Rotary Rock Tumbler Instructions

The most common type of rock tumbler is a rotary drum tumbler. It polishes rocks by simulating the action of the ocean waves. Rotary tumblers polish rocks much more quickly than the ocean, but it still takes some time to go from rough rocks to polished stones! Expect the process to take at least a month from start to finish.

Use these instructions as a starting point for your tumbling. Keep records of the type and quantity of rock and grit/polish, and duration of each step. Use this information to refine your technique for the best results.

Rock Tumbler Materials List

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Vibratory Rock Tumbler Instructions

By Anne Marie Helmenstine, Ph.D.

• Rotary tumbler
• Rocks (all the same approximate hardness in a load)
• Plastic Pellets
• Silicon Carbide Grits (You may add a 400 mesh SiC step, if desired, before polishing)
• Polishing Compounds (e.g. alumina, cerium oxide)
• Lots of Water

How To Use a Rock Tumbler

• Fill the barrel 2/3 to 3/4 full of rocks. If you don't have enough rocks, you can add plastic pellets to make up the difference. Just make sure to use those pellets only for coarse polishing and use new pellets for the polishing stages. Keep in mind that some plastic pellets float, so make sure you add them to the proper volume before adding water.
• Add water so that you can see it between the stones but do not completely cover the stones.
• Add grit (see chart below).
• Make sure your charged barrel falls within the weight allowance for the rotor to be used.
• Each step runs for at least a week. For the first step, remove the barrel after 12-24 hours and open it to release any gas buildup. Resume tumbling. Don't be afraid to open the barrel periodically to make sure a slurry is forming and to check the progress of the process. The tumbler should have a uniform tumbling sound, not sound like tennis shoes in a dryer. If the tumbling is not uniform, check the level of the load, formation of slurry, or mixture of rock sizes, to make sure these things are optimal. Keep notes and have fun!
• Let the rough grind (60/90 mesh for hard stones, start with the 120/220 for soft stones) run until all of the sharp edges have been knocked off the stones and they are pretty smooth. You can expect to lose about 30% of each stone during the tumbling process, with almost all of the loss during this first step. If the stones are not smoothed after 10 days, you will need to repeat the step with fresh grit.
• After a step has been completed, rinse the stones and the barrel thoroughly to remove all traces of the grit. I use an old toothbrush to get into the hard-to-reach areas. Set aside any stones that are broken or have pits or cracks. You can add them to the first step of the next batch of stones, but they will diminish the quality of all of your stones if you leave them in for the next step.
• For the next step, you again want the rocks to fill the barrel 2/3 to 3/4 full. Add plastic pellets to make up the difference. Add water and grit/polish and proceed. The keys to success are making certain there is no contamination of steps with grit from the previous step and avoiding the temptation to move on to the next step too early.

Helpful Tips for Perfectly Polished Rocks

• Do not overload your tumbler! This is a leading cause of belt breakage and motor burn-out. When in doubt, weigh your barrel. A barrel for a 3-lb motor should not exceed a weight of 3 pounds when charged with rocks, grit, and water.
• Oil the tumbler bushings with a single drop of oil, but do not overdo it! You do not want oil on the belt, as this will cause it to slip and break.
• Resist the temptation to tumble rocks with cracks or pits. Grit will get into these pits and contaminate subsequent steps, ruining the polish of the entire load. No amount of scrubbing with a toothbrush will remove all of the grit inside a pit!
• Use a balanced load that includes both large and small rocks. This will improve the tumbling action.
• Make sure all rocks in a load are of the same approximate hardness. Otherwise, the softer stones will be worn away during the polishing process. An exception to this is when you are purposely using softer stones to fill/cushion a load.
• Don't wash grit down the drain! It will create a clog that is impervious to drain cleaner. I rinse the grit steps outside using a garden hose. Another option is to rinse the grit into a bucket, for later disposal somewhere other than your plumbing.
• Don't reuse grit. Silicon carbide loses its sharp edges after about a week's tumbling time and becomes useless for grinding.
• You can reuse plastic pellets, but take care to avoid contaminating the polishing stages with grit. Use separate plastic pellets for these stages!
• You can add baking soda, Alka-Seltzer, or a Tums to a load to prevent gas build-up.
• For smooth river rocks or for any softer stones (e.g. sodalite, fluorite, apatite), you may omit the first coarse grit step.
• For softer stones (especially obsidian or apache tears), you want to slow the tumbling action and prevent the stones from impacting each other during polishing. Some people have success adding corn syrup or sugar (twice as much as the amount of prepolish and polishing agent) to thicken the slurry. Another option is to polish the stones dry (as in no water) with cerium oxide and oatmeal.

Are you interested in using a vibratory tumbler to polish rocks? Then try these instructions instead.