Developments in Australia's surface roughness measurement system

Abstract

Roughness standards in Australia are established, maintained and disseminated by the Melbourne Branch of the National Measurement Laboratory (NML), Commonwealth Scientific and Industrial Research Organisation (CSIRO). A Taylor Hobson Talysurf 3 stylus instrument has been upgraded by replacement of the original valve amplification with solid-state electronics and the implementation of Windows 95 based software for profile analysis. The amplification is calibrated using gauge blocks wrung onto an optical flat or with master groove standards, calibrated using an interference microscope with a helium–neon laser light source. Measurements of step height or peak-to-valley roughness height in the range 0.1–50 μm are possible. The stylus instrument interfaces directly with a PC via a high speed analogue-to-digital card. Software has been developed to analyse grooves and steps and to characterise surfaces by calculation of various parameters such as arithmetic mean deviation ( R a). Typical uncertainties are better than 4% at a confidence level of 95% and are calculated automatically by the software according to the ISO “ Guide to the Expression of Uncertainty in Measurement”. Technical and administrative procedures are discussed in the context of accreditation within the National Association of Testing Authorities, the Australian laboratory accreditation organisation. The facility has participated informally in a regional Asia–Pacific Metrology Programme intercomparison in which three surface roughness and two groove standards were circulated and the results are discussed. Using historical data, alternate traceability routes, and various artefact chains, the integrity of surface texture measurement at the new facility has been evaluated and verified.