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Syringe pistons: ring-less printed pistons with a con-rod fork for 10, 20 and 30 mL syringe barrels
How do I connect a syringe to a crank for a Stirling engine without the rubber plunger's friction? · Hardware · basis: Barrel IDs from the plastic-syringes entry (10 mL 14.5, 20 mL 19.1, 30 mL 21.7 mm); same two-land, print-and-lap method as the tri-clamp power pistons
Long Earth Society build part. Pistons for the syringe engines. The engines
- sizes
- 9 in table
Notes
- The rubber tip of a syringe plunger seals by squeezing the wall: far too much friction for a Stirling. Throw the plunger away and run a printed piston in the barrel instead, lapped to fit like the tri-clamp pistons (sinks slowly under its own weight, holds with the tip capped).
- Each piston has a 5.4 mm fork slot open to the bottom and a Ø3 pin hole across it at 0.45 L: the Ross yoke kit's conrod-45 (5 mm thick, Ø3.2 ends) or the crank kit's con-rods drop straight in on a 3 × 12 dowel. The fork keeps the con-rod inside the barrel's footprint, so the piston can enter the barrel past the pin.
- Fits: f008 / f015 are 0.08 / 0.15 mm under the barrel; lap is 0.08 over, to lap down. Plastic barrels vary by brand, so measure yours with calipers and pick the closest; lap with 1500 grit and graphite, run dry.
- Used by: the Ross yoke alpha (cylinder block for two 10 mL barrels), the alpha 90° V-block, the gamma power head (10 mL socket) and the can engine.
- LES: the syringe engines' pistons.
Sizes
| syringe | barrel_id_mm | piston_od_mm | length_mm | offset_mm | pin_z_mm |
|---|---|---|---|---|---|
| 10ml | 14.5 | 14.58 | 19 | +0.08 | 8.6 |
| 10ml | 14.5 | 14.42 | 19 | -0.08 | 8.6 |
| 10ml | 14.5 | 14.35 | 19 | -0.15 | 8.6 |
| 20ml | 19.1 | 19.18 | 25 | +0.08 | 11.2 |
| 20ml | 19.1 | 19.02 | 25 | -0.08 | 11.2 |
| 20ml | 19.1 | 18.95 | 25 | -0.15 | 11.2 |
| 30ml | 21.7 | 21.78 | 28 | +0.08 | 12.6 |
| 30ml | 21.7 | 21.62 | 28 | -0.08 | 12.6 |
| 30ml | 21.7 | 21.55 | 28 | -0.15 | 12.6 |
Where the files are
Other publishers' files are linked, not hosted. "verify" = check the license at the link before commercial use.
| Long Earth Society | Engine builds | web, video | LES site |
Free files
★ Free files 9 parts. Generated by Xem Studio from the standard; threads are plain cylinders at major diameter. CC BY 4.0. index.json
| syringe-piston-10ml-lap | 10ml syringe piston Ø14.58 × 19 (lapping stock, +0.08), two 5 mm lands, 5.4 mm fork slot, Ø3 pin at 8.6 mm | STEP · STL |
| syringe-piston-10ml-f008 | 10ml syringe piston Ø14.42 × 19 (0.08 under the 14.5 barrel), two 5 mm lands, 5.4 mm fork slot, Ø3 pin at 8.6 mm | STEP · STL |
| syringe-piston-10ml-f015 | 10ml syringe piston Ø14.35 × 19 (0.15 under the 14.5 barrel), two 5 mm lands, 5.4 mm fork slot, Ø3 pin at 8.6 mm | STEP · STL |
| syringe-piston-20ml-lap | 20ml syringe piston Ø19.18 × 25 (lapping stock, +0.08), two 5 mm lands, 5.4 mm fork slot, Ø3 pin at 11.2 mm | STEP · STL |
| syringe-piston-20ml-f008 | 20ml syringe piston Ø19.02 × 25 (0.08 under the 19.1 barrel), two 5 mm lands, 5.4 mm fork slot, Ø3 pin at 11.2 mm | STEP · STL |
| syringe-piston-20ml-f015 | 20ml syringe piston Ø18.95 × 25 (0.15 under the 19.1 barrel), two 5 mm lands, 5.4 mm fork slot, Ø3 pin at 11.2 mm | STEP · STL |
| syringe-piston-30ml-lap | 30ml syringe piston Ø21.78 × 28 (lapping stock, +0.08), two 5 mm lands, 5.4 mm fork slot, Ø3 pin at 12.6 mm | STEP · STL |
| syringe-piston-30ml-f008 | 30ml syringe piston Ø21.62 × 28 (0.08 under the 21.7 barrel), two 5 mm lands, 5.4 mm fork slot, Ø3 pin at 12.6 mm | STEP · STL |
| syringe-piston-30ml-f015 | 30ml syringe piston Ø21.55 × 28 (0.15 under the 21.7 barrel), two 5 mm lands, 5.4 mm fork slot, Ø3 pin at 12.6 mm | STEP · STL |
Plain text: sheet.txt · JSON: /api/geometry?object=syringe-pistons
How it fits
Goes in or on
Plastic syringes 1–60 mL as pistons and cylindersruns in the barrel; plunger discardedConnects to
Alpha V-twin frame for two 10 mL syringestwo pistons in the alpha frame
Ross yoke kitconrod-45 in the fork
Alpha V-twinV-block alpha
Crank discs, connecting rods and flywheels for…con-rods
Can-engine printed kitcan engine power pistonAlternatives
Tri-clamp power pistons and crank linkagefull-bore tri-clamp pistons
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Dowel pins, 2–6 mmØ3 × 12 piston pin
Printer calibration couponsset the slicer firstIn these build lists
Soda-can gammaCan, tea light, foam, syringe, skewer, CD: the first engine, no budget.LTD coffee-cup engineRuns on a cup of coffee: wide thin displacer, tiny piston.Alpha V-twin, two 10 mL syringesTwo syringes in a 90° V on one crank pin: the alpha with no displacer, checked s…You might also need
Questions
Why replace the syringe plunger in a Stirling engine?
Its rubber seal's friction is larger than the force a small Stirling makes. A lapped printed piston seals by fit alone, like a graphite piston in glass.
How does the con-rod attach to a syringe piston?
The piston has a 5.4 mm fork slot and a Ø3 pin hole: drop a 5 mm thick con-rod (Ross conrod-45 or crank-kit rods) in and push a 3 × 12 dowel through.
Which syringe piston do I print for a 10 mL syringe?
Measure the barrel bore; for the usual 14.5 mm print f008 (Ø14.42), lap to fit, and keep f015 as a spare if the barrel is tight.