BS EN ISO 5458-2015 pdf download.Geometrical Product Specifications (GPS) – Geometrical tolerancing一Positional and pattern tolerancing.
5 Principles
5.1 General
In order to manage functional needs, the toleranced feature can be identifiedy as:
a single feature: complete or restricted;
a pattern: homogeneous or non-homogeneous.
This International Standard deals only with a pattern.
This same functional need can be applied to several toleranced features, considered independently to each
other or with constraint between them.
This pattern (homogeneous or non-homogeneous) can be constrained in orientation or in location from a datum system.
There is no functional difference in using or not using the concept of pattern when the specifications managing the patterns (composed by n geometrical features) use a datum system which locks all degrees of freedom of the related tolerance zones. However, when the concept of pattern is used there is only one result of measurement, and when the concept of pattern is not used there are n results of measurement.
There is a functional difference in using or not using the concept of pattern when the specifications managing the patterns (composed by n geometrical features) use a datum system which does not lock all degrees of freedom of the related tolerance zones.
The rules, applied for repetition or pattern, are presented in 5.2 and examples with their meanings are given in Annex C.
5.2 Rules
To create a specification on a homogeneous pattern, it is necessary to indicate that a geometrical specification applies to a repetition of geometrical features.
To create a requirement on a non-homogeneous pattern, it is necessary to indicate that a set of more than one geometrical specification is applied simultaneously.
The rules A to F allow expressing requirements on homogeneous and non-homogeneous pattern and their repetition.
Rule A: Indication of repetition of application of the same specification
It is possible to indicate a repetition as described in ISO 1101, in different ways:
a) directly by using several leader lines coming from an unique tolerance indicator or by using an pall around” symbol (see Figure 1):
b) indirectly by using:
1) nx above the tolerance indicator (see Figure 2) when no interpretation is possible for the identification of nmembers;
2) nx above the tolerance indicator followed by an identifier letter (see Figure 3) when an interpretation is possible for the identification of n members of a pattern on the workpiece. The identifier letter shall be also indicated individually to identify each member with a leader line with a terminator (arrow or dot).BS EN ISO 5458 pdf download.