# Build list: Free-piston Stirling generator, 2 in tri-clamp (pressurised, linear alternator)

> What parts do I need to build a Free-piston Stirling generator, 2 in tri-clamp (pressurised, linear alternator)?

- Category: Stirling engines › Assembled engines
- Kind: List / guide
- Basis: Every part is a free STEP/STL on this site or a standard part with its own page; quantities are the full count, every screw, nut, pin, gasket and clamp.
- Page: https://xemstudio.com/objects/list-fpse-generator-2in/ · JSON: https://xemstudio.com/api/geometry?object=list-fpse-generator-2in · Plain text: https://xemstudio.com/objects/list-fpse-generator-2in/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.** True size, with no printing tolerance added.

## Notes

- A real free-piston Stirling generator in standard 2 in sanitary fittings: closed-end hot spool over a torch, annular screen regenerator, flexure leaves clamped in the joints, a magnet-carrying power piston in a bored spool with the alternator outside its wall, helium or air at up to 10 bar.
- Numbers: Ø48 piston ±5 mm, Ø39.4 displacer ±4.5 leading 68° · 45 Hz · helium 10 bar: 43 W electrical, 24 % of 180 W into the head · air 10 bar 28 W · 1 bar: 0.1 W helium, 0.1 W air · relief 15 bar g

## Sizes

| subsystem | object | parts | qty | note |
|---|---|---|---|---|
| None | tri-clamp-torch-stand | torch-stand-40 | 1 | on the bench under the hot end, post toward +Y; the heat source is a propane or butane torch head in its ring |
| None | set-screws-metric | set-m4x10 | 3 | centre the torch head in the ring |
| None | tri-clamp-split-burner-shroud | shroud-half-2in-split | 2 | round the hot end, lids clamped on the tube above the fins |
| None | tri-clamp-hot-end-fin-sleeve | fin-sleeve-half-2in-76 | 2 | optional heat exchanger: clamped on the lower 66 mm of S1 |
| None | socket-head-cap-screws-metric | shcs-m4x16 | 4 | optional, with the fin sleeve: its ears |
| None | tri-clamp-closed-end-spool | closed-spool-2in-152.4 | 1 | S1, the hot end: closed end down |
| None | fpse-displacer-cylinder | fpse-liner-40-rim64 | 1 | in S1, rim clamped in joint A |
| None | fpse-fin-inserts | fpse-heater-insert-41.5x47.5 | 1 | optional heat exchanger: on the liner's lower end |
| None | fpse-regenerator-screen-ring | regen-ring-41.5x47.5x0.2 | 389 | 100 mesh screen rings, stacked on the liner's spokes up to its rim |
| None | tri-clamp-leaf-half-gasket | leaf-half-gasket-2in-w0.45 | 6 | two each at joint A (liner rim), C and D (piston leaves), beads outward |
| None | tri-clamp-leaf-half-gasket | leaf-half-gasket-2in-w0.6 | 2 | joint B, round the displacer leaf |
| None | sanitary-high-pressure-clamp | hp-clamp-2in | 5 | rated above the 15 bar gauge relief setting |
| None | tri-clamp-spool | tc-spool-2in-3in | 2 | S3 (cooler and compression space) and S5 (bounce space between the piston leaves) |
| None | fpse-fin-inserts | fpse-cooler-insert-40x47.5 | 1 | optional heat exchanger: pressed into S3 |
| None | tri-clamp-clamp-on-water-jacket | water-jacket-half-2in-20 | 2 | optional heat exchanger: on S3 above its hanger, hoses in series |
| None | socket-head-cap-screws-metric | shcs-m4x12 | 2 | optional, with the jacket: its ears |
| None | fpse-displacer | fpse-displacer-shell-39.4 | 1 | hot end down, in the liner |
| None | fpse-displacer | fpse-displacer-cap-39.4 | 1 | closes the shell; its boss carries leaf B's hub |
| None | tri-clamp-flexure-leaf | leaf-2in-displacer-t0.5 | 1 | joint B: the displacer's leaf |
| None | fpse-hub-collars | fpse-collar-12x20 | 1 | on the rod over leaf B's hub |
| None | fpse-displacer-rod | fpse-displacer-rod-12x10 | 1 | in the cap's socket, up through the piston |
| None | fpse-displacer-rod | fpse-rod-plug-12 | 1 | in the rod's top |
| None | fpse-displacer-rod | fpse-stinger-3x87.05 | 1 | plug to the gas-spring piston, through the gland |
| None | fpse-displacer-gas-spring | fpse-gas-spring-piston-18 | 1 | on the stinger, in the gas-spring cylinder |
| None | fpse-displacer-gas-spring | fpse-gas-spring-gland-18 | 1 | closes the gas-spring cylinder's bottom |
| None | fpse-displacer-gas-spring | fpse-gas-spring-cylinder-18 | 1 | pressed into the top of S6 |
| None | socket-head-cap-screws-metric | shcs-m3x16 | 3 | gland to the gas-spring cylinder, heads underneath |
| None | set-screws-metric | set-m3x4 | 7 | collars (5), rod plug (1), gas-spring piston (1) |
| None | tri-clamp-bored-spool | spool-2in-6in-bored-48.00 | 1 | S4: the power cylinder, Ø48.00 bore |
| None | fpse-power-piston | fpse-piston-48-40mag | 1 | in S4, crown down |
| None | neodymium-disc-magnets | magnet-12x3 | 40 | 4 rows of 10, faces out: S, N, N, S from the crown up |
| None | fpse-power-piston | fpse-piston-top-plate | 1 | in the carrier's bore on the hub |
| None | fpse-power-piston | fpse-tube-rod-18x14 | 1 | piston to above leaf D |
| None | tri-clamp-flexure-leaf | leaf-2in-piston-t0.8 | 2 | joints C and D; D turned over (opposite hand) |
| None | fpse-hub-collars | fpse-collar-18x28 | 4 | two each side of each piston leaf's hub |
| None | fpse-linear-alternator-stator | fpse-stator-pack-43deg | 8 | round S4 at the magnets' height |
| None | fpse-linear-alternator-stator | fpse-bobbin-65 | 1 | between the teeth; slid over S4's flange first |
| None | fpse-linear-alternator-stator | fpse-coil-300t | 1 | 300 turns of 0.71 mm enamelled wire on the bobbin |
| None | fpse-linear-alternator-stator | fpse-stator-housing-half | 2 | clamp the packs onto S4 |
| None | socket-head-cap-screws-metric | shcs-m4x20 | 10 | stator housing (4), shroud lids (2), hanger ears (4) |
| None | hex-nuts-metric | nut-m4 | 16 | stator housing (4), shroud (2), hanger ears (4), fin sleeve (4, optional), jacket (2, optional) |
| None | tri-clamp-spool | tc-spool-2in-6in | 1 | S6: holds the displacer's gas spring |
| None | tri-clamp-gasket | tc-gasket-2in | 1 | joint E under the port cap |
| None | tri-clamp-port-cap | port-cap-2in-4x-npt18 | 1 | on S6: fill valve, pressure gauge, relief valve, and a plug or pressure transducer |
| None | npt-thread-envelopes | npt-1-8-male | 4 | the 1/8 NPT stems of the fill valve, gauge, relief valve and plug (bodies are the builder's choice) |
| None | 2020-aluminum-extrusion | 2020-300 | 2 | uprights; they end below the stator |
| None | 2020-aluminum-extrusion | 2020-200 | 2 | rails on the bench behind the uprights, clamped or screwed to the bench |
| None | t-slot-corner-brackets | corner-bracket-20 | 4 | two per upright |
| None | button-head-screws-metric | button-m5x10 | 8 | bracket screws |
| None | flat-washers-metric | washer-m5 | 8 |  |
| None | drop-in-t-nuts | tnut-dropin-20-m5 | 12 | 8 brackets, 2 per hanger |
| None | spool-hanger-collars | hanger-2in-tab | 2 | two stacked on S3, below the jacket |
| None | spool-hanger-collars | hanger-2in-plain | 2 |  |
| None | socket-head-cap-screws-metric | shcs-m5x16 | 4 | hanger bars into the uprights' T-nuts |

## Where the files are

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

## Build order

1. Torch stand on the bench (post toward +Y), torch head in its ring. Rails, uprights, brackets; the rails clamped or screwed to the bench (the engine vibrates).
2. Hot spool S1 closed end down. Heater insert onto the liner's lower end; liner into S1; the 389 screen rings into the annulus up to the rim's underside.
3. Half gasket (bead down) on S1's face, the liner's rim on it, half gasket (bead up); S3 on top (cooler insert pressed in first); high-pressure clamp A.
4. Displacer: cap pressed into the shell; rod into the cap's socket; displacer down into the liner. Leaf B between half gaskets on S3's face over the cap's boss; collar on the rod onto the hub, grub.
5. Piston: 40 magnets into their pockets (S, N, N, S rows from the crown); top plate; tube rod. Coil (on its bobbin) over S4's flange and down to the magnets' height; S4 on joint B, clamp B; piston down S4 over the rod.
6. Stator packs round S4 at the coil, housing halves with 4 × M4 × 20; leads out through the housing's hole. Collar, half gasket, leaf C, half gasket, S5, collar; clamp C. Collar, leaf D (turned over) between half gaskets, collar; S6; clamp D.
7. Rod plug into the rod's top with the stinger; gas-spring piston on the stinger; gland and cylinder over it (3 × M3 × 16); cylinder pressed into S6's top. Type B gasket, port cap, clamp E; fill valve, gauge, relief valve, plug.
8. Two hangers stacked on S3 below the jacket (never clamp anything over S4's bored seal zone); shroud and fin sleeve on S1; jacket on S3; turn every clamp's bolt to the front (+Y). Charge slowly, connect the load and its series capacitor, then light the burner.

All printed STLs: https://xemstudio.com/objects/list-fpse-generator-2in/stl-list.txt

## Questions

**Does a free-piston Stirling work at this small size?**

Yes when pressurised: power goes with mean pressure, swept volume and frequency. My analysis gives 43 W at 10 bar helium and 0.1 W at 1 bar air from this 48 mm piston at ±5 mm. NASA's Sunpower ASC makes about 80 W from a 1.3 kg convertor on helium; Sunpower's EG-1000 1.1 kW at 50 Hz on 3.0 MPa helium.

**What charge pressure, and what ratings?**

10 bar running for tens of watts; relief at 15 bar gauge; the clamps (high-pressure bolted, published 1000 psi at 70–75 °F, 800 psi at 250 °F) and the gaskets must be rated above the relief setting at their temperature.

**Where is the electricity?**

Two leads from the coil outside the vessel: 41 V peak open circuit at the design point, 43 W into 12 Ω with a 500 µF series capacitor. Rectify and regulate it; never leave the coil open while the engine runs (the load sets the stroke).

**What are the risks?**

Over-stroke if the load drops (keep a dump resistor switched in), the displacer's tuning (its mass and the gas-spring column set its phase), alignment of the rod through the piston across the joints, the leaves' fatigue, vibration (about 436 N peak), and the clamps and gaskets at temperature.

## Fits with

- [Free-piston Stirling generator, 2 in tri-clamp: performance, dynamics and losses (air and helium, 1 and 10 bar)](https://xemstudio.com/objects/fpse-generator-2in-performance/)
- [Tri-clamp closed-end spool: 2 in × 152.4 mm (6 in) with a welded closed end, the hot end of a pressurised Stirling](https://xemstudio.com/objects/tri-clamp-closed-end-spool/)
- [Tri-clamp spool bored and honed: 2 in × 6 in, bore Ø48.00, a power-piston cylinder](https://xemstudio.com/objects/tri-clamp-bored-spool/)
- [Free-piston power piston: Ø48 clearance-seal land, 40-magnet carrier, top plate and tube rod](https://xemstudio.com/objects/fpse-power-piston/)
- [Moving-magnet linear alternator stator outside a 2 in tri-clamp spool: laminated two-tooth stator, one coil](https://xemstudio.com/objects/fpse-linear-alternator-stator/)
- [Tri-clamp flexure leaf: spiral planar spring clamped in a 2 in joint like a gasket (displacer and piston)](https://xemstudio.com/objects/tri-clamp-flexure-leaf/)
- [Free-piston displacer gas spring: double-acting Ø18 cylinder, gland and piston in a 2 in tri-clamp spool](https://xemstudio.com/objects/fpse-displacer-gas-spring/)
- [High-pressure bolted sanitary clamp, 2 in (bought part: ratings, no drawing)](https://xemstudio.com/objects/sanitary-high-pressure-clamp/)
- [Build list: Free-piston Stirling, 2 in tri-clamp (flexure-suspended)](https://xemstudio.com/objects/list-free-piston-2in/)