Rock Tumbler Instructions

Part 1: Introduction & Rotary Tumblers

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.

Materials List

• 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

Procedure

• 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

• 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.

Part 2: Vibratory Tumblers

Vibratory rock tumblers, such as those made by Raytech and Tagit, can polish rocks in a fraction of the time required by rotary tumblers. They also result in polished stones that retain the shape of the rough material, as opposed to the rounded shapes obtained by rotary tumbling. On the other hand, vibratory tumblers tend to be a bit more expensive than their rotary counterparts. However, if 'time is money' and you want to retain more of the shape and size of the original material, then a vibratory tumbler may be just what you need.

Materials List

• A vibratory tumbler.
• Rocks. You will get better results with a mixed load that includes both small and large rocks.
• Filler. Plastic pellets are great, but you can use small rocks having the same or lesser hardness as your load.
• Silicon carbide grit, pre-polish and polish (e.g., tin oxide, cerium oxide, diamond).
• Soap flakes (not detergent). Ivory soap flakes are recommended.

Procedure

• Fill the bowl of the tumbler about 3/4 full with your rock.
• If you do not have sufficient rock to fill the bowl to the 3/4 level, then add plastic pellets or other filler.
• Add the required amount of SiC (silicon carbide) grit and water. See the table below to get a sense of how much is needed. If you have the instruction manual that came with the tumbler, start out with those quantities. Keep records, so if you make changes you will know the effect the changes had on the polishing.
• Place the lid on the tumbler and run the vibrator. Let it run for a day or so and make certain that a slurry is forming. Evaporation will occur, especially if the external temperature is hot, so you may need to add water from time to time to maintain the slurry consistency.
• When the rock has achieved the desired smoothness and roundness, remove the load and rinse the bowl and the rocks thoroughly with water.
• Return the rock to the bowl, add a tablespoon of soap flakes, and fill the bowl with water to the top of the rocks. Vibrate the mixture for about half an hour. Rinse the rocks and the bowl. Repeat this step two more times.
• Return the rocks to the bowl and proceed to the next polishing step with the next grit (see the Table).
• After the final polish step, perform the washing/rinsing process and allow the stones to dry.

Here are some conditions, intended for a 2.5 lb tumbler. You can adjust the quantities for your specific needs. The durations for each step are approximate - check your load and keep records to find the conditions that work best for you. Experiment with different polishing compounds to find the type that works best for your stones.

*Use a slow speed for all steps when polishing stones with Mohs hardness of 6.5 or lower (peridot, opal, lapis, obsidian, apatite, etc.).

Helpful Tips

• Make a balanced load that includes for large and small rocks. For a 2.5 lb bowl, sizes from 1/8" to 1" work well.
• A proper slurry is needed to get the best polish in the least time. If there is too little water, then the thickness of the mixture will prevent proper movement, thus slowing the polishing action. Too much water results in too thin of a slurry, which will result in a much longer time to achieve a polish. The grit may settle out of the mixture altogether.
• Never wash grit down the drain!
• Plastic pellets may be rinsed and reused, but you cannot reuse grit.

Part 3: Tumbling Jewelry

You can use a rotary tumbler to polish jewelry and to remove burrs from jump rings or other metal components.

Materials List

• Small rotary tumbler and barrel.
• Soap (not detergent). Ivory soap flakes are recommended.
• Polished steel shot. You want enough to fill the barrel about halfway.

Procedure

• Pour the shot into a clean barrel to about the halfway mark.
• Add enough water to cover the shot plus about 3/4 inch.
• Add a tablespoon of soap flakes.
• Load the jewelry and/or components into the barrel. You want them to be able to tumble, so pack them loosely.
• Seal the barrel and let the tumbler rotate for 6-8 hours.
• When the pieces are sufficiently polished, remove them from the tumbler and rinse them well with water.

Helpful Tips

• Keep your steel shot covered with soap and water. All it takes is a few hours exposed to air for the shot to develop rust.
• Don't polish more than one chain at a time unless you derive pleasure from untangling some serious knots. You can add other jewelry in with a chain (earrings, rings, components), just don't polish chains together.
• If you use the same barrel for jewelry as you use to polish rocks, make certain that the barrel is absolutely clean. Otherwise, you may find yourself scratching your jewelry rather than polishing it!
• Remove chemical 'antiquing' before polishing. Otherwise, a chemical reaction can cause green deposits to coat nooks and crannies.
• Use extreme care if you are polishing plated or filled components (e.g., silver-plated or gold-filled). You run the risk of wearing or chipping the outer layer of metal.
• Don't tumble components with stones, as they can become scratched or dislodged from their settings.