# Ø400 flywheel on a Ø12 shaft

> How big a flywheel does a slow large Stirling engine need?

- Category: Stirling engines › Tri-clamp engine parts
- Kind: Hardware
- Basis: Exact geometry
- Page: https://xemstudio.com/objects/htd-flywheel-400/ · JSON: https://xemstudio.com/api/geometry?object=htd-flywheel-400 · Plain text: https://xemstudio.com/objects/htd-flywheel-400/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); linked files under their publishers' licenses
- Use in every chat: add https://xemstudio.com/mcp as a connector (https://xemstudio.com/use-with-ai/)

**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

- Rim r 175..200 × 30 wide, 5 web, Ø50 × 40 hub, two M6 grubs. J = 0.104 kg·m² (3.9 kg) at 2.7 g/cm³, 0.305 kg·m² (11.3 kg) at 7.9 g/cm³.
- On the HTD it hangs outside the seal cap at x 186.5..226.5; a slow flat engine needs the inertia (the speed swing is on the list page).

## 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 |
|---|---|---|---|---|
| bore | Ø12 × 40 | Ø12 shaft, two M6 grubs (drawn Ø6) | slide | all |

## Sizes

| od_mm | rim_mm | web_mm | hub_mm | J_kgm2_2.7 | J_kgm2_7.9 |
|---|---|---|---|---|---|
| 400.0 | 175–200 × 30 | 5.0 | Ø50 × 40 | 0.104 | 0.305 |

## Where the files are

- Long Earth Society: [Engine builds](https://longearthsociety.com/engineering/) — web, video — LES site

## Free STEP/STL (1 parts, CC BY 4.0, Xem Studio)

Index: https://xemstudio.com/files/hardware/htd-flywheel-400/index.json

- flywheel-400-b12: [STEP](https://xemstudio.com/files/hardware/htd-flywheel-400/flywheel-400-b12.step) · [STL](https://xemstudio.com/files/hardware/htd-flywheel-400/flywheel-400-b12.stl) — Ø400 flywheel: rim r 175..200 × 30, web 5, hub Ø50 × 40, Ø12 bore, two M6 tapped radial holes

## Questions

**How heavy is it?**

3.9 kg at 2.7 g/cm³, 11.3 kg at 7.9 g/cm³.

## Fits with

- [Build list: HTD engine, 10 in tri-clamp (high-temperature-differential flat engine)](https://xemstudio.com/objects/list-htd-10in/)
- [HTD generator drive: 210 T crank gear and a 2208 bracket (14 : 1)](https://xemstudio.com/objects/htd-generator-drive/)