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Rhombic drive crank gear, module 1.5, 44 T, 7 mm throw
What are the dimensions of the crank gears in a rhombic drive? · Hardware · basis: Involute spur gear module 1.5, 44 teeth, 20° pressure angle (pitch Ø66); two of them on 66 mm centres; crank pin at e = 7, a quarter tooth pitch off a tooth centre; rhombic kinematics in tools/rhombic_geom.py
Long Earth Society build part. The balanced beta drive for the 2 in tri-clamp engine; the rhombic frame head in the linkage fittings carries it on the spool. 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
- 9 in table
Notes
- The two counter-rotating gears of the rhombic drive are this one part used twice: module 1.5, 44 teeth, pitch Ø66, tip Ø69, 6 face, Ø12 × 5 hub with an M3 grub (Ø2.5 tapped), Ø5 bore (fit: slide).
- Crank-pin hole Ø3 (fit: press) at 7 mm from the axis and 2.045° (a quarter tooth pitch) from a tooth centre. With the two gears mirror images of each other (both pins at the same height), a tooth of one then sits in a gap of the other on the 66 mm centre line: the pin layout and the mesh agree.
- With the 30 mm links and yoke pivots at ±12.7 the displacer leads the piston by 90.0° and both strokes are 20.12 mm.
Sizes
| parameter | value |
|---|---|
| module | 1.5 |
| teeth | 44 |
| pitch Ø | 66.0 |
| tip Ø | 69.0 |
| face width | 6.0 |
| hub | Ø12 × 5 |
| bore | Ø5 |
| crank pin | Ø3 at 7, 2.045° off a tooth |
| gear centres | 66.0 |
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 |
|---|---|---|---|---|
| gear bore | Ø5 | Ø5 gear shaft | slide | crank-gear-* |
| gear crank-pin hole | Ø3 | Ø3 crank pin | press | crank-gear-* |
| gear hub grub hole | Ø2.5 | M3 tap drill | designed | crank-gear-* |
| gear teeth | module 1.5, 44 T, 20°, on 66 mm centres | the other crank gear (no backlash drawn) | run | crank-gear-* |
Where the files are
Other publishers' files are linked, not hosted. "verify" = check the license at the link before commercial use.
| Wikipedia | Rhombic drive | web | CC BY-SA 4.0 (text) |
| Wikipedia | Stirling engine | web | CC BY-SA 4.0 (text) |
| Philips Research / Meijer | The Philips Stirling engine (rhombic drive papers, 1958–1965) | web | reference verify |
| Long Earth Society | Engine builds | web, video | LES site |
Free files
★ Free files 1 parts. Generated by Xem Studio from the standard; threads are plain cylinders at major diameter. CC BY 4.0. index.json
| crank-gear-m1.5-44t-e7 | crank gear module 1.5, 44 teeth (Ø66 pitch, Ø69 tip), 6 face, Ø12 × 5 hub with an M3 grub (Ø2.5 tapped), Ø5 bore, Ø3 crank-pin hole at 7 mm, 2.045° (a quarter tooth pitch) off a tooth centre; two per drive, meshed on 66 mm centres | STEP · STL |
Plain text: sheet.txt · JSON: /api/geometry?object=rhombic-crank-gear
How it fits
Goes in or on
Rhombic frame head for the 2 in tri-clamp betaØ5 gear shafts in the head's 625s, 66 mm centresConnects to
Rhombic drive crank pin Ø3 × 17Ø3 pin pressed in the gear at 7 mm
Rhombic drive link, 30 mm centrestwo links ride each crank pinAlternatives
Spur gears, involute 20°other involute gearsAlso needed
Crankshafts Ø3, Ø5 and Ø8 with full-length D-flatØ5 gear shaftsIn these build lists
Beta Stirling, rhombic drive, 2 in tri-clampDisplacer and piston in one bore, driven by two counter-rotating gears on a rhom…You might also need
Questions
What gears does a rhombic drive use?
Two identical spur gears turning opposite ways; here module 1.5, 44 T on 66 mm centres, each with a crank pin at 7 mm.
How are the rhombic gears timed?
Mesh them with the two crank pins level and mirror images of each other; the pin hole sits a quarter tooth pitch off a tooth so that position meshes.
What stroke do these gears give?
20.12 mm on both yokes with the 30 mm links (about 2√2 × the 7 mm throw at a 90° phase).