Paper 30: Review of Surface Texture Measurement and the Associated Metrological Problems

Abstract

A brief review is presented of the physical phenomena (optical, capacitance, conductance, absorption, pneumatic, and hydraulic) which have been utilized in the various types of instruments developed to express, by means of a single index, the relative roughness of different specimens. The readings taken with such instruments are normally functions of the three-dimensional characteristics of the surface under test but, since they are of an empirical nature, there is little or no correlation between measurements made with the different types of instruments. Instruments measuring in two dimensions and recording in absolute units of length have been universally accepted. The most popular instrument is the stylus tracer type with electronic amplification of the stylus movement. The output of these devices is dependent on factors that have been standardized by the manufacturers (electronic circuitry, the form of stylus, etc.) and other elements, the characteristics of which are not uniform for all instruments (stylus support and mounting, etc.). Reference is made to the basic datum to which the readings of tracer instruments refer, the envelope line and the centre line, and the different parameters currently advocated as presenting an adequate means of describing and forming a quantitative assessment of the surface under test. The use of digital computer techniques for eliminating the many analogue devices necessary for the evaluation of the different parameters is explained.