituents are theoretically exact dimensions, tolerance zones and datums.
4.2 Fundamental requirement
Positional tolerances are associated with theoretically exact dimensions and define the limits for the location of actual (extracted) features, such as points, axes, median surfaces, nominally straight lines and nominally plane surfaces relative to each other or in relation to one or more datums. The tolerance zone is symmetrically disposed about the theoretically exact location.
NOTE Positional tolerances do not accumulate when theoretically exact dimensions are arranged in a chain (see figure 4).(This contrasts with dimensional tolerances that are arranged in a chain.) Positional tolerancing allows clear reference to be made to one or more datums.
4.3 Theoretically exact dimensions
Theoretically exact dimensions, both angular and linear, are indicated by being enclosed in a rectangular frame in accordance with ISO 1 1 01 . This is illustrated in figures 2 a), 2 b), 3 a), 4 a), 5 a) and 7 a).
The theoretically exact dimensions 0° and 90°, 1 80° or distance 0 between
– positionally toleranced features not related to a datum [see figure 4 a) and figure 5 a)],
– positionally toleranced features related to the same datum(s) [see figure 2 a)],
– positionally toleranced features and their related datums (see figure 1 ),
are implied without specific indication.
When the positional tolerance features share the same centreline or axis they are regarded as theoretically exactly related features, unless otherwise specified, e.g. in relation to different datums or other reason indicated by an appropriate note on the drawing as shown in figure 2 b).

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