How do I smooth 3D printed objects? What is the best / common method to do this?
Abrasive blasting is the only other method I can think of which you haven't said you don't want to try.
It is certainly the easiest method provided you have access to one.
Different forms of abrasive blasting include:
- shot blasting (metal shot) - I suspect it would be far to abrasive but I've never tried it.
- sandblasting - you have to be careful but this is basically sandpaper attached to a wand. I've used it with great success.
- bead blasting - using plastic beads. It might actually be the best option but I've never tried it.
- media blasting - usually uses ground up shells. Might work but I've never tried it.
Get a rock/jewelry tumbler and some tumbling media such as stainless steel shot, and try tumbling your print.
For 3D printed plastic, your print will (a) need to be sturdy, and (b) not have any fine details or small parts that you don't want to be worn away. With metal you will tumble it for hours in order to smooth and semi-polish the surface. With plastic, I would recommend a much shorter time period.
One person tried this using screws as his tumbling media, and has some interesting results to show for it. Part 1, Part 2, Part 3, Part 4. Basically, you can get a metallic coating on your plastic print that is made up of tiny bits of the tumbling medium. You'll need to add a protective coating to keep it from rubbing off, but it's cheaper than buying metallic filament.
(Thanks to Mark Walter's comment for the linked articles)