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LTD Stirling displacer Ø96 × 8 and Ø146 × 8
What size displacer goes in a coffee-cup Stirling engine? · Hardware · basis: Senft LTD rule: displacer diameter ≫ stroke; diameter = chamber bore − 4 (2 mm radial gap, designed)
Long Earth Society build part. The warm-hand demonstrator. The engines
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. Mating features
- sizes
- 2 in table
Notes
- The wide, thin displacer of the LTD engine: a solid disc Ø96 × 8 for the Ø100 chamber or Ø146 × 8 for the Ø150, with a Ø2 hole at x −5 (under the top plate's rod guide) for the 2 mm rod.
- The 2 mm radial gap to the chamber wall is designed: air passes round the edge as the displacer moves.
- In the 20 mm chamber it moves 10 mm; at Ø96 that sweeps about 72 mL.
Sizes
| file | diameter | thickness | chamber | radial gap | rod hole |
|---|---|---|---|---|---|
| ltd-100-displacer | 96 | 8 | 100 | 2 | 2 |
| ltd-150-displacer | 146 | 8 | 150 | 2 | 2 |
Mating features
Drawn at the exact size. Open press, slide, run and socket features by your process's clearance; leave designed gaps and clamp fits as drawn.
| feature | exact | mates with | fit | files |
|---|---|---|---|---|
| displacer rod hole | Ø2 | 2 mm rod | press | ltd-100-displacer* |
| displacer rod hole | Ø2 | 2 mm rod | press | ltd-150-displacer* |
| displacer to chamber gap | 2 radial (Ø D−4 in Ø D) | chamber ring bore | designed | ltd-100-displacer* |
| displacer to chamber gap | 2 radial (Ø D−4 in Ø D) | chamber ring bore | designed | ltd-150-displacer* |
Where the files are
Other publishers' files are linked, not hosted. "verify" = check the license at the link before commercial use.
| Wikipedia | Stirling engine | web | CC BY-SA 4.0 (text) |
| James R. Senft | An Introduction to Low Temperature Differential Stirling Engines | book | Moriya Press verify |
| Long Earth Society | Engine builds | web, video | LES site |
Free files
★ Free files 2 parts. Generated by Xem Studio from the standard; threads are plain cylinders at major diameter. CC BY 4.0. index.json
| ltd-100-displacer | displacer Ø96 × 8 with a Ø2 rod hole at x -5 under the top plate's guide (2 mm radial gap to the Ø100 chamber: designed) | STEP · STL |
| ltd-150-displacer | displacer Ø146 × 8 with a Ø2 rod hole at x -5 under the top plate's guide (2 mm radial gap to the Ø150 chamber: designed) | STEP · STL |
Plain text: sheet.txt · JSON: /api/geometry?object=ltd-displacer
How it fits
Goes in or on
LTD Stirling chamber ring, Ø100 and Ø150 × 20inside the Ø100 / Ø150 bore, 2 mm radial gapConnects to
LTD Stirling top plate with syringe socket, Ø120…its 2 mm rod runs in the top plate's Ø2 boreAlso needed
Hobby brass tube, 1/16–21/32 in and 1–12 mm,…2 mm rod in the Ø2 holeIn these build lists
LTD coffee-cup engineRuns on a cup of coffee: wide thin displacer, small piston.You might also need
Questions
What size displacer for a coffee cup Stirling engine?
Ø96 × 8 in a Ø100 × 20 chamber at 10 mm stroke on the engine here; Ø146 × 8 in the Ø150 chamber.
Why is an LTD displacer so wide and thin?
With a 15–20 K difference the pressure swing is small, so it needs a large area moved a short way with little friction.