# Build list: Free-piston Stirling, 2 in tri-clamp (flexure-suspended)

> What parts do I need to build a free-piston Stirling, 2 in tri-clamp?

- Category: Stirling engines › Guide
- Kind: List / guide
- Basis: Every printed part is a free file on this site.
- Page: https://xemstudio.com/objects/list-free-piston-2in/ · JSON: https://xemstudio.com/api/geometry?object=list-free-piston-2in · Plain text: https://xemstudio.com/objects/list-free-piston-2in/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); linked files under their publishers' licenses

**Exact dimensions.** True size, with no printing tolerance added.

## Notes

- No crank: displacer rod through the piston, both hung on spiral flexure stacks; the demonstrator NASA's convertors grew from.
- Numbers: Ø46 × 90 displacer · Ø47.3 piston · Ø80 flexures, 2 stacks · two-row moving-magnet alternator · 10–20 Hz

## Sizes

| subsystem | object | parts | qty | note |
|---|---|---|---|---|
| Hot end | tri-clamp-cups | cup-2in-90 | 1 | printed for a warm-plate demonstrator. |
| Cylinder | tri-clamp-spool | tc-spool-2in-6in | 1 | 16 ga, 47.5 bore |
| Joints | tri-clamp-end-cap | tc-gasket-2in | 2 | ISO 2852 Type B gaskets on the cold joints |
| Clamps | tri-clamp-clamps | clamp-half-2in | 4 | two halves per joint. |
| Displacer | tri-clamp-displacers-and-heads | displacer-shell-2in-90, displacer-cap-2in | 1 | Ø3 rod on the cap's M3 grub |
| Power piston | tri-clamp-power-pistons | piston-2in-f020-rod, lapping-handle-2in | 1 | lap to fit; bushing in the crown |
| Piston plug | tri-clamp-free-piston-kit | fp-piston-plug-2in | 1 | carries the 5 mm tube rod |
| Wrist dowels | dowel-pins-metric | dowel-3x16 | 2 | retain the plug |
| Rod bushing | bearing-housings-and-rod-supports | bushing-3x5x6 | 1 | no oil |
| Rods | brass-tube-ks | brass-5mm | 1 | 5 mm K&S tube piston rod |
| Displacer rod | stirling-shafts-and-rods | rod-3x200 | 1 | through the piston bushing and the tube. |
| Flexure head | tri-clamp-free-piston-kit | fp-flexure-head-2in | 1 | clamps on the spool's open ferrule |
| Flexure ring | tri-clamp-free-piston-kit | fp-flexure-ring-80 | 1 | stack B, on standoffs |
| Stand | spool-hanger-collars | hanger-2in-tab, hanger-2in-plain | 1 | hangs the engine from a 2020 crossbar over the heat |
| Frame rails | t-slot-extrusions | 2020-100 | 3 | two uprights + crossbar; M5 T-nuts |
| Leaves | spiral-flexure-bearings | flexure-80-3arm-w2.5-t2 | 4 | 2 per stack; alternate spiral hand. |
| Stack hardware | spiral-flexure-bearings | spacer-80-t2, clamp-plate-80, hub-clamp-80-b5 | 2 | one set per stack |
| Hub collars | tri-clamp-free-piston-kit | hub-collar-80-b5, hub-collar-80-b3 | 2 | two b5 on the tube, two b3 on the displacer rod |
| Centring bush | tri-clamp-free-piston-kit | hub-bush-80-b3 | 1 | centres stack B's Ø5 hub bores on the Ø3 rod |
| Alternator mover | linear-alternator-kit | alt-mover-35-2x8-10x3 | 1 | on the 5 mm tube above stack A; centre it in the coils, then grub |
| Magnets | neodymium-disc-magnets | magnet-10x3 | 16 | N42 Ø10 × 3: row 1 all N out, row 2 all S out (check with a compass) |
| Alternator stator | linear-alternator-kit | alt-bobbin-37-2x10, alt-housing-2in-flex80, alt-cap-2in-flex80 | 1 | two bays wound opposite ways, in series |
| Back iron | linear-alternator-kit | alt-back-iron-sleeve | 1 | the bobbin slides in; sits on the housing ledge |
| Coils | linear-alternator-kit | alt-coil-bay | 2 | one per bobbin bay, the second wound the opposite way |
| Alternator standoffs | threaded-standoffs-metric | standoff-m3x30 | 3 | between stack A and the housing |
| Alternator screws | socket-head-cap-screws-metric | shcs-m3x16, shcs-m3x10, shcs-m3x12 | 3 | 16 up through head + stack A; 10 housing to standoffs; 12 through top flange + cap |
| Standoffs | threaded-standoffs-metric | standoff-m3x30 | 6 | 3 under the alternator housing, 3 above it to the flexure ring |
| Fasteners | socket-head-cap-screws-metric | shcs-m3x10 | 12 | rims to head and ring |
| Heat | tea-light-candles | tea-light-maxi-58x24 | 1 | or a hot plate under the cup |

## Where the files are

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

## Build order

1. Print the displacer + cap, cup, piston (f020-rod), plug, flexure head, flexure ring, hub collars, centring bush, and the Ø80 printed leaves, spacers, clamp plates and hub washers.
2. Lap the piston in the spool; press the bushing into the crown; plug and dowels in; 5 mm tube into the plug.
3. Displacer on its Ø3 rod; rod through the piston bushing and up the tube.
4. Cup + gasket + spool + gasket + flexure head, clamped.
5. Stack A on the tube: collar · leaf · washer · leaf · collar; rims onto the head with spacer and clamp plate.
6. 3 × M3 × 16 up through the head and stack A into 3 × M3 × 30 standoffs (this clamps stack A).
7. Alternator stator: wind both bobbin bays (the second the other way), join them start-to-start; bobbin into the back-iron sleeve; sleeve into the housing; housing onto the standoffs with 3 × M3 × 10; cap on the top flange with 3 × M3 × 12 into the second set of standoffs.
8. Mover (16 magnets, rows opposite) down over the tube through the cap, centred in the coils at mid-stroke; grub; cut the tube just above it.
9. Flexure ring on the upper standoffs; stack B on the centring bush on the displacer rod, rims to the ring.
10. Centre both stacks at mid-stroke before tightening the collars; heat the cup; tap the tube to start.

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

## Questions

**What parts do I need to build a Free-piston Stirling, 2 in tri-clamp?**

39 parts, every one a free STEP/STL on this site; see the table and the build order on this page.

**How do I download every STL for this build at once?**

The stl-list.txt on this page lists every printed part's STL URL.

## Fits with

- [Tri-clamp cups: closed-end spools (ferrule on a capped tube), 1.5, 2 and 3 in](https://xemstudio.com/objects/tri-clamp-cups/)
- [Tri-clamp spool (two ferrules on a tube), 1.5 and 2 inch](https://xemstudio.com/objects/tri-clamp-spool/)
- [Tri-clamp end cap and gasket, 1.5 and 2 inch](https://xemstudio.com/objects/tri-clamp-end-cap/)
- [Tri-clamp clamps (printable two-bolt), hot-joint gaskets and heat shields: every flange size, ½ to 4 in](https://xemstudio.com/objects/tri-clamp-clamps/)
- [Tri-clamp displacers and engine heads: 1.5, 2 and 3 in spools](https://xemstudio.com/objects/tri-clamp-displacers-and-heads/)
- [Tri-clamp power pistons and crank linkage: full-bore ring-less pistons, con-rods, crank webs and a clamp-on crank frame for 1.5, 2 and 3 in spools](https://xemstudio.com/objects/tri-clamp-power-pistons/)
- [Tri-clamp free-piston kit: flexure head, stack ring, hub collars and piston plug for 1.5, 2 and 3 in spools](https://xemstudio.com/objects/tri-clamp-free-piston-kit/)
- [Dowel pins, 2–6 mm (ISO 2338 / DIN 6325)](https://xemstudio.com/objects/dowel-pins-metric/)
- [Bearing housings and linear supports: KP08, KFL08, SK8, SC8UU, V-wheels, sleeve bushings](https://xemstudio.com/objects/bearing-housings-and-rod-supports/)
- [Hobby brass tube (K&S), 1/16–21/32 in and 1–12 mm, telescoping](https://xemstudio.com/objects/brass-tube-ks/)
- [Stirling shafts and rods: Ø3 rods, Ø5 / Ø8 D-flat crankshafts, Ø5 tube rods, Ø3 pins, thrust spacers](https://xemstudio.com/objects/stirling-shafts-and-rods/)
- [Spool hanger collars: clamp a tri-clamp spool to 2020 extrusion over the flame (1.5, 2, 3 in)](https://xemstudio.com/objects/spool-hanger-collars/)