# Link webs: a second crank throw on the first crank pin

> How do I put two crank pins at different angles on one overhung crank?

- Category: Hardware › Stirling & thermoacoustic
- Kind: Hardware
- Basis: Design values (pin radii and angles set by the engines' kinematics); Ø3 dowel pins (ISO 8734)
- Page: https://xemstudio.com/objects/tri-clamp-rd-link-webs/ · JSON: https://xemstudio.com/api/geometry?object=tri-clamp-rd-link-webs · Plain text: https://xemstudio.com/objects/tri-clamp-rd-link-webs/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

- The web is pressed on crank pin 1 (which is pressed in the crank disc) and carries crank pin 2. The power con-rod runs on pin 1 between the disc and the web; the displacer drive runs on pin 2 outside the web. The shaft ends at the disc, so nothing crosses the con-rods' path.
- Beta web: pin 2 at the same 10 mm radius, 90° from pin 1. Gamma web: pin 2 at 7 mm, 45° from pin 1; with the bell crank's own lag the displacer leads the power piston's volume by close to a quarter turn.
- Turn the web over to swap which way pin 2 leads: the web is the same both ways.

## 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 |
|---|---|---|---|---|
| pin holes | Ø3 (two) | Ø3 crank pins (dowels) | press | all |

## Sizes

| part | pin1_radius_mm | pin2_radius_mm | angle_deg | thickness_mm |
|---|---|---|---|---|
| rd-link-web-r10-90 | 10.0 | 10.0 | 90.0 | 14.0 |
| rd-link-web-r7-45 | 10.0 | 7.0 | 45.0 | 14.0 |

## Where the files are

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

## Free STEP/STL (2 parts, CC BY 4.0, Xem Studio)

Index: https://xemstudio.com/files/hardware/tri-clamp-rd-link-webs/index.json

- rd-link-web-r10-90: [STEP](https://xemstudio.com/files/hardware/tri-clamp-rd-link-webs/rd-link-web-r10-90.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-rd-link-webs/rd-link-web-r10-90.stl) — link web 14 thick: Ø3 press holes for crank pin 1 (radius 10) and pin 2 (radius 10) 90° apart about the shaft axis, Ø12 ends
- rd-link-web-r7-45: [STEP](https://xemstudio.com/files/hardware/tri-clamp-rd-link-webs/rd-link-web-r7-45.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-rd-link-webs/rd-link-web-r7-45.stl) — link web 14 thick: Ø3 press holes for crank pin 1 (radius 10) and pin 2 (radius 7) 45° apart about the shaft axis, Ø12 ends

## Questions

**Which way does the engine turn?**

The way that makes the displacer lead the power piston; turning the web over reverses it.

## Fits with

- [Counterweighted crank discs, Ø5 bore, 10 to 30 mm stroke](https://xemstudio.com/objects/counterweighted-crank-discs/)
- [Tri-clamp rolling-diaphragm power head, 2 in: standard clamp face, cylinder, rod guide and crank tower, with its diaphragm seat ring](https://xemstudio.com/objects/tri-clamp-rd-power-head/)
- [Build list: Tri-clamp rolling-diaphragm beta, 2 in](https://xemstudio.com/objects/list-tri-clamp-rd-beta/)
- [Build list: Tri-clamp rolling-diaphragm gamma, 2 in](https://xemstudio.com/objects/list-tri-clamp-rd-gamma/)