# Ratchet wheels Ø40 with 12, 24 and 36 teeth

> How are the teeth of a ratchet wheel shaped?

- Category: Stirling engines › Drives & mechanisms
- Kind: Hardware
- Basis: Sawtooth wheel: tips at R20, roots at R17 (3 mm deep), each tooth rising over 85 % of the pitch and dropping over 15 %
- Page: https://xemstudio.com/objects/ratchet-wheels/ · JSON: https://xemstudio.com/api/geometry?object=ratchet-wheels · Plain text: https://xemstudio.com/objects/ratchet-wheels/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); linked files under their publishers' licenses

**Exact dimensions.** Every file is drawn at true size with no printing tolerance. The holes and pins that meet another part are listed below under Mating features, with the fit each joint needs; open those by your printer's or process's clearance before making the part.

## Notes

- A Ø40 × 6 wheel with a Ø5 bore and 12, 24 or 36 sawtooth teeth 3 mm deep (tips on R20, roots on R17).
- Each tooth rises from root to tip over 85 % of the pitch (the back) and drops back over 15 % (the face the pawl locks against).
- Steps: 12 teeth 30°, 24 teeth 15°, 36 teeth 10°. Fewer teeth are larger and stronger.
- A one-way drive: anti-reverse on a reel, a hand-wound starter, or between a Stirling flywheel and a generator so the generator never back-drives the engine.

## Mating features (exact size; open press / slide / run / socket by your process clearance, leave designed and clamp as drawn)

| feature | exact | mates with | fit | files |
|---|---|---|---|---|
| wheel bore | Ø5 | Ø5 shaft | slide | ratchet-* |

## Sizes

| file | teeth | step | tip Ø | root Ø | thickness | bore |
|---|---|---|---|---|---|---|
| ratchet-12t-d40 | 12 | 30° | 40 | 34 | 6 | 5 |
| ratchet-24t-d40 | 24 | 15° | 40 | 34 | 6 | 5 |
| ratchet-36t-d40 | 36 | 10° | 40 | 34 | 6 | 5 |

## Where the files are

- Wikipedia: [Ratchet (device)](https://en.wikipedia.org/wiki/Ratchet_(device)) — web — CC BY-SA 4.0 (text)
- Wikipedia: [Pawl](https://en.wikipedia.org/wiki/Pawl) — web — CC BY-SA 4.0 (text)
- Long Earth Society: [Engine builds that use these parts (videos and write-ups)](https://longearthsociety.com/engineering/) — web, video — LES site

## Free STEP/STL (3 parts, CC BY 4.0, Xem Studio)

Index: https://xemstudio.com/files/hardware/ratchet-wheels/index.json

- ratchet-12t-d40: [STEP](https://xemstudio.com/files/hardware/ratchet-and-pawl/ratchet-12t-d40.step) · [STL](https://xemstudio.com/files/hardware/ratchet-and-pawl/ratchet-12t-d40.stl) — ratchet wheel Ø40 × 6, 12 teeth 3 mm deep, Ø5 bore
- ratchet-24t-d40: [STEP](https://xemstudio.com/files/hardware/ratchet-and-pawl/ratchet-24t-d40.step) · [STL](https://xemstudio.com/files/hardware/ratchet-and-pawl/ratchet-24t-d40.stl) — ratchet wheel Ø40 × 6, 24 teeth 3 mm deep, Ø5 bore
- ratchet-36t-d40: [STEP](https://xemstudio.com/files/hardware/ratchet-and-pawl/ratchet-36t-d40.step) · [STL](https://xemstudio.com/files/hardware/ratchet-and-pawl/ratchet-36t-d40.stl) — ratchet wheel Ø40 × 6, 36 teeth 3 mm deep, Ø5 bore

## How it fits

### Goes in or on
- [Metric shafts Ø3 to Ø10 with D-flats and clip grooves](https://xemstudio.com/objects/metric-shafts/): Ø5 shaft in the bore

### Connects to
- [Pawl 24 mm with a Ø3 pivot for the Ø40 ratchet wheels](https://xemstudio.com/objects/ratchet-pawl/): pawl tip against the tooth face

### Also needed
- [Torsion spring wire Ø0.8, OD 8, 6 coils](https://xemstudio.com/objects/torsion-spring/): holds the pawl on the teeth

## Questions

**How many teeth should a ratchet have?**

12 teeth (30° steps) are the largest and strongest; 24 or 36 give 15° or 10° steps.

**How deep are the teeth?**

3 mm, from R20 at the tips to R17 at the roots.

## Fits with

- [Pawl 24 mm with a Ø3 pivot for the Ø40 ratchet wheels](https://xemstudio.com/objects/ratchet-pawl/)
- [Metric shafts Ø3 to Ø10 with D-flats and clip grooves](https://xemstudio.com/objects/metric-shafts/)
- [Spur gears, involute 20°: module 0.5, 1 and 2, 12–60 teeth](https://xemstudio.com/objects/spur-gears-involute/)
- [Torsion spring wire Ø0.8, OD 8, 6 coils](https://xemstudio.com/objects/torsion-spring/)