BS EN ISO 5458:2015 pdf download – Geometrical product specifications (GPS) — Geometrical tolerancing — Positional and pattern tolerancing
By default, based on the independency principle defined in ISO 801 5, a geometrical specification of form, orientation, location or run-out, without modifier, applied to n geometrical features (n being greater than one), is equivalent to n independent geometrical specifications: each geometrical feature shall be considered individually and each specification shall be considered individually (independent between them).
The resulting independent tolerance zones correspond to an implicit indication of the SZ (separate zones) modifier: the “all around” modifier does not create itself a united feature or a pattern.
When positional tolerancing is applied to several geometrical features and all the non-redundant degrees of freedoms of the tolerances zones are un-locked, either the SZ (separate zones) modifier or the CZ (combined zone) modifier shall always be indicated in the second compartment of the tolerance indicator.
NOTE This rule allows the potential conflict of interpretation between ISO 1 1 01:2012 and the former ISO 5458:1 998 to be resolved (see Annex B). To create one homogeneous pattern, the modifier CZ shall be indicated in the tolerance section of the tolerance indicator. To create a new level of pattern defined as a homogeneous pattern of more than one homogeneous patterns, an additional CZ modifier shall be indicated after the sequence defining the previous level of pattern.
EXAMPLE One CZ in the tolerance section defines a single pattern. The sequence CZ CZ CZ in the tolerance section defines a pattern of patterns of patterns (pattern of level three).
Between theses tolerance zones:
to manage the orientation constraints and the location constraints, the modifier CZ (combined zone) shall be indicated, and these shall be defined by linear and angular TEDs (implicit or explicit).
to manage the orientation constraints only, the following order of modifiers CZ (combined zone) and “><” (orientation only) shall be indicated, and these orientation constraints shall be defined by angular TEDs (implicit or explicit).
When a geometrical symbol (form, orientation, location (e.g. position), or run-out symbol) is used in the tolerance indicator without indication of a datum, CZ shall be indicated in the second compartment of the tolerance indicator. This rule consolidates the general rules, to use CZ when it is necessary to create a collection of tolerance zones with orientation and location constraints defined between them (see Figure 4 and former practice in Annex A).
When the tolerance zones corresponding to several geometrical specifications indicated separately are not to be considered independently, but with orientation and location constraints defined between them (simultaneous requirement), then the modifier SIM, followed by a number without space if necessary, shall be indicated close to each related geometrical specification, preferably on the free side of the tolerance indicator (see Figures 5 and 9).
NOTE 1 The modifier SIM is not an implicit modifier: see independency principle of ISO 801 5.
NOTE 2 ‘SIM’ in ISO 8785 is used for the Surface IMperfection parameters family with some indices (e.g. a, n, t, w, cd, ch, sh, n/A). The modifier simultaneous requirement (SIM) as indicated in this standard is not to be confused with the indication of an imperfection surface parameter (e.g. SIM1 versus SIMt).
NOTE 3 The free side of the tolerance indicator is the opposite side of the output side in the leader line.
n Figure 5, two specifications create two combined zones which are required to be constrained with location and orientation defined between them (implied by the modifiers SIM1 ). These two specifications do not create two separate requirements: there is only one result for these two specifications, linked with the modifier SIM1 . In Figure 6, two simultaneous requirements are defined (SIM1 and SIM2). Each one considers simultaneously two combined zones respectively composed by:
for SIM1 , two combined zones defining six cylindrical zones (three of diameter 0,1 and three of diameter 0,2) constrained between them in orientation and in location;