# Ground rods, hollow piston rod and crank shafts for the performance engines (Ø6, Ø8, Ø10 / 7)

> What rods and shafts does a tri-clamp crosshead Stirling engine need?

- Category: Hardware › Stirling & thermoacoustic
- Kind: Hardware
- Basis: Design values; lengths from the engines' layouts
- Page: https://xemstudio.com/objects/stirling-precision-rods/ · JSON: https://xemstudio.com/api/geometry?object=stirling-precision-rods · Plain text: https://xemstudio.com/objects/stirling-precision-rods/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

- Ground rods cut to length with threaded ends (threads drawn at the major diameter): the displacer rods (Ø6, M6), the gamma's piston rod (Ø8, M8), the beta's hollow piston rod (Ø10 / Ø7, M10 × 1; the displacer rod runs inside it) and the Ø8 crank shafts the built-up cranks are pressed onto.

## 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 |
|---|---|---|---|---|
| displacer rods | Ø6, M6 × 12 ends | gland bushings (run), cap and yoke M6 holes | run | rod-6x* |
| piston rod | Ø8, M8 × 12 ends | gland bushings 8 × 12 × 20 (run) | run | rod-8x* |
| hollow rod | Ø10 / Ø7, M10 × 1 × 16 ends | guide bushings 10 × 14 × 15 (run); Ø6 displacer rod inside (no contact) | run | tube-10x7* |
| crank shafts | Ø8 | crank webs (press), 608 bores, collars, flywheel, pulley | press | shaft-8x* |
| transfer tube | Ø12.7 × 0.89 | 1/2 in tube compression fittings | designed | transfer-tube* |

## Sizes

| part | size |
|---|---|
| rod-6x423.2-m6 | Ø6 × 423.20 |
| rod-8x304.85-m8 | Ø8 × 304.85 |
| rod-6x300.25-m6 | Ø6 × 300.25 |
| tube-10x7x158.6-m10x1 | Ø10/7 × 158.60 |
| shaft-8x56.5 | Ø8 × 56.50 |
| shaft-8x88 | Ø8 × 88.00 |
| shaft-8x46.3 | Ø8 × 46.30 |
| shaft-8x103.95 | Ø8 × 103.95 |
| shaft-8x138.3 | Ø8 × 138.30 |

## Where the files are

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

## Free STEP/STL (13 parts, CC BY 4.0, Xem Studio)

Index: https://xemstudio.com/files/hardware/stirling-precision-rods/index.json

- rod-6x423.2-m6: [STEP](https://xemstudio.com/files/hardware/stirling-precision-rods/rod-6x423.2-m6.step) · [STL](https://xemstudio.com/files/hardware/stirling-precision-rods/rod-6x423.2-m6.stl) — Ø6 × 423.20 ground rod: horizontal gamma displacer rod, M6 × 12 both ends (drawn at Ø6)
- rod-8x304.85-m8: [STEP](https://xemstudio.com/files/hardware/stirling-precision-rods/rod-8x304.85-m8.step) · [STL](https://xemstudio.com/files/hardware/stirling-precision-rods/rod-8x304.85-m8.stl) — Ø8 × 304.85 ground rod: horizontal gamma piston rod, M8 × 12 both ends
- rod-6x300.25-m6: [STEP](https://xemstudio.com/files/hardware/stirling-precision-rods/rod-6x300.25-m6.step) · [STL](https://xemstudio.com/files/hardware/stirling-precision-rods/rod-6x300.25-m6.stl) — Ø6 × 300.25 ground rod: charged beta displacer rod, M6 × 12 both ends
- rod-6x315.4-m6: [STEP](https://xemstudio.com/files/hardware/stirling-precision-rods/rod-6x315.4-m6.step) · [STL](https://xemstudio.com/files/hardware/stirling-precision-rods/rod-6x315.4-m6.stl) — Ø6 × 315.40 ground rod: walking-beam gamma displacer rod, M6 × 12 both ends
- transfer-tube-12.7x0.89x64: [STEP](https://xemstudio.com/files/hardware/stirling-precision-rods/transfer-tube-12.7x0.89x64.step) · [STL](https://xemstudio.com/files/hardware/stirling-precision-rods/transfer-tube-12.7x0.89x64.stl) — transfer tube Ø12.7 × 0.89 wall × 64 (1/2 in tube) between the two 1/2 NPT fittings
- tube-10x7x158.6-m10x1: [STEP](https://xemstudio.com/files/hardware/stirling-precision-rods/tube-10x7x158.6-m10x1.step) · [STL](https://xemstudio.com/files/hardware/stirling-precision-rods/tube-10x7x158.6-m10x1.stl) — hollow piston rod Ø10 / Ø7 × 158.60, M10 × 1 × 16 both ends (drawn at Ø10)
- shaft-8x56.5: [STEP](https://xemstudio.com/files/hardware/stirling-precision-rods/shaft-8x56.5.step) · [STL](https://xemstudio.com/files/hardware/stirling-precision-rods/shaft-8x56.5.stl) — Ø8 × 56.50 crank shaft (pressed into the webs)
- shaft-8x88: [STEP](https://xemstudio.com/files/hardware/stirling-precision-rods/shaft-8x88.step) · [STL](https://xemstudio.com/files/hardware/stirling-precision-rods/shaft-8x88.stl) — Ø8 × 88.00 crank shaft (pressed into the webs)
- shaft-8x46.3: [STEP](https://xemstudio.com/files/hardware/stirling-precision-rods/shaft-8x46.3.step) · [STL](https://xemstudio.com/files/hardware/stirling-precision-rods/shaft-8x46.3.stl) — Ø8 × 46.30 crank shaft (pressed into the webs)
- shaft-8x103.95: [STEP](https://xemstudio.com/files/hardware/stirling-precision-rods/shaft-8x103.95.step) · [STL](https://xemstudio.com/files/hardware/stirling-precision-rods/shaft-8x103.95.stl) — Ø8 × 103.95 crank shaft (pressed into the webs)
- shaft-8x138.3: [STEP](https://xemstudio.com/files/hardware/stirling-precision-rods/shaft-8x138.3.step) · [STL](https://xemstudio.com/files/hardware/stirling-precision-rods/shaft-8x138.3.stl) — Ø8 × 138.30 crank shaft (pressed into the webs)
- shaft-8x95.8: [STEP](https://xemstudio.com/files/hardware/stirling-precision-rods/shaft-8x95.8.step) · [STL](https://xemstudio.com/files/hardware/stirling-precision-rods/shaft-8x95.8.stl) — Ø8 × 95.80 crank shaft (pressed into the webs)
- shaft-8x91: [STEP](https://xemstudio.com/files/hardware/stirling-precision-rods/shaft-8x91.step) · [STL](https://xemstudio.com/files/hardware/stirling-precision-rods/shaft-8x91.stl) — Ø8 × 91.00 crank shaft (twin: both webs pressed on it)

## Questions

**Why a hollow piston rod?**

In the beta the displacer rod runs inside it, coaxial.

## Fits with

- [Crosshead yokes with a Ø5 stub wrist pin: Ø6, Ø8 and hollow Ø10 rods](https://xemstudio.com/objects/stirling-crosshead-yokes/)
- [Build list: Tri-clamp horizontal gamma generator, 2 in, chargeable](https://xemstudio.com/objects/list-tri-clamp-horizontal-gamma/)
- [Build list: Tri-clamp charged beta, 2 in](https://xemstudio.com/objects/list-tri-clamp-charged-beta/)