I have brushed most of my ABS prints with MEK. I always wear an appropriate mask, gloves, and safety goggles. Brushing is ultimately not that great since it can leave a white film on the parts, and because outer dimensions are changed a little bit by the force of the brush.
I read about acetone vapor polishing. I first read that MEK vapor is generally a bad idea. I am using “MEK Substitute” from Home Depot, but I understand that the stuff is more harmful even than acetone. I am not a chemist, but I know enough to not do something if I read that it is harmful. Acetone vapor is also dangerous both as a harmful chemical to inhale, and because the vapor is very flammable, and could even cause an explosion if contained during ignition. I wore a gas mask, safety goggles, AND a face mask while working on this system.
I set up an acetone vapor polishing system using a vacuum jar covered with a glass sheet. I used my (now spare) RepRap heated bed and a PID controller to warm the acetone up to 90C. I moved the electronics away from the acetone to avoid possibility of ignition.
You can see in the next picture that I did not clean up the print before trying acetone vapor polishing on the first model. This is a bad idea because the filament threads ball up and stick to the model during polishing. It’s best to use a razor and completely clean up the model before polishing. That way the finished outer surface is as clean and smooth as possible.
I waited for vapor to condense on the top window to know that the container had vapor ready to work on my ABS model.
The first print I used to test the polishing was a Staford bunny with a skin that was too thin and with too little infill. I had 2 perimeters and 0.05 infill. This printed quickly, but had some holes in it. I know that with brushing MEK, holes in the print are disastrous. Once any solvent gets inside of the print, it collapses. This is apparently also true for acetone vapor. The result was a sad little bunny.
The second print that I tried to polish had three perimeters and 0,25 infill. There were still a few minor holes, so I only left it in the vapor for about 30 minutes. This was not long enough to smooth the spaces between layers, but it did shine the model pretty nicely.
I have increased the number of perimeters in SLIC3R to 4, and plan to polish a new model for a long enough time to really smooth it completely.
As many people suggest on the internet, please BE VERY CAREFUL heating acetone and creating vapor. This stuff can hurt you in a number of different ways.