# Flexure hub washer: Ø12 to Ø26.4 × 2 mm

> What goes between the hubs in a flexure bearing stack?

- Category: Stirling engines › Free-piston
- Kind: Hardware
- Basis: Washer = the leaf hub: Ø hub × leaf bore, 2 mm thick, the same as the rim spacer
- Page: https://xemstudio.com/objects/flexure-hub-clamp-washer/ · JSON: https://xemstudio.com/api/geometry?object=flexure-hub-clamp-washer · Plain text: https://xemstudio.com/objects/flexure-hub-clamp-washer/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 2 mm washer the size of a leaf's hub, with the leaf's bore, that sits between the two leaf hubs of a stack: as thick as the 2 mm rim spacer between the leaf rims, so both leaves stay flat and parallel.
- Ø12 × Ø4, Ø13.2 × Ø5, Ø17.6 × Ø5, Ø22 × Ø8, Ø26.4 × Ø8 for the Ø40 to Ø120 leaves.

## 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 |
|---|---|---|---|---|
| hub-clamp bore | Ø4 / Ø5 / Ø8 | rod, tube or centring bush | slide | hub-clamp-* |
| hub washer thickness | 2 (= rim spacer) | the two leaf hubs either side | designed | hub-clamp-* |

## Sizes

| flexure_od_mm | od_mm | bore_mm | thickness_mm |
|---|---|---|---|
| 40 | 12 | 4 | 2 |
| 60 | 13.2 | 5 | 2 |
| 80 | 17.6 | 5 | 2 |
| 100 | 22 | 8 | 2 |
| 120 | 26.4 | 8 | 2 |

## Where the files are

- NASA (NTRS, public domain): [Free-piston Stirling convertor flexure bearing development and life testing (2005)](https://ntrs.nasa.gov/search?q=20050182933) — PDF — US Government work, public domain
- NASA (NTRS, public domain): [Flexure bearing design for free-piston Stirling engines (1986)](https://ntrs.nasa.gov/search?q=19860020334) — PDF — US Government work, public domain
- NASA (NTRS, public domain): [Advanced Stirling Radioisotope Generator (ASRG) engineering unit (2011)](https://ntrs.nasa.gov/search?q=20110016393) — PDF — US Government work, public domain
- Wikipedia: [Flexure bearing](https://en.wikipedia.org/wiki/Flexure_bearing) — web — CC BY-SA 4.0 (text)
- Sunpower (AMETEK): [Free-piston Stirling technology overview](https://sunpowerinc.com/) — web — Sunpower site (verify at link)
- Long Earth Society: [Engine builds](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/flexure-hub-clamp-washer/index.json

- hub-clamp-40-b4: [STEP](https://xemstudio.com/files/hardware/spiral-flexure-bearings/hub-clamp-40-b4.step) · [STL](https://xemstudio.com/files/hardware/spiral-flexure-bearings/hub-clamp-40-b4.stl) — hub washer Ø12, Ø4 bore, 2 thick (= the rim spacer): between the two leaf hubs of a stack
- hub-clamp-60-b5: [STEP](https://xemstudio.com/files/hardware/spiral-flexure-bearings/hub-clamp-60-b5.step) · [STL](https://xemstudio.com/files/hardware/spiral-flexure-bearings/hub-clamp-60-b5.stl) — hub washer Ø13.2, Ø5 bore, 2 thick (= the rim spacer): between the two leaf hubs of a stack
- hub-clamp-80-b5: [STEP](https://xemstudio.com/files/hardware/spiral-flexure-bearings/hub-clamp-80-b5.step) · [STL](https://xemstudio.com/files/hardware/spiral-flexure-bearings/hub-clamp-80-b5.stl) — hub washer Ø17.6, Ø5 bore, 2 thick (= the rim spacer): between the two leaf hubs of a stack
- hub-clamp-100-b8: [STEP](https://xemstudio.com/files/hardware/spiral-flexure-bearings/hub-clamp-100-b8.step) · [STL](https://xemstudio.com/files/hardware/spiral-flexure-bearings/hub-clamp-100-b8.stl) — hub washer Ø22, Ø8 bore, 2 thick (= the rim spacer): between the two leaf hubs of a stack
- hub-clamp-120-b8: [STEP](https://xemstudio.com/files/hardware/spiral-flexure-bearings/hub-clamp-120-b8.step) · [STL](https://xemstudio.com/files/hardware/spiral-flexure-bearings/hub-clamp-120-b8.stl) — hub washer Ø26.4, Ø8 bore, 2 thick (= the rim spacer): between the two leaf hubs of a stack

## How it fits

### Goes in or on
- [Planar spiral flexure bearing leaves: Ø40 to Ø120, 3-arm and 2-arm, 0.5 and 2 mm](https://xemstudio.com/objects/spiral-flexure-bearing/): between leaf hubs, same bore

### Connects to
- [Flexure hub collars: split collars Ø13.2, Ø17.6 and Ø22 for Ø3 rod and Ø5 tube](https://xemstudio.com/objects/flexure-hub-collar/): collars clamp the hub stack
- [Flexure hub centring bush: Ø5 and Ø8 OD × Ø3 / Ø5 bore × 6](https://xemstudio.com/objects/flexure-hub-centring-bush/): rides on the bush when the rod is smaller than the bore

## Questions

**What size is the hub washer for an Ø80 flexure?**

Ø17.6 × Ø5 bore × 2 mm, the same thickness as the rim spacer.

**Which hub washer goes with which leaf?**

The one with the same OD: Ø12 for Ø40 leaves, Ø13.2 for Ø60, Ø17.6 for Ø80, Ø22 for Ø100, Ø26.4 for Ø120, each with that leaf's bore.

## Fits with

- [Planar spiral flexure bearing leaves: Ø40 to Ø120, 3-arm and 2-arm, 0.5 and 2 mm](https://xemstudio.com/objects/spiral-flexure-bearing/)
- [Flexure hub collars: split collars Ø13.2, Ø17.6 and Ø22 for Ø3 rod and Ø5 tube](https://xemstudio.com/objects/flexure-hub-collar/)
- [Flexure hub centring bush: Ø5 and Ø8 OD × Ø3 / Ø5 bore × 6](https://xemstudio.com/objects/flexure-hub-centring-bush/)
- [Flexure stack spacer ring: Ø40 to Ø120 × 2 mm](https://xemstudio.com/objects/flexure-stack-spacer/)