6 - Surface Finish Specification

Abstract

This chapter focuses on the specification of a surface finish (SF) and its texture. SFs are of the order of tens of microns and are the machining marks caused by a combination of the tool shapes and the feeds across a workpiece. In many instances, SFs and textures may have significant influences on functional performance. The SF is normally measured by a stylus, which is drawn across the surface to be measured. The stylus moves in a straight line over the surface driven by a traversing unit. The most common method of assessing a SF is by traversing a stylus across a surface. International Standards Organization (ISO) 3274:1996 provides styli in a standard range of spherical radii of 2, 5, and 10 um and includes cone angles of 60° and 90°. In case of a flat surface, the traverse unit drives the stylus over a distance called “the evaluation length (EL).” This length is divided into five equal parts, each of which is called “a sampling length (SL).” ISO 4287:1997 defines the sample length as the length in the direction of the X-axis used for identifying the irregularities characterizing the profile under evaluation.