How much grit should go in your barrel? Most tumbler makers print a chart in their instructions. We collected the published amounts for the tumblers our tumbler refills are made for, so you can measure each step the way the manufacturer intended.
Amounts are per barrel load, for each step. Tablespoons are level. If your model isn’t listed, start with about 1 to 2 level tablespoons per pound of rock and adjust: unbroken grit left at the end of a run means you used too much.
Lortone
Fill the barrel about 1/2 to 2/3 full of rock and add water to the top layer of rocks. Tumble 5 to 7 days per step, checking after 2 to 3 days. Lortone uses a little more pre-polish and polish than coarse grit. Refill: Lortone Tumbler Refill Kit.
| Model | Barrel | Coarse 60/90 | Medium 120/220 | Pre-polish | Polish |
|---|---|---|---|---|---|
| 3-1.5B | 1.5 lb | 2 to 4 Tbsp | 2 to 4 Tbsp | 3 to 5 Tbsp | 3 to 5 Tbsp |
| 33B and other 3 lb barrels | 3 lb | 4 Tbsp | 4 Tbsp | 4 to 6 Tbsp | 4 to 6 Tbsp |
| 45C and other 4 lb barrels | 4 lb | 6 to 8 Tbsp | 6 to 8 Tbsp | 8 Tbsp | 8 Tbsp |
Thumler’s
Thumler’s gives amounts by weight. Fill the barrel 1/2 to 5/8 full of stones and add water even with the top stones. Run coarse and fine about 7 days each, pre-polish about 3 days and polish about 7 days. Refill: Thumler’s Tumbler Refill Kit.
| Model | Barrel | Coarse 60/90 | Fine 120/220 | Pre-polish 500F | Polish |
|---|---|---|---|---|---|
| Model T, A-R1 | 3 lb (1 qt) | 4 oz | 4 oz | 2 oz | 2 oz |
| Model T-2, A-R2 (each barrel) | 3 lb (1 qt) | 4 oz | 4 oz | 2 oz | 2 oz |
| A-R6 | 9 lb | 8 oz | 8 oz | 4 oz | 4 oz |
| A-R12, Model B | 12 to 15 lb | 1 lb | 1 lb | 1/2 lb | 1/2 lb |
Harbor Freight
For the Chicago Electric 3 lb single and dual drum tumblers. Load the barrel 1/2 to 3/4 full and add water to the bottom of the top layer of rocks. Harbor Freight suggests plastic pellets to fill out the load and 1 Tbsp of soap for a final burnish. Refill: Harbor Freight Tumbler Refill Kit, also sold as a 2-kit pack.
| Model | Barrel | Coarse 60/90 | Medium 220 | Pre-polish | Polish |
|---|---|---|---|---|---|
| 3 lb single drum (67631), dual drum (67632, each barrel) | 3 lb | 4 Tbsp | 4 Tbsp | 6 Tbsp | 6 Tbsp |
National Geographic
National Geographic tumblers come with one pre-portioned pack of grit for each step, so the instructions don’t give a measured amount. Their bulk grit kit includes a 10 mL scoop. Fill the barrel 2/3 to 3/4 full and add water until it almost covers the rocks. For a 2 to 3 lb barrel, about 1 to 2 level tablespoons per pound of rock is a good starting point. Refill: National Geographic Tumbler Refill Kit.
| Step | Grit | Suggested time | Speed (3 lb Professional) |
|---|---|---|---|
| 1. Coarse | 60/90 silicon carbide | 3 to 5 days | 3 (fastest) |
| 2. Medium | 120/220 silicon carbide | 6 to 8 days | 2 |
| 3. Pre-polish | 500 aluminum oxide | 6 to 8 days | 1 (slowest) |
| 4. Polish | Aluminum oxide | 7 to 10 days | 1 (slowest) |
Smithsonian
The Smithsonian Rock Tumbler uses a three-step process with one pre-measured bag of grit per step for a 1/2 lb load of stones. Never fill the barrel more than 3/4 full. Add water to just cover the stones for the grit steps and to just under the stones for the polish. Refill: Smithsonian Tumbler Refill.
| Step | Amount | Suggested time |
|---|---|---|
| 1. Coarse grit | 1 bag | 2 to 4 days |
| 2. Medium grit | 1 bag | 12 to 14 days |
| 3. Polish | 1 bag | 7 to 8 days |
Comparing the brands
- Per pound of rock, the published charts work out to about 1.3 tablespoons of coarse and medium grit and up to 2 tablespoons of pre-polish and polish.
- Weight and volume: a cup of grit weighs roughly a pound, so 1 level tablespoon is about 1 ounce. By that measure, Thumler’s 4 oz for a 3 lb barrel is close to the 4 tablespoons Lortone and Harbor Freight use.
- Pre-polish and polish: Lortone and Harbor Freight use a little more than the coarse grit; Thumler’s uses half as much. Thorough cleaning between steps matters more than the exact amount.
For what each step does, read grit stages or the four-step guide. Not sure which grit fits your tumbler? Find your tumbler refill or ask us.
Sources: Lortone 45C, 33B and 3-1.5B instructions (2008); Thumler’s rotary tumbler instruction sheet; Harbor Freight Chicago Electric 67631 manual; National Geographic 3 lb Professional Rock Tumbler and grit refill kit manuals; Smithsonian Rock Tumbler (NSI #6354) manual. Always follow the instructions that came with your own tumbler if they differ.