ISO 12181-2:2011

Overview

ISO 12181-2:2011 - Geometrical product specifications (GPS) - Roundness - Part 2: Specification operators - defines the complete specification operator for roundness assessments of integral, circular features only (complete roundness profiles). It prescribes how to unambiguously specify the transmission band, probing system and stylus geometry used to evaluate roundness so that results are comparable and suitable for conformity decisions.

Key topics and technical requirements

• Complete specification operator: An ordered, unambiguous set of specification operations (per ISO 17450-2) that together define how roundness is assessed (transmission band, probe geometry, etc.).
• Transmission band (filters):
  • Longwave-pass filter: Phase-correct (per ISO 11562), transmits from 1 UPR (undulation per revolution) and attenuates around the cut-off frequency. Common cut-offs shown include 15, 50, 150, 500, 1500 UPR.
  • Shortwave-pass filter: Phase-correct, transmits undulations shorter than the cut-off. If a shortwave-pass filter is used, a longwave-pass must also be specified to form a defined band.
  • Attenuation behavior: Defined attenuation functions determine how sine-wave components are reduced by filters.
• Limiting UPR, sampling and stylus requirements:
  • Table of limiting values gives recommended minimum sample counts and minimum diameter-to-tip‑radius (d:r) ratios for various longwave cut-offs (e.g., higher cut-offs require many more samples and larger d:r to avoid tip-induced distortion).
  • If the d:r ratio is too low, high‑UPR undulations can be distorted by the stylus tip.
• Probing system:
  • Contact stylus probe with a spherical tip is part of the operator.
  • Probing force specified as 0 N to exclude elastic deformation effects from the specification.
• Data extraction and aliasing:
  • Sampling must satisfy Nyquist considerations to avoid aliasing; the standard discusses harmonic content and sampling recommendations.
• Specification completeness:
  • ISO 12181-2 does not set defaults for filter UPR, probe tip radius or method of association (reference circle). These must be explicitly stated in specifications; otherwise the specification is ambiguous.
• Conformance rules: Use ISO 14253-1 decision rules for proving conformance.

Applications and users

• Used by:
  • Metrology labs, quality engineers and inspection teams verifying circular features (bearings, shafts, bores, journal surfaces).
  • Manufacturers of precision rotating components, machine-tool builders and CMM/software vendors.
• Practical uses:
  • Defining unambiguous roundness specifications on drawings and QA documentation.
  • Setting measurement procedures for stylus-based roundness instruments and data-analysis software.
  • Ensuring repeatable, comparable roundness results across suppliers and inspection systems.

Related standards

• ISO 12181-1:2011 - Vocabulary and parameters of roundness
• ISO 17450-2:2011 - GPS concepts, operators and uncertainties
• ISO 11562:1996 - Phase-correct filters (surface texture)
• ISO 14253-1:1998 - Decision rules for proving conformance

Keywords: ISO 12181-2, roundness specification, GPS, UPR, longwave-pass filter, shortwave-pass filter, stylus tip, d:r ratio, Nyquist, aliasing, roundness measurement.