Specification And Control Of Surface Finish: Empiricism Versus Dogmatism

This paper reviews the development of the analysis of surface finish from the early attempts in the 1930s to the present day. The development of parameters used in surface analysis is shown in context with the instrumental techniques available at the time, and it is argued that characterization based on graphical and experimental convenience has influenced industrial practice. As the requirements of manufacture and functional performance have been stretched by advancing technology, many industrialists have been forced to accept the fact that existing specification practices are limited and have sought alternative descriptions based on well-established techniques; but these techniques themselves are limited, their suitability to in-process measurement being practically nonexistent. It is shown that attempts have been made recently to develop optical methods of assessing surface finish using traditional parameters such as Ra. This paper suggests that it may be time to look toward a new form of specification that is more suited to assessment by optical transducers, and some methods of assessment are proposed. To support this view, a simple low-cost device is discussed that can be calibrated to give Ra but that also presents information in a more relevant empirical way that may be more valid than the existing parameter specification.