# Rocking link 170 mm (crank to rocker)

> What rocks the test tube of a marble Stirling engine?

- Category: Hardware › Stirling & thermoacoustic
- Kind: Hardware
- Basis: My geometry: same section as the pin-end con-rods (8 × 5, Ø3 ends)
- Page: https://xemstudio.com/objects/marble-engine-rocking-link/ · JSON: https://xemstudio.com/api/geometry?object=marble-engine-rocking-link · Plain text: https://xemstudio.com/objects/marble-engine-rocking-link/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

- 170 mm between Ø3 holes; from the crank pin that leads the power pin by 90° to the rocker's lever pin. Length chosen so the rocker's mean angle is level.

## 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 |
|---|---|---|---|---|
| end holes | Ø3 | dowel-3x12 crank pin and lever pin (turn in them) | run | all |

## Sizes

| feature | value_mm |
|---|---|
| centres | 170.0 |
| section | 8 × 5 |
| holes | Ø3 |

## 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/marble-engine-rocking-link/index.json

- rocking-link-170: [STEP](https://xemstudio.com/files/hardware/marble-engine-rocking-link/rocking-link-170.step) · [STL](https://xemstudio.com/files/hardware/marble-engine-rocking-link/rocking-link-170.stl) — rocking link, 170 mm centres, Ø3 holes, 8 wide × 5 thick: crank pin to the rocker's lever pin

## Questions

**Why 170 mm?**

It reaches from the crank to the rocker's lever pin 45 below the pivot, so the 7.5 mm crank throw rocks the tube -7.9° to +7.9°, and it sets the crank where the plunger never bottoms.

## Fits with

- [Build list: Test-tube marble engine](https://xemstudio.com/objects/list-test-tube-marble-engine/)
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