Rock Tumblers

A look into a vibratory tumbler during the polish stage.

A look into a vibratory tumbler during the polish stage.

Rock Tumblers come in rotary tumbler or vibratory tumbler types.

They turn rough rock into polished tumbled stones.

Agate, jasper, chalcedony, quartz — almost any rock can go in a tumbler, provided it is not too soft.

The first thing to understand is rock polishing in a rock tumbler does not happen overnight. This is a longer process than many people expect.

Rotary rock tumblers typically take at least four weeks to turn rough rock into polished stones. This covers one week for each of the four grit stages, from the roughest grit to final polish at the end.

Vibratory rock tumblers are faster. You can turn rough rock into tumbled stones with a vibratory tumbler in a week or two. A lot of rockhound enthusiasts use a combination of rotary and vibratory tumblers for the best result.

Here’s a quick breakdown of the differences between rotary and vibratory rock tumblers:

Rotary Rock Tumbler

  • Operates by rotating a cylinder filled with rocks, allowing the rocks to bounce against each other and grind down in the grit
  • Takes at least a week for each stage of grit
  • “Set it and forget it” – you don’t need to constantly monitor rotary rock tumblers
  • Takes a substantial amount of grit
  • Rounds stones because of the nature of the action in the cylinder
  • Not excessively loud; can’t hear it in a garden shed

Vibratory Rock Tumbler

  • Operates by vibrating stones together inside a bowl, allowing the rocks to bounce against each other and grind down in the grit; creates a “whirlpool” effect
  • Takes only a day or two for each stage of grit
  • Requires regular monitoring to add water and make sure it is running smoothly
  • Very loud, sounds similar to being inside an airplane taking off
  • Stones retain their natural shape more and do not get rounded like they do in a rotary tumbler; this is because of the nature of the action being different

  4 comments for “Rock Tumblers

  1. Natasha Hutcheson
    November 26, 2021 at 12:05 am

    Could you please tell me approximate prices it would be for a decent version of each?

    • Mark King
      December 15, 2022 at 12:27 pm

      The chemical engineer would call these “ball mill” and “attrition mill” respectively, ball mill anatomy follows: the rotating cylinder is called the ball mill jar, the balls or other media like cylpebs are chosen for the material’s hardness and sometimes toxicity or ease of removal of traces of the milling media in the finished product (dissolves in hot water means easily removable, ditto for ferromagnetic metal like from ball bearings of a certain alloy of steel) these machines not only take ordinary stones and turn them into spectacular conversation pieces, but their raison d’etre is for reducing size of cosmetic and chemical ingredients, historically this was gunpowder ingredients, more recently mineral sunblock ingredients which qualify as nanotech materials — these require a ball mill for getting powder’s indivisible components to pass through 1000 mesh screens and such. Many cosmetics are made from milled ingredients, eyeshadows, blush, anything with pigment colorants like nail polish, and many more. The alternative is milling your coffee grinder is a burr mill, there are many varieties of milling equipment, and their use cases are generally for taking something from the size of baseballs or tennis balls and grinding it down to rice grain sized pieces or a coarse powder, like coarse corn flower you find under pizza crust. Powerful spinning blade type of grinders can get fine powders down to 400 mesh and sometimes with clever formulating, like adding anti caking agents and magnesium stearate to lubricate the rotating parts at the seals, but for anything finer than 325 mesh, you go to a ball mill. Still with me? Now you know all you need to discuss these with experts and not get the run around. Ball mill jars of the 1 gal size and up get pricey, but the pedestal that has the skeateboard wheels and some sort of transmission element like chain sprocket or rubber belt or gear for direct drive modelss, or a rubber wheel with a screw to position it at the right height so it contacts the jar to rotate it. Once you see what these look like, many of you will awaken the DIY spirit and turn off the computer to go rummage the $100 in parts to make your own, and start shopping for prison kitchen sized stock pots or salvage drums with treadmill mat liner?? Now you’re talking my language! Go huge, do massive batches, and have it pay you. Name the beast “side hustle”. None of this 1 week dwell time for the huge drum size ball mills, the enterprising operator will crank it up and find what speed the load just hugs the wall with centrifugal forces sufficient to achieve the bucket full of water staying full even if swung upside down over your head (poor man’s kettlebell), speed will be upward of 60rpm. Your maximum milling will be when the biggest balls or in your case stones travel up the wall to 80% of the total diameter of the jar wall. They will fall down and party with the payload in a manner akin to stage diving into the mosh pit. This “regime” of falling and strong collision does remove material, but it may end in tears for the more sensitive rock loving people, when they see their prized calcite smashed to pieces. Remember, to not be angry for cats being cats, they don’t care if it’s gucci, their claws needed #something#, ball mills are on this earth because they are good at size reduction of nearly anything you shovel into the jar, breaking is within the scope of size reduction. So pushing the bad boy past redline means some broken stones, but only the weak and brittle, your uglier stones will do just fine, and the more spherical will also tend to survive the brutal punishment for cheating on one’s spouse endorsed by at least 3 of the major religions. (There may be some sarcastic naming ideas here for your jar, I dunno, or at least a way to scare children: if I catch you smoking dope I’ll show you stoned!)

      Generally, if the larger components do not fall much at all but instead cascade down the rolling bolus of rocks and scratchy abrasive chunks then you avoid the kamikaze freefall regime that breaks rocks. A churning, rolling medium speed process control is safest for your rocks. There are several other fine points to discuss, like the difference between static and kinetic friction. Counterintuitive principles are a personal favorite, I love reminders that the world does not have to make sense for your benefit, a piece of wisdom I consider the litmus test for grown up or not. At some point you no longer get upset when confronted with unfairness or senseless rules and practices. If everything made sense then engineers would struggle to feed their kids.

      If some object is at rest, just sitting there minding it’s own business, but you want to violently get it the %#@]{ out of your way, the force curve required for you to impose your will on this object will start out at its highest, then settle down to a steady fraction of its max, like recent BTC charts, the regime of initiating movement is the static friction (some motors have a stated property called Kick Current, how big a slap of electricity is needed to motivate the sleeping motor to burst into action) after it is already moving, you guessed it, kinetic friction, a much lower force to overcome. This property can be exploited as a tool for energy savings, since you will need to operate the ball mill at even slower speeds to find a sweet spot when your rock spend the shortest undeniable moments at complete rest, then a moment later, under new conditions, it starts to roll. You can rip the door off your front loading dryer and find some way to attach it to he mouth of the jar so you can see in and look for the lazy rock moment. Okay, sure, buy a sheet of methacrylate or polycarbonate sheet in 3/16 or 5mm +/-, and attach it to the mouth of the jar with aluminum extrusion angle or a routered flange from plywood, and please take some photos like in Nathan Myhrvold Modernist Cuisine encyclopedic nerd’s guide to cooking anything perfectly, in which stock pots and frying pans are cut in cross section, so one can photograph the interior very nicely, showing boiling water and blanching veggies or what have you, the magic is a sheet of glass carefully glued to the pot, invisibly, and one is left to ponder how the water stays inside half a pot. I for one would love to see a ball mill in action…

      If you made it this far please comment, I tried to pack in a lot of info, which is never easy in the western world where high school’s only goals are to make you hate learning and to not trust yourself. I have the opposite mission, to inspire DIY (i.e. trust yourself) and do the best job you can (i.e. embrace learning).

      Attrition mills are the vibrating, oscillating, or agitated mills packed with abrasive media or small spheres of hardened materials in the punishing hands of a paint shaker or some other sick mind’s evil construct for torturing rocks. If you are the sadistic schadenfreude type who doesn’t mind violence against rocks, then the attrition mill might be your favorite thing in the shop. Your dwell times can be reduced to minutes in some cases, instead of the week we started with, so for smaller rocks and ADHD rock people, forrage the used process equipment sellers like ebay. It won’t take much searching. Don’t forget to check alibaba, their factories might just have a benchtop model far cheaper than a rusty used one from ebay or labx.

      I read in this blog “expensive” and “abrasive media”, these two words should not invade the same sentence in my opinion. Especially when you can toss in anything under the sun and see if it works. Industrial wastes sometimes work, for example I was given 20 metric tons of perlite fines, “just get it outta here, I need the space”. A clever rethinking of what is abrasive media, from sandblasting we could deduce that sand is a candidate, but so are walnut shells, steel grit, baking soda, slag, corundum, cerium oxide, glass frit (recycled glass after hammer milling), etc. get creative! Here are some key properties to consider: Moh’s hardness, particle shape (jagged, spheroidal, can be measured by angle of repose and angle of spatula, lower cone angle is closer to sphere shaped or low friction), bulk density, friability (you don’t care so much, but it reduces how many times it can be run (recyclability, but you need a way to separate it from rock powder, the inevitable byproduct ** the powder can be sold as aggregate for venetian plaster, concrete countertop decoration, epoxide flooring sprinkles, plastic and epoxide resin filler media, etc.), cost, where to get or buy (avoid native to Sri Lanka or Equitorial Guinea if you are in Vancouver, pick something that is a mining waste as close to home as possible, or bring a shovel to the beach. Don’t feel like going to a beach? seattlepotterysupply dot com will dazzle you with variety and great service. Masco is a masonry supply company with many suitable materials sold in huge bags at prices almost nobody will think are expensive. Keep in mind also that the hardest materials are not the only candidates, baking soda is used in titanic amounts in dedicated soda blasting equipment, it’s popular for many reasons. So why not get out there with a 20lbs sledge and crush some ceramic teacups to 4 mesh and give it a whirl, or whatever you can dream up. The wilder the material choice the higher chance of you stumbling into a utility patent and royalty income from deep sea drilling or something far stranger. Good luck and happy DIY-ing your way to a show-off tumbling system that can run the multiple stages automatically and only takes a couple of hours. Who wouldn’t buy it? I would even buy one. The person who got rich during the gold rush… know who it was? Haha, nope, the dude who sold shovels. If you make a good tumbler, the world needs you and will make you a HNWI. In case anyone though playing with rocks in the garage was somehow an unworthy way to spend precious time.

  2. Charlie Grant
    March 9, 2022 at 11:57 am

    Looking for information where I can purchase rock tumblers in Fraser valley I live in Chilliwack

    • Mark King
      December 15, 2022 at 12:28 pm

      see my post in the same section as your question.

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