How to Use This Rock Tumbling Grit Planner
This tool tells you exactly how much grit to add at each tumbling stage, how many days each stage should run, and which date to expect completion — all adjusted for the actual hardness of your stones.
- Enter your batch weight — the pounds (or kg) of rough rock you are putting in the barrel. Do not include ceramic media or plastic pellets in this number.
- Select tumbler type — rotary tumblers use 2 tbsp grit per pound per stage; vibratory tumblers use ½ tbsp per pound per cycle.
- Choose your stone type or Mohs hardness — this adjusts stage durations. Agate and jasper (Mohs 7) take much longer in coarse grit than fluorite (Mohs 4).
- Set a start date — the planner generates a projected end date for every stage.
- Check options — enable a repeated coarse stage if your stones are very angular or pitted; enable burnishing (soap wash) for a final shine.
Review the shopping list to know how much grit to buy before you start. Print or copy the plan and tape it to your tumbler.
How Stage Durations Are Calculated
The base durations come from published lapidary guidance: rotary coarse = 7–10 days, medium = 7 days, fine = 7 days, polish = 7 days. This calculator applies a Mohs hardness multiplier to the coarse stage (the stage most sensitive to hardness): harder stones require significantly more time because silicon carbide removes material more slowly from dense surfaces. Subsequent stages are less affected, so only a small multiplier is applied there. The multipliers used:
- Mohs ≥ 7.5 (quartz, agate): coarse ×2.0 (14–21 days), medium ×1.2
- Mohs 6–7 (jasper, feldspar): coarse ×1.5 (10–14 days)
- Mohs 5–5.9 (obsidian, lapis): coarse ×1.0 (7–10 days)
- Mohs 4–4.9 (fluorite): coarse ×0.6 (4–6 days)
- Mohs < 4 (calcite, marble): coarse ×0.4 (3–4 days) — check frequently to prevent over-tumbling
These are planning estimates. Always inspect your stones at each stage and extend the run if surfaces show pitting, scratches, or uneven rounding.
Which Polish to Use for Your Stone
Polish type matters — using the wrong compound can leave dull or scratched results:
- Aluminum oxide (TXP) — the standard, works on most stones Mohs 5+: agate, jasper, quartz, petrified wood, obsidian
- Tin oxide — recommended for soft stones (Mohs 3–4): fluorite, calcite, marble, alabaster. Gentler and produces a better finish on low-hardness materials.
- Cerium oxide — best for glass, obsidian, and Apache Tears. Produces exceptional brilliance on vitreous materials.
- Chrome oxide — specialized use for jade and nephrite (hard, dense stones)
This planner recommends a polish type based on your selected Mohs value. Never mix polish types in the same barrel.
Frequently Asked Questions
How much grit do I use per pound of rock in a rotary tumbler?
The standard is 2 level tablespoons of silicon carbide grit per pound of rock for the coarse (60/90), medium (150/220), and fine (500F) stages. The final polish (aluminum oxide) also uses approximately 1–2 tablespoons per pound. Never add extra grit hoping to speed things up — too much grit can slow the tumbling action, not accelerate it.
How long does each stage of rock tumbling take?
In a rotary tumbler, the standard base is 7–10 days per stage. The coarse stage varies the most: hard rocks like agate or jasper (Mohs 7) may need 14–21 days; soft calcite (Mohs 3) may round in 3–4 days. Medium, fine, and polish stages are more consistent across hardnesses. Vibratory tumblers run far faster — medium grit cycles run 12–24 hours and are repeated 3–7 days total, with fine and polish each taking 2–3 days.
What grit sequence should I use for rock tumbling?
For a rotary tumbler the standard 4-step sequence is: Step 1 — coarse (60/90 silicon carbide) shapes the stones; Step 2 — medium (150/220 silicon carbide) removes coarse scratches; Step 3 — fine (500F silicon carbide) prepares the surface; Step 4 — polish (aluminum oxide, tin oxide, or cerium oxide) creates the final shine. Vibratory tumblers typically skip coarse and start at medium grit.
Can I reuse rock tumbling grit?
No — silicon carbide grit breaks down as it works and cannot be reused for the same stage. The slurry from Stage 1 is sometimes left in for the start of Stage 2, but fresh grit is needed for each new cycle. Polish (aluminum oxide) can be reused a few times if the barrel is thoroughly cleaned between batches — but it eventually loses effectiveness and must be replaced.
How do I know when a stage is done?
Check the slurry: rub it between your fingers — if you can't feel grit particles, the grit has broken down and the stage is effectively finished. Then rinse and inspect the stones. Edges should be rounded (after coarse), surfaces progressively smoother. Never advance to the next stage if you see pitting or uneven scratch marks — those defects will only be preserved, not corrected, by finer stages.
How much grit do I need for a vibratory tumbler?
Vibratory tumblers use approximately ½ tablespoon of silicon carbide per pound of rock per cycle — about one-quarter the amount of a rotary tumbler. They also skip the coarse stage, starting with medium grit. The total grit consumption for a vibratory batch is considerably less than for a rotary batch of the same weight.
What does "burnishing" mean in rock tumbling?
Burnishing is an optional final step where you tumble the polished stones with water and a small amount of soap (e.g., Ivory soap flakes) — no grit or polish — for a few hours to a couple of days. It removes any residual slurry or dull film from the surface and can enhance the final luster. It's especially useful if your stones came out smooth but slightly hazy after the polish stage.