# Flexure rim clamp plate: Ø40 to Ø120 × 3 mm, 3 × M3

> What clamps the rims of a flexure bearing stack?

- Category: Stirling engines › Free-piston
- Kind: Hardware
- Basis: Ring = the flexure rim (OD, width 0.12 OD), 3 mm thick, 3 × Ø3.4 on the 0.88 × OD circle
- Page: https://xemstudio.com/objects/flexure-rim-clamp-plate/ · JSON: https://xemstudio.com/api/geometry?object=flexure-rim-clamp-plate · Plain text: https://xemstudio.com/objects/flexure-rim-clamp-plate/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 3 mm ring the size of the leaf rim with three Ø3.4 holes on the rim-hole circle: it clamps the stack of leaf rims and spacers down to the head.
- Ø40 to Ø120; hole circles Ø35.2 / 52.8 / 70.4 / 88 / 105.6, matching the leaves and the tri-clamp flexure head.

## 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 |
|---|---|---|---|---|
| clamp-plate holes | Ø3.4 | M3 screw clearance | designed | clamp-plate-* |

## Sizes

| od_mm | width_mm | thickness_mm | holes | hole_circle_mm |
|---|---|---|---|---|
| 40 | 4.8 | 3 | 3 × Ø3.4 | 35.2 |
| 60 | 7.2 | 3 | 3 × Ø3.4 | 52.8 |
| 80 | 9.6 | 3 | 3 × Ø3.4 | 70.4 |
| 100 | 12 | 3 | 3 × Ø3.4 | 88.0 |
| 120 | 14.4 | 3 | 3 × Ø3.4 | 105.6 |

## 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-rim-clamp-plate/index.json

- clamp-plate-40: [STEP](https://xemstudio.com/files/hardware/spiral-flexure-bearings/clamp-plate-40.step) · [STL](https://xemstudio.com/files/hardware/spiral-flexure-bearings/clamp-plate-40.stl) — rim clamp plate Ø40, 3 thick, 3 × Ø3.4 (M3) on R17.6
- clamp-plate-60: [STEP](https://xemstudio.com/files/hardware/spiral-flexure-bearings/clamp-plate-60.step) · [STL](https://xemstudio.com/files/hardware/spiral-flexure-bearings/clamp-plate-60.stl) — rim clamp plate Ø60, 3 thick, 3 × Ø3.4 (M3) on R26.4
- clamp-plate-80: [STEP](https://xemstudio.com/files/hardware/spiral-flexure-bearings/clamp-plate-80.step) · [STL](https://xemstudio.com/files/hardware/spiral-flexure-bearings/clamp-plate-80.stl) — rim clamp plate Ø80, 3 thick, 3 × Ø3.4 (M3) on R35.2
- clamp-plate-100: [STEP](https://xemstudio.com/files/hardware/spiral-flexure-bearings/clamp-plate-100.step) · [STL](https://xemstudio.com/files/hardware/spiral-flexure-bearings/clamp-plate-100.stl) — rim clamp plate Ø100, 3 thick, 3 × Ø3.4 (M3) on R44
- clamp-plate-120: [STEP](https://xemstudio.com/files/hardware/spiral-flexure-bearings/clamp-plate-120.step) · [STL](https://xemstudio.com/files/hardware/spiral-flexure-bearings/clamp-plate-120.stl) — rim clamp plate Ø120, 3 thick, 3 × Ø3.4 (M3) on R52.8

## 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/): on top of the leaf rims

### Connects to
- [Tri-clamp flexure head: ISO 2852 cap with Ø60, Ø80 and Ø100 flexure seats](https://xemstudio.com/objects/tri-clamp-flexure-head/): same three-hole circle

### Also needed
- [Socket head cap screws, M2–M8 (ISO 4762 / DIN 912)](https://xemstudio.com/objects/socket-head-cap-screws-metric/): 3 × M3

## Questions

**What screws hold the flexure clamp plate?**

Three M3 through Ø3.4 holes on the rim circle (Ø70.4 for the Ø80 plate).

**How thick is the clamp plate?**

3 mm.

## 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 stack spacer ring: Ø40 to Ø120 × 2 mm](https://xemstudio.com/objects/flexure-stack-spacer/)
- [Tri-clamp flexure head: ISO 2852 cap with Ø60, Ø80 and Ø100 flexure seats](https://xemstudio.com/objects/tri-clamp-flexure-head/)
- [Socket head cap screws, M2–M8 (ISO 4762 / DIN 912)](https://xemstudio.com/objects/socket-head-cap-screws-metric/)