Measuring Surface Finish

In the past surface texture has been assessed by the judgment of the inspector either by eye or even fingernail. The evaluation was done by comparing the surface to be measured with standard surfaces

A modern typical surface measuring instrument will consist of a stylus with a small tip (diamond) a gauge or transducer, a traverse datum and a processor. The surface is measured by moving the stylus across the surface. As the stylus moves up and down along the surface, the transducer converts this movement into a signal which is then exported to a processor which converts this into a number and usually a visual profile.

The stylus must be moved in a straight line to give accurate readings On an expensive fixed instrument the necessary guide is of some form of datum bar that is usually lapped or precision ground to a high straightness tolerance. On the normal portable units the guide is generally based on a skid which slides over the general surface ensuring that the linked stylus moves in a straight line parallel to the local surface.