# Flexure ring for the displacer stack: Ø76, Ø96 and Ø116 with Ø60, Ø80 and Ø100 seats

> What holds the displacer's flexure stack above a free-piston head?

- Category: Stirling engines › Free-piston
- Kind: Hardware
- Basis: Ring Ø = flexure OD + 16, 4 mm thick, flexure-OD × 1 seat, 3 × Ø3.4 on the 0.88 × OD circle (same as the flexure head)
- Page: https://xemstudio.com/objects/tri-clamp-flexure-ring/ · JSON: https://xemstudio.com/api/geometry?object=tri-clamp-flexure-ring · Plain text: https://xemstudio.com/objects/tri-clamp-flexure-ring/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

- The ring that carries the displacer's flexure stack (stack B) on three M3 standoffs above the flexure head.
- Ø76 / Ø96 / Ø116 × 4 mm for Ø60 / Ø80 / Ø100 leaves, with a seat the flexure OD × 1 mm deep, a centre window hub + 6 (Ø19.2 / Ø23.6 / Ø28), and three Ø3.4 holes on the same circle as the head (Ø52.8 / Ø70.4 / Ø88).

## 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 |
|---|---|---|---|---|
| flexure pocket in the head / ring | flexure OD | spiral flexure leaf rim | slide | fp-flexure-* |
| rim holes (head, ring) | Ø3.4 | M3 screw clearance | designed | fp-flexure-* |
| head / ring window | hub + 12 (Ø29.6 on Ø80) | hub collars and their pinch-screw heads (no contact) | designed | fp-flexure-* |

## Sizes

| flexure_od_mm | ring_od_mm | thickness_mm | seat_mm | window_mm | hole_circle_mm |
|---|---|---|---|---|---|
| 60 | 76 | 4 | Ø60 × 1 | 19.2 | 52.8 |
| 80 | 96 | 4 | Ø80 × 1 | 23.6 | 70.4 |
| 100 | 116 | 4 | Ø100 × 1 | 28.0 | 88.0 |

## Where the files are

- NASA NTRS: [Free-piston Stirling convertor flexure bearing development and life testing](https://ntrs.nasa.gov/citations/20050182933) — pdf — US Government work
- Long Earth Society: [Tri-clamp Stirling engine builds](https://longearthsociety.com/engineering/) — web, video — LES site
- Wikipedia: [Free-piston engine](https://en.wikipedia.org/wiki/Free-piston_engine) — web — CC BY-SA 4.0 (text)

## Free STEP/STL (3 parts, CC BY 4.0, Xem Studio)

Index: https://xemstudio.com/files/hardware/tri-clamp-flexure-ring/index.json

- fp-flexure-ring-60: [STEP](https://xemstudio.com/files/hardware/tri-clamp-free-piston-kit/fp-flexure-ring-60.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-free-piston-kit/fp-flexure-ring-60.stl) — Ø76 × 4 ring for stack B (displacer rod) on 3 × M3 standoffs above the head: Ø60 × 1 flexure pocket, Ø25.2 window, 3 × Ø3.4
- fp-flexure-ring-80: [STEP](https://xemstudio.com/files/hardware/tri-clamp-free-piston-kit/fp-flexure-ring-80.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-free-piston-kit/fp-flexure-ring-80.stl) — Ø96 × 4 ring for stack B (displacer rod) on 3 × M3 standoffs above the head: Ø80 × 1 flexure pocket, Ø29.6 window, 3 × Ø3.4
- fp-flexure-ring-100: [STEP](https://xemstudio.com/files/hardware/tri-clamp-free-piston-kit/fp-flexure-ring-100.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-free-piston-kit/fp-flexure-ring-100.stl) — Ø116 × 4 ring for stack B (displacer rod) on 3 × M3 standoffs above the head: Ø100 × 1 flexure pocket, Ø34 window, 3 × Ø3.4

## How it fits

### Connects to
- [Tri-clamp flexure head: ISO 2852 cap with Ø60, Ø80 and Ø100 flexure seats](https://xemstudio.com/objects/tri-clamp-flexure-head/): 3 × M3 standoffs on the shared hole circle
- [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/): leaf rim in the seat

### Also needed
- [Threaded standoffs, M2.5 and M3 (hex and round)](https://xemstudio.com/objects/threaded-standoffs-metric/): M3 standoffs

## Questions

**How far is the flexure ring above the head?**

Set by the M3 standoffs between them; the stack-B height sets the displacer's moving mass and phase.

**Which ring goes with the 2 inch head?**

Fp-flexure-ring-80: Ø96 × 4 with the Ø80 seat.

## Fits with

- [Tri-clamp flexure head: ISO 2852 cap with Ø60, Ø80 and Ø100 flexure seats](https://xemstudio.com/objects/tri-clamp-flexure-head/)
- [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/)
- [Threaded standoffs, M2.5 and M3 (hex and round)](https://xemstudio.com/objects/threaded-standoffs-metric/)
- [Flexure hub collars: split collars Ø13.2, Ø17.6 and Ø22 for Ø3 rod and Ø5 tube](https://xemstudio.com/objects/flexure-hub-collar/)