After experimenting with different filaments I knew I had to get a rock tumbler. The surface finish of 3d-prints can be improved and altered by sanding and grinding, but detailed prints would take forever.

I decided to make a printable rock tumbler.

Initially I wanted the tumbler to be able to handle a fullsize print from my biggest 3d-printer, which was 20cm cubed at the time. This would probably be too heavy for the motor I had and I downsized the volume of the barrel to 30cm long and 12cm in diameter. It would still be able to handle most of my prints anyway…

After some experimenting with the basic proportions in 3d, I made the baseplate 63cm x 38cm. This would accommodate the motor and drive chain, rollers and the tumbler barrel, present size and future upgrades in mind.Rock Tumbler 01A bigger motor could drive a bigger barrel, and all I would have to do is change the distance between the rollers.Different Sizes 1Overnight print of rubber rollers, gone wrong.Rock Tumbler 02All parts printed.Rock Tumbler 03Gluing and securing one side of the rig.Rock Tumbler 05Motor and motor controller in place.Rock Tumbler 12To avoid the center nut from spinning through the plastic during heavy load, extra nuts were added around the axel. These have to be hammered into the print for the tightest possible fit.Rock Tumbler 06 BMaking the drive axel.Rock Tumbler 07Rock Tumbler 08THE BARREL
First I tried to make the barrel out of plumbing/plastic tubes. This didnt work… Getting the end cap off was very hard, almost impossible. Even with generous amounts of grease and silicone lube.Rock Tumbler 09I turned to my new-found welding skills and used a 1,2mm steel sheet which I folded/broke manually into an octagon. That is, I tried to make an octagon… it didnt exactly turn out completely symmetrical.Rock Tumbler 10Rock Tumbler 11Rock Tumbler 26To make the necessary geared rings around this asymmetrical barrel fit perfect, I 3d-scanned the octagonal cylinder using photogrammetry. Reflective surfaces are close to impossible to scan so I first painted the surface and added some distinguishable patterns with a sharpie.Rock Tumbler 14Rock Tumbler 15Rock Tumbler 15BFar from perfect, but good enough for a 360 degree photo shoot. I shot one series of photos from a low angle, one head on and one at a high angle.Rock Tumbler 16After importing 128 photos into the photogrammetry-software it calculated all the camera positions and generated this pointcloud.Rock Tumbler 15CMillions of points! These are used to make a precise 3d mesh/model of the barrel.Rock Tumbler 15DWith the excact shape and form I could make the “geared-rings” that drive the barrel. These four rings are all unique along the lenght because of the asymmetry of the octagon.Geared-Rings-BarrelAttaching the four “gear-rings” at the correct distances around the barrel.Rock Tumbler 18 BThe end cap is secured with 8 wing nuts.Rock Tumbler 27

I also modelled and printed the drive belt. This was a challenge… The flexible filament I had at hand was PLA Flex from Ultimaker, and this turned out to be too stiff for this purpose. No matter how wide or thick I made the belt they all snapped and broke after apx. 4 hours of tumbling.Broken BeltsSo I bought a roll of PolyFlex from Polymaker. This was much softer and holds up quite well, even after hours of tumbling the belt is still intact and shows no signs of tearing.Belt Drive BTumbling.Tumbling

The whole point of a rock tumbler is to have some kind of grit media grind and polish down the surface of the objects over several hours of tumbling. I experimented with different types of grit, including nails and screws…Grit NailsGrit ScrewsResults after about 8 hours with improvised grit. The stainless steel filament got an obvious shine, as did the copper filament though with the wrong coloration… This is most likely because the nails/screws are coated with some kind of nickel finish that deposits on the objects…? Result 01I have recently aquired some professional grit, silicone carbide. Coarse 60, medium 180/220, pre-polish 500 and final fine polish 1200.Grit AmazonIll post the results when done………………………… 

3d-files and real-time model available HERE.