Surface Finish, and How It Can Be Measured and Specified

THIS paper deals with surface finish from the standpoint of the size and shape of the irregularities which constitute the surface. Profiles of a number of common surfaces have been recorded with an instrument called the Profilograph, and these records can be read directly in inch units.

Various machining and finishing operations vary widely, not only in the size of the irregularities, but also in the shape. From this it appears that a single number is not a sufficient specification for a finish when different types of operation are to be compared.

Profilograms of several surfaces are shown, and a brief description given of the advantages and disadvantages of several methods which have been suggested for measuring finish.