After polishing an ABS print for a weekend, I decided there should be a faster method than polishing with ever finer grit by hand..
(For more information about this polishing job and model, please see here)
So when cold acetone vapor techniques came around, I decided to give it a try. Turns out that for delicate/mechanical models you really don't want them in the vapor for too long, which means you probably want to sand them a bit first to get nice results. And you also want some kind of rotating device probably, to avoid the tops of objects to collapse inwardly..
But if we have to sand anyway, and we have a pretty precise printer (as shown below), do we still need acetone vapor to get a nice finish..? While experimenting a bit, I found that for objects printed on my kossel mini, it's pretty quick to sand with grit 150 or so (to get rid of any ridges), then with 300 or so (to give a much smoother feel) and then to finish things off with a bit of steelwool. The result is an almost lego-like (though matte) finish.
In the meantime, I actually tried a vibrating tumbler (with some serious cutting action, but it didn't make a scratch) and various dremel brush heads, but so far nothing I've tried comes close to good old manual sanding. I'm sure that in the future there will be a faster (chemical?) smoothing process, but for now I will stick with manual sanding.