The problem with surface finish is that it gets deep very quickly. Many people talk about the “finish” or the “roughness” of a surface as if it were one unique thing. For most people, surface finish means the most common measure, which is average roughness, or Ra. But there are something like 50 to 60 different ways to measure short wavelength “roughness” characteristics. There are also longer wavelength “waviness” characteristics, “spacing” characteristics, and a whole bunch of “hybrid” characteristics, all measured by different parameters—over a hundred in all—with most defined by some international, national, or corporate standards.
Then there are the instruments used to measure these parameters. While Ra can be measured by a basic handheld gage costing around $2K, sophisticated high-end systems that can stage parts, automate measurement sequences, and measure every parameter known to man can run as much as $150 to $200K. Beyond these are CNC systems that move the part around to allow measurements at many locations, and these can go for anything up to $300 or $400K.