How do we measure surface texture?

In the past surface texture has been assessed by the judgement of the inspector either by eye or even fingernail. In order to put a number to the surface texture, we need to use a more accurate means of measurement. A typical surface measuring instrument will consist of a stylus with a small tip (fingernail), 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.

For correct data collection, the gauge needs to pass over the surface in a straight line such that only the stylus tip follows the surface under test. This is done using a straightness datum. This can consist of some form of datum bar that is usually lapped or precision ground to a high straightness tolerance. On small portable instruments this is not always a good option and can add to the expense of the instrument. In these cases, it is possible to use an alternative means of datum. This is a skid.