I see. There seem to be more precise ones http://www.pmtnow.com/end-mill/micron "Micro Tool has been able to manufacture end mills as small as 5 microns in diameter" Not sure if this is the brand he is using though, just googled to find one. Of course there's probably more to precision than step precision and mill bit cutter part diameter and I would still love to learn more on what those variables are and what make a micromachining CNC optical grade. Unless the variables are "only" the ones mentioned already (temperature, humidity and vibration isolation). I also understand everyone's examples, but I still don't understand why we seem to treat the requirements of all optics equally. Are cheap chinese M12 lenses for camera modules such as in the below link and DSLR lenses made with the same optics grade CNCs and requiring the same precision? Another project where I need molds, PMMA fresnels with a custom fresnel ring setup Do these fresnels require the same optical grade molds? https://www.alibaba.com/product-deta...63a133e9cPsm82 if I was a company offering lens and lens mold manufacturing for any kind of lenses then I could probably afford and would probably need such a measuring equipment, but for the lenses I need this example alone doesn't convince that you'd need a measuring equipment with a 10 nanometer accuracy when 1 micron is 1000 nanometers. It comes back to my question of is there a reason to treat all lenses equally in terms of its manufacturing. If this was addressed already and flew over my head then I apologize.