Some more examples, here the top part has been resin coated and the lower half has not. No primer was applied to either section.
Could have used a bit more cleaning before I painted it, but these parts have been sitting around for a while and I am just using them to test paint, primer, and finishing methods.
So for me it depends on the parts I'm trying to clean up. If they are nice detailed resin parts, I just start with 220 sand paper and some really fine files.
For the bigger grosser fdm prints, say like a helmet, I start with 80 grit paper and knock down the high spots, then I'll bondo the really rough areas, the next step for me is to Polyprime the entire thing. Polyprime, for those that don't know, is a really nasty heavy primer. It's a catalyzed polyester automotive primer, basicly sprayable bondo. After that cures I start sanding with 120 grit sanding sponges. After the first go of 120 I'll bondo any divits still in the sufrace. I'll then sand the bondo down smooth with 120 grit and work my way up to 220. Next I prime with a lighter rattle can primer and then alternate sanding and priming until I get a nice finish. My last steps are to do one last coat of rattle can primer and then sand that with 600 grit sanding sponges.
This is something I do professionally, so I realize not everyone has access to the same materials and tools that I do but this is my process. One thing that might help, is breaking the parts down befor they are printed. I find it works better if you print the finer detail parts separately, maybe even on an sla printer and then it's easier to body shop the less detailed fdm prints. Also, have lots of files for getting down into fine details or panel lines. One last tip, I wear thin protective gloves when I sand. After a day of sanding my hands will crack and bleed otherwise.
Thanks for this guide skahtul, I got a Prusa Mini not long ago so I'm just beginning to learn about finishing printed pieces. Sanding and filler primer definitely works, but it's not fun. I just put in an Amazon order for the resin and bulk brushes.
