# National Geographic rock tumbler: grit amounts, times and speed settings

Source: https://tumblegrit.com/blog/national-geographic-rock-tumbler-instructions
Published: 2026-10-01
Publisher: Tumble Grit

**Short answer:** Use the four numbered grits in order, one per step: grit 1 for 3 to 5 days, grit 2 for 6 to 8 days, grit 3 for 6 to 8 days and grit 4 for 7 to 10 days, the ranges the Hobby manual suggests. Fill the barrel 1/2 to 2/3 full and add water to the top of the rocks. On 3-speed models run speed 3 for grit 1, speed 2 for grit 2 and speed 1 for grits 3 and 4.

This page is for owners who lost the booklet, or followed it and got dull stones. Tumble Grit is independent and not affiliated with National Geographic or the maker of the kits, and this is not a copy of the manual. The model facts come from the maker's listings and the published manual. The rest is standard rotary tumbling practice. Three things decide the result: how long step 1 runs, how clean the barrel is between steps, and how the polish step is loaded.

## Which National Geographic rock tumbler do you have?

The kits share one grit system, numbered 1 to 4, but differ in barrel size, timer and speed control. Find your model in the table, then use the matching rows in the rest of this page. Barrel size matters most: it sets how much rock and grit go in.

| Model | Barrel | Timer | Speed |
| --- | --- | --- | --- |
| Hobby | 1 lb | Up to 7 days | No speed setting in the manual |
| Professional | 2 lb | Hours and days, up to 12 days on the current version | 3 speeds |
| 3 lb kit | 3 lb | Up to 9 days | 3 speeds |

From maker and retailer listings checked in October 2026. Versions change, so the keypad on your own machine is the final word.

Note: Tumble Grit is not affiliated with National Geographic or the maker of the kits. If your booklet and this page disagree on a model detail, follow the booklet.

## National Geographic rock tumbler grit times and speed by step

The days below are the ranges the published Hobby manual suggests. The speed column applies to the 3-speed models and follows their manual as it appears on manual archive sites. Confirm it against your booklet if you still have it.

In step 1 these times are shorter than standard hobby practice, where one run is **7 days** and hard, jagged rough often needs 2 to 4 runs. Longer step 1 runs give better shape. The [grit chart](https://tumblegrit.com/blog/rock-tumbling-grit-chart) shows the standard schedule for comparison.

| Step | Packet | Days | Speed (3-speed models) | Job |
| --- | --- | --- | --- | --- |
| 1 | Grit 1, coarse | 3 to 5 | 3, fastest | Shapes and rounds the rough |
| 2 | Grit 2, medium | 6 to 8 | 2 | Removes coarse scratches |
| 3 | Grit 3, pre-polish | 6 to 8 | 1, slowest | Leaves a satin surface |
| 4 | Grit 4, polish | 7 to 10 | 1, slowest | Brings the shine |

Manual ranges for the kit grits. Step 1 can be repeated with fresh coarse grit until the stones are shaped.

## How much grit for a National Geographic rock tumbler?

The kit packets are portioned for the barrel they ship with: one packet of the numbered grit per step, for one load. The number of packets in the box differs by kit version, so count yours before you start.

When the packets run out, measure loose grit: about **2 level tablespoons per pound of rock**, the same in all four steps. A barrel's rating counts rock, water and grit together, so a 1 lb barrel holds well under a pound of rock. The [grit calculator](https://tumblegrit.com/tools/rock-tumbler-grit-calculator) gives the amount for any load.

| Barrel | Rock in a correct fill | Loose grit per step |
| --- | --- | --- |
| 1 lb | About 1/2 to 3/4 lb | 1 to 1.5 tablespoons |
| 2 lb | About 1 to 1.5 lb | 2 to 3 tablespoons |
| 3 lb | About 2 lb | About 4 tablespoons |

Loose grit per step at the standard rate. Count ceramic media as rock.

[See grit refills for these barrels](https://tumblegrit.com/best/best-national-geographic-tumbler-grit-refill)

## How to use the National Geographic rock tumbler, step by step

The same routine repeats four times with a different grit. Only step 1 changes the shape of the stones. Each later step only removes the scratches left by the step before, so nothing is gained by rushing ahead.

1. Load rocks of one hardness in mixed sizes until the barrel is 1/2 to 2/3 full. If the rocks do not reach half, top up with ceramic media.
2. Add grit 1: one kit packet, or 2 level tablespoons of coarse grit (step 1, 60/90) per pound of rock. Add water until it reaches the top layer of rocks, no higher.
3. Wipe the rim and lid seal clean, close the barrel firmly, set 3 to 5 days on the timer and choose speed 3 on a 3-speed model.
4. When the timer stops, open the barrel carefully, pointed away from you. Pour the load through the strainer over a bucket, never over the sink.
5. Rinse the stones, barrel, lid and seal until no grit is left. If any stone still has pits, cracks or flat broken faces, run step 1 again for up to 7 days with fresh coarse grit.
6. Repeat with grit 2 for 6 to 8 days at speed 2, then grit 3 for 6 to 8 days at speed 1. Clean everything after each step.
7. Run grit 4, the polish, for 7 to 10 days at speed 1. On a model with a 7 day timer, start the timer again when it stops.
8. Rinse the stones and let them dry. For extra shine, burnish with about half a tablespoon of grated bar soap per pound of rock for 1 hour to 1 day.

Note: Some kits include a finishing foam for use after grit 4. It is specific to the kit, so follow the directions printed on that product.

## How to tell each step is done

Judge the stones dry and in good light. Wet stones always look shiny, which hides scratches. Rinse a few, dry them with a towel and compare them with the signs below before you open the next packet.

- Step 1 is done when every stone is rounded, with no pits, cracks or flat broken faces. This is the step that most often needs a second run.
- Step 2 is done when the stones are smooth and evenly matte, with no coarse scratches left.
- Step 3 is done when dry stones look satin and feel silky in the hand.
- Step 4 is done when dry stones shine. If they are still dull after 10 days, more polish time will not fix it: go back to grit 3.

## National Geographic rock tumbler tips: three changes for shinier stones

Dull stones from a kit tumbler usually trace back to the same three habits. None of them needs a new machine. The page on [why tumbled rocks are not shiny](https://tumblegrit.com/blog/why-tumbled-rocks-are-not-shiny) covers the rarer causes.

- Longer step 1: run coarse grit for 7 days at a time and repeat until every stone is shaped. One kit packet covers one run, so repeats need a coarse grit refill.
- More cleaning: one grain of coarse grit in the polish scratches the whole batch. Rinse stones, barrel, lid and lid seal between steps, and send the mud to a bucket as described in [how to dispose of slurry](https://tumblegrit.com/blog/how-to-dispose-of-rock-tumbling-slurry).
- A better polish step: stones shrink through the steps, so top the barrel back up to at least half with ceramic media, give polish the full 7 to 10 days, and use a fresh aluminum oxide polish when the kit packet is gone.

## Which speed setting to use and when to slow down

A faster barrel grinds harder and also knocks the stones together harder. That suits step 1 on tough rock such as agate and jasper, which is why the 3-speed manual puts grit 1 on speed 3. The finer steps only smooth the surface, so they run slower to avoid fresh chips.

Brittle material such as obsidian and glass chips easily. Run it on the slowest speed in every step, keep the barrel closer to 2/3 full and add cushioning media. The [speed chart](https://tumblegrit.com/blog/rock-tumbler-speed-chart) lists barrel speeds by size and stage for other machines.

## Quick answers

Short answers to the most common questions about these kits. Model details come from listings, so check your own booklet where it differs.

- **How much grit for a National Geographic rock tumbler?** One numbered packet per step for the kit load. With loose grit, use about 2 level tablespoons per pound of rock.
- **What are the National Geographic rock tumbler grit times?** The Hobby manual suggests 3 to 5 days for grit 1, 6 to 8 days for grits 2 and 3, and 7 to 10 days for grit 4.
- **Is this the rock tumbler instructions PDF?** No. This is an independent how-to, not a copy of the manual. The booklet for your exact model is the final word on its controls.
- **How do you use the Hobby edition rock tumbler?** Fill the 1 lb barrel 1/2 to 2/3 full, add one grit and water, and set the days on the keypad. The timer runs up to 7 days.
- **Which speed goes with which grit?** On 3-speed models: speed 3 for grit 1, speed 2 for grit 2, speed 1 for grits 3 and 4.

## Gear guides for this topic

- https://tumblegrit.com/best/best-national-geographic-tumbler-grit-refill
- https://tumblegrit.com/best/best-coarse-rock-tumbler-grit
- https://tumblegrit.com/best/best-rock-tumbling-polish
- https://tumblegrit.com/best/best-ceramic-tumbling-media

## Sources

- [Blue Marble: Choosing a National Geographic Rock Tumbler](https://thinkbluemarble.com/learning-galaxy/product-zone/choosing-a-national-geographic-rock-tumbler/)
- [Blue Marble: National Geographic Professional Rock Tumbler Kit](https://thinkbluemarble.com/product/national-geographic-professional-rock-tumbler-kit/)
- [ManualsLib: National Geographic Hobby Tumbler manual](https://www.manualslib.com/manual/3620309/National-Geographic-Hobby-Tumbler.html)