# Inner crank webs for the tri-clamp cross gamma: two throws 90° apart on a Ø3 shaft

> How do I make a two-throw crank at 90° that fits inside a 2 inch tri-clamp cross?

- Category: Hardware › Stirling & thermoacoustic
- Kind: Hardware
- Basis: Design values: 6 mm throws (12 mm strokes), Ø3 pins and shaft, 623 con-rod eyes (R7)
- Page: https://xemstudio.com/objects/tri-clamp-cross-crank-webs/ · JSON: https://xemstudio.com/api/geometry?object=tri-clamp-cross-crank-webs · Plain text: https://xemstudio.com/objects/tri-clamp-cross-crank-webs/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 built-up crank small enough to turn inside a Ø29 chamber in the middle of the cross. The hub web goes on the end of the Ø3 shaft (M3 grub); a Ø3 × 12 dowel pressed through its disc is the diaphragm crank pin; the con-rod for the diaphragm turns on it; the link web is pressed on the pin's far end.
- The link web carries the displacer pin, a second Ø3 × 12 dowel, 90° on from the diaphragm pin. Each pin passes only through its own con-rod: the shaft stops in the hub web, the diaphragm pin stops in the link web, the displacer pin starts there, so no con-rod eye ever meets another pin.
- Both throws are 6 mm. The con-rod eyes sweep a radius of 13; the webs are Ø20.

## 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 |
|---|---|---|---|---|
| shaft bore | Ø3 | Ø3 crankshaft (M3 grub) | slide | inner-crank-web-hub-* |
| grub hole | Ø2.5 (M3 tapped) | set-m3x3 | designed | inner-crank-web-hub-* |
| crank-pin holes | Ø3 at r 6 (link web: two, 90° apart) | dowel-3x12 crank pins | press | all |
| throw | 6 (12 mm strokes), displacer pin 90° on | conrod-30 eyes (623) | designed | all |

## Sizes

| file | hub_mm | disc_mm | pins |
|---|---|---|---|
| inner-crank-web-hub-r6 | Ø10 × 6, Ø3 bore, M3 grub | Ø20 × 4 | 1 at r 6 |
| inner-crank-web-link-r6 |  | Ø20 × 5.5 | 2 at r 6, 90° apart |

## 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-cross-crank-webs/index.json

- inner-crank-web-hub-r6: [STEP](https://xemstudio.com/files/hardware/tri-clamp-cross-crank-webs/inner-crank-web-hub-r6.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-cross-crank-webs/inner-crank-web-hub-r6.stl) — hub web: Ø10 × 6 hub with Ø3 shaft bore and M3 grub hole (Ø2.5), Ø20 × 4 disc with the Ø3 crank-pin hole at r 6
- inner-crank-web-link-r6: [STEP](https://xemstudio.com/files/hardware/tri-clamp-cross-crank-webs/inner-crank-web-link-r6.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-cross-crank-webs/inner-crank-web-link-r6.stl) — link web: Ø20 × 5.5 disc, Ø3 pin holes at r 6, 90° apart

## Questions

**Which way does it turn?**

So that the displacer pin is a quarter turn ahead of the diaphragm pin: the build list states the direction.

**How is the link web held?**

Pressed on the diaphragm pin, which is pressed in the hub web; the displacer pin is pressed in the link web.

## Fits with

- [Tri-clamp bearing cap: 2 in cap with a long Ø3 shaft bore and two 623 seats](https://xemstudio.com/objects/tri-clamp-bearing-cap/)
- [Crankcase insert for a 2 in tri-clamp cross: displacer-rod guide, crank chamber and run filler](https://xemstudio.com/objects/tri-clamp-cross-crankcase-insert/)
- [Connecting rods 30 to 80 mm centres with 623 pockets](https://xemstudio.com/objects/connecting-rods-623/)
- [Dowel pins, 2–6 mm (ISO 2338 / DIN 6325)](https://xemstudio.com/objects/dowel-pins-metric/)
- [Build list: Tri-clamp cross diaphragm gamma, 2 in](https://xemstudio.com/objects/list-tri-clamp-cross-diaphragm-gamma/)