Using acetone on an ABS print is a quick, easy, and not so dirty way to smooth the layers that are created in the printing process. I generally dont mind having layers in the kind of printing I do, but now and then, something like this octopus comes along and it just doesn't look so natural with all those calculated ridges and striations.
To smooth out these lines, all you'll need is acetone and one of these reusable, refillable empty marker pens. Note that acetone is flammable and use general precaution with regard to ventilation and skin contact. Click here for a full MSDS on acetone.
To load the pen, unscrew the cap (reverse hand thread on this type), and fill it up. To stabilize things, it helps to print out and use a stand that we posted on Thingiverse, here. After your pen is loaded up, screw the tipped cap back on and depress the felt tip against an appropriate work surface (acetone dissolves more than ABS!). Once the tip is soaked, you're ready to start smoothing your print. The trick is to work the acetone in 15 or 20 second sessions, followed by a one to two minute pause to let the acetone evaporate so the softened ABS can harden back up again. If you continue to manipulate the softened ABS, it can start to get a little too pliable. It only takes a couple of minutes to get the hang of it and generally its a very forgiving process. One interesting side effect of using acetone on ABS prints is that your print will likely be glossy. This can easily be removed with scotch-brite or a sanding sponge. In some cases, this is desired of course, as the shine on this octopus makes it look slippery, slimy, and all the more real!
All in, I probably spent about 4 minutes smoothing this guy out, I have no doubt that if I had spent 10 minutes, all remaining lines would no longer be visible. It's also noteworthy that this octopus was printed with a .4 nozzle. The fatter your nozzle and the more pronounced your layers are, the less effective this method will be. Enjoy!