There was a time when most 3D printers used ABS plastic. It stinks, is probably bad for you, and tends to warp unless printed in a heated enclosure. So most people have gone to something else, mostly PLA. But ABS also dissolves in a readily-available solvent, acetone, and this is useful for smoothing the layer artifacts from a 3D print. [3DSage] has a technique that works for PLA or — he says — probably any filament. You can see what he’s doing in the video below.
The video starts out with a recap of things most Hackaday readers will already know. But hang in there because at about 1:20, he reveals his method.
The technique involves using plastic-compatible paint and fast-drying polyurethane. He quickly sprays a thin coat of paint and then a thin coat of polyurethane on the part and uses a fan to rapidly dry the mixture before it can run. The two sprays merge to form a coating. He does apply several coats, leaving half an hour to dry between layers, and waits overnight before applying the final coat.
The results look pretty good. This is more like a coating than truly smoothing, but it does fill in the gaps and ridges nicely. As [3DSage] points out, you can print with a larger layer height, and you can change the final color by just changing paint colors.
It certainly looks easy enough to try out. A trip to a big box store and a fiver should put you in business. Our own [Donald Papp] has done something similar with UV resin. The paint method does seem safer than torching your prints.