BS EN ISO 21920-3-2022 pdf free download.Geometrical product specifications (GPS) — Surface texture: Profile Part 3: Specification operators
4 Complete specification operator
4.1 Introduction For non-explicitly specified specification elements (see ISO 21920-1) and often-used specification operators, default settings are used. Default settings should not be expected to ensure correlation with any particular workpiece function. The advantage of the default specification operators given in 4.3 and 4.4 is to simplify the drawing indications.
4.2 General The complete specification operator (see ISO 17450-2) consists of all the operators required for an unambiguous specification. It consists of an ordered full set of unambiguous specification operations in an unambiguous order. For profile surface texture, the complete specification operator defines all setting elements.
The basis for the default settings is the drawing indication according to ISO 21920-1. For R-parameters either the setting class or the profile L-filter nesting index shall be specified. For W-parameters either the setting class or the profile S-filter nesting index shall be specified. For the R-parameters Ra, Rq, Rz, Rp, Rv, Rzx and Rt, and for Pt, all default settings can be specified by the specification of the tolerance limit, see 4.4.3 to 4.4.6.
A flowchart illustrating the general way to determine the specification operators is given in Annex A. Examples for the determination of default settings are given in Annex B. Annex C provides an overview of the most important changes in the determination of the default settings according to this document in relation to ISO 4288. A recommendation for the selection of settings in the absence of a specification is given in Annex D. Annex E provides an overview of the profile and areal standards in the GPS matrix model.
NOTE 1 There is no distinction between periodic and non-periodic profiles.
NOTE 2 This document describes specification operators. For the verification, the following applies: “the verification operator is the physical implementation of the specification operator. It may have exactly the same operations in the same order, in which case the method uncertainty is zero, or it may have different operations or perform the operations in a different order, in which case the method uncertainty is not zero.” [SOURCE: ISO 8015:2011, 5.10.1]
NOTE 3 There are no defaults for electromagnetic profiles.
4.3 General default settings When specifying surface texture by the profile method, the surface is the toleranced feature.
Therefore, the profile direction and the profile position are an integral part of the specification. Surface imperfections and surface defects are part of the specified surface and shall be taken into account when determining profile locations, if not otherwise stated. The general default settings given in Table 1, independent of the specified parameter type, shall be implemented.
NOTE Considering surface imperfections and surface defects as part of the specified surface is a change from ISO 4288.
4.4 Default settings based on the specification
4.4.1 General rules
This subclause defines rules for the default settings based on the specification in addition to the general default settings.
If several parameters are specified within one graphical symbol, the parameter in the first line shall be used to select the default settings.
If more than one specification element is specified, the topmost specification element shall be used to define the column for all non-explicitly specified default settings in Tables 2 to 6.
If a nesting index N ic not listed in Tables 2 to 6 is specified, a second specification element shall be specified, for example the setting class Scn, to define the column for all other non-explicitly specified settings.
If a nesting index N is not listed in Tables 2 to 6 is specified, the maximum sampling distance d x shall be N is /5, for example if N is = 5 µm then the maximum sampling distance d x = 1 µm.
If there is a contradiction between the default profile direction and the default measuring length, the rofile direction shall be respected first.
NOTE See examples in B.1 to B.8.
4.4.2 Default settings based on N ic or Scn
For all R-parameters, except for Ra, Rq, Rz, Rp, Rv, Rzx and Rt, one of the following specifications shall be given in the drawing indication:
— the profile L-filter nesting index N ic ; or
— the setting class Scn.
For all W-parameters one of the following specifications shall be given in the drawing indication:
— the profile S-filter nesting index N ic ; or
— the setting class Scn.
For all P-parameters, except for Pt, one of the following specifications shall be given in the drawing indication:
— the profile S-filter nesting index N is ; or
— the setting class Scn.
This defines the default settings according to the corresponding column in Table 2, which defines the non-explicitly specified settings.BS EN ISO 21920-3 pdf download.