For many applications, measuring the surface roughness of investment castings is a critical success factor. Surface roughness can be measured utilizing the Ra – Roughness Average – or the RMS – Root Mean Square. Under high magnification, microscopic peaks and valleys can be seen on the surface of a casting. Ra measures and averages the sizes of the peaks and valleys. The RMS method calculates the Root Mean Square of the peaks and valleys, a more complex but better approach in some cases. It is impacted more by one or a few large peaks and valleys than the Ra.
