" May i know what's the easiest way to restore the surface of a piece of acrylic that was previously milled?
Can i make it transparent again just by sanding or do must it be buffed? For the former what is the recommended grit size to start with?"
How rough is the surface? What I've done in the past is to start off with 400 grit wet/dry sandpaper, and WET sand the surface. Then progress to 600, 1000, and 1200. WET sand, and don't go to the next step until all the scratches are removed from the current grit. If you're not happy, then you could try glazing compound like they use for car finishes. Be very careful if you do this with an electrical buffer
- it is very easy to overheat the surface of the plastic which will mess it up.