I’ve been wanting to try out finishing printed parts in a tumbler. This is a polishing process often used for things like rocks and metal parts, where the part is placed in a barrel with some media and rotated for a few hours. The media consists of chunks of some kind of material, like ceramic, plastic, or walnut shells. During tumbling the media abrades the part, polishing it.
I’ve heard mixed reports of the effectiveness of this for ABS and PLA, and have been reluctant to spend $150-$200 for a small tumbler than might not even work that well. Then, thanks to some YouTube links, I realized I already had a large tumbler next to the washing machine.
I went to the local Harbor Freight and bought a 5lb jar of ceramic media. Ceramic is recommended for aggressive deburring of metal. Plastic is much softer than metal, but removing the layer lines requires removing more material than you would usually want if you were just polishing. I also bought a 2 gallon barrel and a cheap doormat. I cut the mat and used it to line the barrel so the ceramic wouldn’t make so much noise rattling against the plastic barrel.
To test it, I used a ring that I had printed at .1mm layers. It is about 2mm thick, 40mm high and 70mm across. I wrapped the barrel in pillows and quilts, and placed it in the middle of the dryer. You can position it so that it rolls, or turns end over end. End over end will provide more aggressive action if you feel like you would need it.
I set the dryer to Air Fluff (no heat) and set the timer as high as it would go, which is only 1:20:00. I ran it enough times to total about 8 hours of tumbling.
It came out smoother than I expected. It has a matte finish, and a feel that isn’t exactly soft, but very friendly to the touch. The layer lines are only visible if you look hard for them. It would take only a quick exposure to acetone to smooth it the rest of the way, and if you still wanted a matte finish rather than glossy, an hour or so in the tumbler would be enough to take the shine off.
The downside to this method is that it will round off sharp edges. You might want this effect for instance if your part is something that will be held and handled. Also it works better with high resolution prints. The one below is .3mm, and was only in for about 2:40. The edges are already rounded, and the dust is getting caught in the layer lines. It might be able to reach the same finish as the ring, but take much longer.
A vibratory tumbler should be more gentle, though maybe less effective because of it. However it would be easier to leave on for long stretches like overnight. These results give me a little more confidence in the thought of ordering one such as this one from Harbor Freight – http://www.harborfreight.com/18-lb-vibratory-bowl-with-liquid-drain-hose-96923.html I think it would definitely be good for preparing prints for acetone vapor finishing (next post).