Overview
EN ISO 12181-1:2011 - Geometrical product specifications (GPS) - Roundness - Part 1: Vocabulary and parameters of roundness - defines the terminology, concepts and basic parameters used to describe and specify roundness of individual integral features. It covers complete roundness profiles only and provides the vocabulary and parameter definitions needed to specify, measure and report roundness in a GPS-compliant way.
Key topics
- Scope and purpose
- Defines terms and concepts related to roundness of individual integral features (cylindrical surfaces or surfaces of revolution).
- Applies to complete extracted roundness profiles and their filtered representations.
- Profiles and extraction
- Extracted circumferential line: digital representation of the intersection of the real surface and a roundness plane.
- Roundness profile: extracted line after an applied filter (mean-line or other).
- Reference circles and centres
- Minimum zone (MZ): pair of concentric circles with least radial separation (outer/inner/mean).
- Least squares (LS): circle minimizing sum of squared deviations.
- Minimum circumscribed (MC) and maximum inscribed (MI) reference circles.
- Associated derived centre: centre of the chosen reference circle(s).
- Filter and spectral concepts
- Wave filter, undulation cut-off, transmission band and undulations per revolution (UPR) - filter characteristics strongly affect the roundness definition and must be specified.
- Parameters
- Peak-to-valley roundness deviation (defined for all reference circles).
- Peak-to-reference roundness deviation (defined for least squares reference).
- Additional parameter definitions and mathematical formulations are included (see annexes).
- Annexes
- Mathematical definitions of roundness tolerances, synoptic tables of terms, and relation to the GPS matrix model.
Applications and who uses it
- Metrology and measurement labs establishing roundness measurement procedures.
- Design and quality engineers specifying form tolerances for rotating parts (shafts, bearings, seals).
- Manufacturing and inspection teams in automotive, aerospace, bearing, precision engineering and machine tool industries.
- Developers and users of roundness measuring instruments and software (CMMs, form testers) to ensure consistent filtering, reference selection and parameter reporting.
- Standards writers and auditors ensuring GPS-compliant specification and verification.
Practical value
- Provides a common vocabulary for unambiguous specification and communication of roundness requirements.
- Ensures consistent interpretation of measured roundness through defined reference circles and filter rules.
- Supports reliable tolerance verification, interchangeability and functional assessment of circular features.
Related standards
Keywords: EN ISO 12181-1:2011, roundness, GPS, roundness parameters, reference circle, roundness profile, UPR, peak-to-valley.