If the finish of your precision cast parts is an important consideration, it is critical that your foundry utilizes accurate investment casting surface roughness measurements. Surface roughness is typically measured by Ra, Roughness Average, and RMS, Root Mean Square. Ra calculates the average of the peaks and valleys on the surface of the parts. These are very small and not usually visible to the naked eye. RMS utilizes the root mean squared of the peaks and valleys and reacts more to a small number of bigger peaks (flaws). The best option depends on the part specification requirements.
