# Alpha V-twin frame for two 10 mL syringes: frame, crank disc and con-rods sized so it actually runs

> How do I hold two syringes and a crank together for an alpha Stirling engine?

- Category: Stirling engines › Drives & mechanisms
- Kind: Hardware
- Basis: Computed in the generator: crank throw 8, rod 60, 10 mL syringe piston (pin 8.6 above the skirt, 19 long), barrel 15.9 OD / 14.5 ID; checked over a full turn: skirt never closer than the barrel mouth, rod never within 0.5 mm of the barrel wall
- Page: https://xemstudio.com/objects/alpha-v-twin-frame/ · JSON: https://xemstudio.com/api/geometry?object=alpha-v-twin-frame · Plain text: https://xemstudio.com/objects/alpha-v-twin-frame/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

- Phase: in a 90° V both con-rods ride ONE crank pin, and the 90° between the cylinders is the 90° alpha phase. (A two-pin disc with pins 90° apart is for parallel cylinders; under a 90° V it would give 0° or 180° and the engine would not run.)
- Geometry: crank axis at the origin; both barrel axes pass through it at ±45°. Barrel sockets start at R45 so the piston (bottom of skirt 43.4 mm from the axis at bottom dead centre) never leaves the barrel, and with a 60 mm rod the rod swings at most ±7.7°, keeping 0.8 mm from the barrel wall.
- Along the shaft (Y): 625 · boss · 625, 2 mm spacer, crank disc (6), 1 mm spacer, rod 1 (cylinder at +45°), 1 mm spacer, rod 2 (cylinder at −45°), Ø3 × 20 pin pressed 6 mm into the disc, 3 mm collar on its end. Flywheel (nut-weighted Ø100, b5) on the other end of the Ø5 × 80 shaft behind the boss.
- Barrels slide in from the crank side, tip outward, finger flange against the socket's inner face; M3 pinch screw. Pistons: syringe-piston-10ml (no plunger). Transfer: a short tube with a mesh plug between the tips (transfer tee).
- Foot: 2 × M5 at 50 mm into a 2020 rail; mount it at the rail's end so the flywheel hangs clear. Print the frame on its back (the plate on the bed).
- LES: the two-syringe alpha, complete.

## 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 |
|---|---|---|---|---|
| barrel sockets | Ø15.9 | 10 mL syringe barrel | socket | alpha-frame-* |
| bearing pockets | Ø16 | 625 bearing | press | alpha-frame-* |
| crank-disc bore | Ø5 | Ø5 crankshaft (M3 grub) | slide | alpha-crank-disc-* |
| crank-disc pin hole | Ø3 | Ø3 × 20 crank pin | press | alpha-crank-disc-* |
| con-rod ends | Ø3 | Ø3 pins (turn on them) | run | alpha-conrod-* |

## Sizes

| parameter | value | note |
|---|---|---|
| crank throw | 8.0 | stroke 16 → 2.6 mL per cylinder |
| con-rod | 60.0 | Ø3 plain ends, H8/f7 |
| V angle | 90 | = phase |
| socket inner face | 45.0 | radius from crank axis |
| min skirt radius | 43.4 | ≥ barrel mouth |
| rod-to-wall margin | 0.83 | > 0 |
| shaft | Ø5 × 80 | 2 × 625 |
| rod planes (Y) | 9.5 / 15.5 | 1 mm spacers |

## Where the files are

- Long Earth Society: [Engine builds](https://longearthsociety.com/engineering/) — web, video — LES site
- Wikipedia: [Stirling engine (alpha configuration)](https://en.wikipedia.org/wiki/Stirling_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/alpha-v-twin-frame/index.json

- alpha-frame-10ml: [STEP](https://xemstudio.com/files/hardware/alpha-v-twin-frame/alpha-frame-10ml.step) · [STL](https://xemstudio.com/files/hardware/alpha-v-twin-frame/alpha-frame-10ml.stl) — alpha V-twin frame: Ø5 shaft in two 625s (pockets both ends of the Ø24 boss), two 10 mL barrel sockets at ±45° whose axes meet the crank axis, inner faces at R45, M3 pinch screws, foot with 2 × M5 at 50 mm for 2020
- alpha-crank-disc-s16: [STEP](https://xemstudio.com/files/hardware/alpha-v-twin-frame/alpha-crank-disc-s16.step) · [STL](https://xemstudio.com/files/hardware/alpha-v-twin-frame/alpha-crank-disc-s16.stl) — crank disc Ø26 × 6, Ø5 bore (H7/h6), tapped M3 grub, ONE Ø3 pin at 8 mm (stroke 16): both con-rods share it
- alpha-conrod-60: [STEP](https://xemstudio.com/files/hardware/alpha-v-twin-frame/alpha-conrod-60.step) · [STL](https://xemstudio.com/files/hardware/alpha-v-twin-frame/alpha-conrod-60.stl) — con-rod 60 mm, 8 wide × 5, Ø3 plain ends (H8/f7 running on the pins; print or make two): small end in the syringe piston's 5.4 mm fork

## How it fits

### Connects to
- [Syringe pistons: ring-less printed pistons with a con-rod fork for 10, 20 and 30 mL syringe barrels](https://xemstudio.com/objects/syringe-pistons/): two 10 mL pistons on the 60 mm rods
- [Plastic syringes 1–60 mL as pistons and cylinders](https://xemstudio.com/objects/plastic-syringes/): 10 mL barrels in the sockets
- [Nut-weighted flywheels: Ø100–200 with hex pockets for M8, M10, M12, 3/8 and 1/2 in nuts](https://xemstudio.com/objects/nut-weighted-flywheels/): Ø100 b5 behind the boss

### Alternatives
- [Ross yoke alpha for two parallel 10 mL syringes: frame, yoke, rocking link, crank and con-rods, solved for 90°](https://xemstudio.com/objects/ross-yoke-kit/): parallel-cylinder alpha, solved for 90°

### Also needed
- [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/): Ø5 × 80 crankshaft, Ø3 × 20 pin, spacers
- [Ball bearings, 683 to 6210 and flanged F6xx (ISO 15)](https://xemstudio.com/objects/ball-bearings-metric/): 2 × 625
- [Alpha V-twin: 90° two-pin crank discs, V block, transfer tee](https://xemstudio.com/objects/alpha-twin-crank-90/): transfer tee
- [Aluminium T-slot extrusion: 2020, 2040, 2060, 2080, V-slot, 3030, 3060, 4040, 4080, 1010, 1515](https://xemstudio.com/objects/t-slot-extrusions/): 2020 rail under the foot

## Questions

**How do I get 90° phase on a two-syringe alpha Stirling?**

Put the syringes in a 90° V and run both con-rods on one crank pin; the V angle is the phase. The alpha frame does exactly that.

**Why a 60 mm con-rod?**

A shorter rod swings further and hits the inside of a 14.5 mm syringe barrel near the mouth; at 60 mm and 16 mm stroke it clears the wall by about 0.8 mm while the piston stays fully inside the barrel.

## Fits with

- [Syringe pistons: ring-less printed pistons with a con-rod fork for 10, 20 and 30 mL syringe barrels](https://xemstudio.com/objects/syringe-pistons/)
- [Plastic syringes 1–60 mL as pistons and cylinders](https://xemstudio.com/objects/plastic-syringes/)
- [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/)
- [Nut-weighted flywheels: Ø100–200 with hex pockets for M8, M10, M12, 3/8 and 1/2 in nuts](https://xemstudio.com/objects/nut-weighted-flywheels/)
- [Alpha V-twin: 90° two-pin crank discs, V block, transfer tee](https://xemstudio.com/objects/alpha-twin-crank-90/)
- [Ball bearings, 683 to 6210 and flanged F6xx (ISO 15)](https://xemstudio.com/objects/ball-bearings-metric/)
- [Aluminium T-slot extrusion: 2020, 2040, 2060, 2080, V-slot, 3030, 3060, 4040, 4080, 1010, 1515](https://xemstudio.com/objects/t-slot-extrusions/)