Rock Tumbling Instructions for Rotary Tumblers
These Step by Step directions will work with any rotary rock tumbler. The specific measurements provided for abrasive materials (grit & polish) is for 3 pound barrel capacity machines. You can adjust the media amounts with the inserted chart. All of the guidelines and approaches are good practice for any rock tumbling project.
Media Amount Adjustment Chart (for generic tumbler)
Some tumblers require different amounts check here for your specific tumbler
| Barrel Capacity (pounds) | Step 1 Coarse Grit | Step 2 Medium Grit | Step 3 Pre-polish | Step 4 Polish |
| 2 | 2 oz | 2 oz | 1.5 oz | 1.5 oz |
| 3 | 3 oz | 3 oz | 1.5 oz | 1.5 oz |
| 4 | 4 oz | 4 oz | 2 oz | 2 oz |
The above chart is a general guideline to abrasive media measurements. The correct amount of grit and polish to use will vary by project task. Hard rocks and particularly rough rocks may require additional grit to be added at some point in the process.
Applicable Instructions
The following are the most common instructions for general rock tumbling in Rotary Tumblers. Many variations can be found in regard to tumbling instructions that make adjustments for different tumbling equipment and different types of rocks. The most important tips are standard. Your tumbler manufacturer may have specific instructions for your tumbler. Presented here are general guidelines and the most common consensus on tumbling methods. You might find the rock hardness information helpful on the Mohs Scale reference.
Be sure to see our grit kit designed specifically for rotary tumblers
You will see in some of our kits that offer extra items, some additional steps and guides to the tumbling process.
Good Rock Selection
The tumbling process starts with good rock selection. Pick rocks that are of the same hardness and similar size ratio (the biggest should be no more than twice the smallest) to coordinate their development in the tumbling process. Gather enough rocks to fill your barrel between 2/3 and 3/4 full. Avoid using unusually odd and non-rounded shaped rocks with the more common rounded shapes as these will be more difficult to sculpt.
Four Step Process
Rotary tumblers use a four step goal oriented tumbling process:
- Coarse Grind
- Medium Grind
- Pre-polish
- Polish
Between each of the four steps remove, thoroughly rinse your rocks, clean out the barrel and remove any grit or rock debris. This is really important as the coarser grits from one step will act adversely in proceeding steps,scratching rocks as you are refining them with finer media. As always, it is advised not to throw used grit down a drain as plumbing will be damaged. Use a bucket and a screen to collect used grit and slurry.
Step One (Coarse Grind)
The goal of this step is for all surfaces of your rocks to be well-rounded.Place rocks in the tumbler and add the 60/90 silicon carbide grit. You are looking to round your rocks in this step over 7 to 10 days. The Grit to rock ratio here is 2 tablespoons of grit per pound per pound of rock. Add water until it is just below your top layer of rocks. Seal the barrel and invert it to check for leaks. Once the tumbling starts watch for a few minutes to be sure there are no leaks. Proceed with tumbling, and at the early days if this step, check daily on the progress by opening and inspecting the barrel. If the barrel appears to physically swell, open it to vent the buildup of gas which may naturally occur, be prepared with safety glasses and precautions for that. You can also add a teaspoon of baking soda to prevent gases. Examine your rocks and slurry (the grit and water now mixed with some rock tailings). If it seems thick enough to impede the smooth tumbling of your rocks, thin it with a small amount of water. Some of the rocks may be now too small or too odd to continue working with them, so you will remove these rocks. As for the rest, once you see rounding has occurred for most or all of your rocks this move on to step 2.
Step Two (Final Grind)
In this stage, your objective is to finalize the shaping process to your satisfaction. You will eliminate any additional imperfections and blemishes that may have remained after the initial step. Typically, this phase lasts for a duration of 7 to 10 days as well. To begin, reintroduce your cleaned rocks into the barrel. Add a 120/220 silicon carbide grit in the same proportion as Step One, using 2 tablespoons per pound of load. Fill the barrel with water until it reaches the bottom of the top layer of rocks. If you encountered any issues with gas buildup previously, add a small amount of baking soda as a preventive measure. Seal the barrel and tumble the contents as you did before. The consistency of your slurry should be slightly thinner than in the previous step, depending on the softness or fragility of the materials being processed. Once again, your goal in this stage is to ensure that all the scratches from the initial step are polished away, resulting in a smooth and matte finish for the rocks. You may find it helpful to use a magnifying glass to inspect their smoothness.
Step Three (Pre-polish)
In this step, the goal is to make the rocks very smooth. Start by following Steps One and Two, and put clean rocks in a clean barrel until it’s full. To achieve this, use a pre-polishing material like silicon carbide 500 or aluminum oxide 500, adding about 1 tablespoon for every pound of rocks. Then, add water until it reaches the bottom of the top layer of rocks. The recommended time for tumbling in this step is up to 7 days. It’s important to check the consistency of the mixture and the progress of the rocks every day or two. Some rocks may become smooth and shiny sooner, so you can remove them earlier. If you’re working with softer rocks, you may need to do a second pre-polishing step or increase the tumbling time slightly. At the end of this step, make sure to thoroughly clean the rocks and barrel. The finer grit used in this stage can leave residue that might affect the final polishing results.
Step Four (Polish)
By this time your rocks are looking pretty good and ready for that lasting final shine. You have been extra diligent on cleaning the rocks and barrel. Place your rocks in the tumbler and add Aluminum Oxide Polish, about 1 tablespoon per pound of rock. Step four takes up to seven days but be sure to check the rocks as you are proceeding because some will be finished earlier. The best check for completed rocks is that they look as now as they would if wet. Once that is the case you are done with this step. One final detail, its best to clean up now by cleaning your equipment thoroughly before everything dries and encrusts. So you’ll be ready for your next project with rock tumbling.
Final Thoughts
In addition to the instructions above, it may be beneficial and interesting to see our section on the Science of Rock Tumbling. This is a behind the scenes look at the technical and scientific foundations of the rock tumbling process.
Instructions for Vibratory Tumblers are found here.
General Tips for Tumbling and doing Pretty Much Anything Else
Belief that you can make something great
Patience
Attention to detail
More Patience
For other applications and uses of your rock tumbler look here