Hi Daniel, Great question! To get a mirror polish finish on your copper CNC parts with a roughness of Ra0.4 µm, you need to specify this clearly both on the quoting site and in your drawing. On the quoting site, there should be a section for surface finishes. Choose the option "custom" and write "mirror polishing" and mention the roughness value of Ra0.4 µm in the "Max required roughness" section. For your drawing, make sure to include a note near the relevant part that says something like "Mirror polish finish, Ra0.4 µm." This way, the manufacturers will know exactly what you need. By doing both, you’ll ensure your parts get the smooth, shiny finish you're looking for. If you have any more questions, feel free to ask! Best,