# Spoked flywheels Ø50 to Ø150 × 10

> What size flywheel does a small Stirling engine need?

- Category: Stirling engines › Drives & mechanisms
- Kind: Hardware
- Basis: Rim Ø D × 10, five spokes 5 wide, Ø5 (Ø50) or Ø8 bore, radial M3 tapped hole
- Page: https://xemstudio.com/objects/spoked-flywheels/ · JSON: https://xemstudio.com/api/geometry?object=spoked-flywheels · Plain text: https://xemstudio.com/objects/spoked-flywheels/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 Ø D × 10 wheel with five 5 mm spokes and a Ø5 (Ø50 wheel) or Ø8 (Ø80–150) bore; a radial Ø2.5 hole (M3 tap drill) at mid-thickness locks it to the shaft.
- Between the spokes the wheel is hollow inside: the band from 0.18 D radius to 8 mm inside the rim is a closed void with 1.5 mm faces on both sides.
- On the Ø80–Ø150 files the spoke ends stand proud of the rim; the overall size is in the table.
- Energy stored at a given speed goes with the fourth power of diameter, so diameter does more than thickness.

## 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 |
|---|---|---|---|---|
| flywheel bore | Ø5 / Ø8 | crankshaft (M3 set screw) | slide | flywheel-* |
| flywheel set-screw hole | Ø2.5 | M3 tap drill | designed | flywheel-* |

## Sizes

| file | rim Ø | thickness | bore | overall (spoke ends) |
|---|---|---|---|---|
| flywheel-50 | 50 | 10 | 5 | 50 × 50 |
| flywheel-80 | 80 | 10 | 8 | 83.6 × 84.5 |
| flywheel-100 | 100 | 10 | 8 | 106.0 × 108.1 |
| flywheel-120 | 120 | 10 | 8 | 128.4 × 131.7 |
| flywheel-150 | 150 | 10 | 8 | 162.0 × 167.0 |

## Where the files are

- Wikipedia: [Crank (mechanism)](https://en.wikipedia.org/wiki/Crank_(mechanism)) — web — CC BY-SA 4.0 (text)
- Wikipedia: [Flywheel](https://en.wikipedia.org/wiki/Flywheel) — web — CC BY-SA 4.0 (text)
- Wikipedia: [Stirling engine](https://en.wikipedia.org/wiki/Stirling_engine) — 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 (5 parts, CC BY 4.0, Xem Studio)

Index: https://xemstudio.com/files/hardware/spoked-flywheels/index.json

- flywheel-50: [STEP](https://xemstudio.com/files/hardware/crank-conrod-flywheel-kit/flywheel-50.step) · [STL](https://xemstudio.com/files/hardware/crank-conrod-flywheel-kit/flywheel-50.stl) — spoked flywheel Ø50 × 10 overall: rim 8 wide (ID Ø34), hub Ø18, five spokes 5 wide × 7 thick on the mid-plane, open windows between; Ø5 bore, M3 set screw
- flywheel-80: [STEP](https://xemstudio.com/files/hardware/crank-conrod-flywheel-kit/flywheel-80.step) · [STL](https://xemstudio.com/files/hardware/crank-conrod-flywheel-kit/flywheel-80.stl) — spoked flywheel Ø80 × 10 overall: rim 8 wide (ID Ø64), hub Ø28.8, five spokes 5 wide × 7 thick on the mid-plane, open windows between; Ø8 bore, M3 set screw
- flywheel-100: [STEP](https://xemstudio.com/files/hardware/crank-conrod-flywheel-kit/flywheel-100.step) · [STL](https://xemstudio.com/files/hardware/crank-conrod-flywheel-kit/flywheel-100.stl) — spoked flywheel Ø100 × 10 overall: rim 8 wide (ID Ø84), hub Ø36, five spokes 5 wide × 7 thick on the mid-plane, open windows between; Ø8 bore, M3 set screw
- flywheel-120: [STEP](https://xemstudio.com/files/hardware/crank-conrod-flywheel-kit/flywheel-120.step) · [STL](https://xemstudio.com/files/hardware/crank-conrod-flywheel-kit/flywheel-120.stl) — spoked flywheel Ø120 × 10 overall: rim 8 wide (ID Ø104), hub Ø43.2, five spokes 5 wide × 7 thick on the mid-plane, open windows between; Ø8 bore, M3 set screw
- flywheel-150: [STEP](https://xemstudio.com/files/hardware/crank-conrod-flywheel-kit/flywheel-150.step) · [STL](https://xemstudio.com/files/hardware/crank-conrod-flywheel-kit/flywheel-150.stl) — spoked flywheel Ø150 × 10 overall: rim 8 wide (ID Ø134), hub Ø54, five spokes 5 wide × 7 thick on the mid-plane, open windows between; Ø8 bore, M3 set screw

## How it fits

### Goes in or on
- [Crankshafts Ø3, Ø5 and Ø8 with full-length D-flat](https://xemstudio.com/objects/stirling-crankshafts/): Ø5 / Ø8 bore, M3 grub on the flat

### Connects to
- [Shaft adapter Ø5 to Ø8 × 20](https://xemstudio.com/objects/shaft-adapter-5-to-8mm/): Ø8 bore on a Ø5 shaft
- [Bolt-on counterweight arcs R15, R20 and R25](https://xemstudio.com/objects/bolt-on-counterweights/): arc bolted opposite the crank pin

### Alternatives
- [Flywheels Ø100–Ø200 with hex-nut rim pockets](https://xemstudio.com/objects/nut-pocket-flywheels/): rim pockets carry hex nuts

## Questions

**How big a flywheel for a 2 in tri-clamp engine?**

The 2 in engines run Ø100 × 10 on an Ø8 shaft.

**What bore are the spoked flywheels?**

Ø5 on the Ø50, Ø8 on the Ø80–150; the 5 → 8 shaft adapter puts an Ø8 wheel on a Ø5 shaft.

## Fits with

- [Flywheels Ø100–Ø200 with hex-nut rim pockets](https://xemstudio.com/objects/nut-pocket-flywheels/)
- [Shaft adapter Ø5 to Ø8 × 20](https://xemstudio.com/objects/shaft-adapter-5-to-8mm/)
- [Crankshafts Ø3, Ø5 and Ø8 with full-length D-flat](https://xemstudio.com/objects/stirling-crankshafts/)
- [Bolt-on counterweight arcs R15, R20 and R25](https://xemstudio.com/objects/bolt-on-counterweights/)