Overview
EN ISO 12780-2:2011 - Geometrical product specifications (GPS) - Straightness - Part 2: Specification operators - defines the complete specification operator for straightness of integral features (features of type line). It specifies how to unambiguously describe the transmission band, probing system and other operators needed to make a straightness specification unique and measurable. The standard complements ISO 12780-1 (vocabulary and parameters) and follows the operator framework of ISO 17450-2.
Key topics and technical requirements
- Complete specification operator: An ordered set of unambiguous specification operations (per ISO 17450-2) that together define the straightness assessment.
- Transmission band / filtering:
- Requires a phase-correct longwave‑pass filter (see ISO 11562) that transmits infinite wavelength and progressively attenuates undulations around the chosen cut-off length.
- Provides an attenuation function and guidance for cut-off selection.
- Includes a table of typical cut-off wavelengths, associated maximum sample point spacing, and maximum stylus tip radius for transmitted undulations.
- Probing system:
- Specifies a contacting probing system with a spherical stylus tip (theoretical geometry).
- Probing force is specified as 0 N to eliminate elastic deformation effects from the specification operator.
- Ambiguity warnings:
- The standard does not set defaults for filter cut-off, probe tip radius or method of association (reference line). If these are not explicitly stated in a specification, the specification is ambiguous and different measurement choices may be used when proving conformance.
- Measurement considerations:
- Addresses aliasing and harmonic content of a nominally straight workpiece (Annex A) and notes Nyquist/sampling implications.
- Refers to ISO 14253-1 for decision rules when proving conformance or non‑conformance.
Applications and who uses it
- Quality and metrology engineers defining straightness specifications for linear features on machined parts, shafts and precision components.
- Calibration and test laboratories developing measurement procedures and traceable reports.
- Manufacturers in precision engineering, automotive, aerospace and machine tool industries implementing consistent straightness verification.
- Metrology equipment manufacturers specifying stylus geometry, sampling resolution and filtering for straightness measurement systems.
Related standards
- ISO 12780-1 - Vocabulary and parameters of straightness
- ISO 11562 - Phase-correct filters for profile filtering
- ISO 14253-1 - Decision rules for proving conformance
- ISO 17450-2 - GPS operators and specification framework
Keywords: EN ISO 12780-2:2011, straightness specification, GPS, specification operators, longwave-pass filter, stylus tip radius, cut-off length, metrology, proving conformance.
