How much of a surface do you need to measure in order to accurately describe its roughness? For typical surfaces, the standards suggest an evaluation length 5 times longer than the roughness cutoff. But if you are measuring a narrow feature or part, such as an O-ring groove or washer, the surface may be smaller than that 5X length.
In this video we show you how to determine the “evaluation length” for measuring roughness on a typical surfaces. We then introduce several options for measuring texture on smaller surfaces, and we point out some pitfalls that can lead to incorrect evaluation of roughness and waviness.