Importance of checking the stylus radius in the measurement of surface roughness

Abstract All national and international standards on the assessment of surface roughness are based on the profile of a surface traced by a suitable stylus. The accuracy of this measurement and its numerical evaluation for determining the surface parameters depend on the fidelity of the representation of the trace to the cross-sectional profile of the part. However, for a perfect reproduction of the traced surface, the stylus tip radius should be as small as possible. Different styli or worn styli present different results. The difference lies in the determination of the trajectory drawn through the surface profile, to which the surface roughness height is referred. The extent of this difference due to a worn stylus is not known. In this paper results obtained using two different styli are compared: one is up to the standard and the second deviates slightly from it. Comparison between the results is included, confirming the existence of a large discrepancy between the two cases.