Relation of Surface-Roughness Readings to Actual Surface Profile

Abstract Studies of surface finish have shown the desirability of relating profilometer roughness readings to actual peak-to-valley distances of the type that a micrometer measures. Approximate multiplying factors for converting profilometer readings into peak-to-valley roughness have been obtained from taper sections of a variety of abrasive-finished steel surfaces with profilometer roughness in the range of 1 to 100 microinches rms. For cylindrical ground surfaces, the factor can be taken as about 4½; for other types of fixed-abrasive finishes, as 6 or 7; and for loose-abrasive-lapped surfaces, as 10. These are mean values and individual factors may deviate by as much as one third of the mean value. The factors quoted give values for “predominant peak” roughness; they should be doubled to obtain “deepest maximum” roughness, this being a second way of describing the peak-to-valley roughness. No evidence was found of any increase in the factor for a given type of finish with a decrease in the profilometer roughness, even for the finest surfaces studied.