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Flexure hub collars: split collars Ø13.2, Ø17.6 and Ø22 for Ø3 rod and Ø5 tube
How do I clamp a flexure leaf hub onto a piston rod? · Hardware · basis: Collar Ø = flexure hub Ø (max(bore + 8, 0.22 × OD)); 6 mm thick so the M3 pinch screw's head (Ø5.5) stays within it; 0.8 mm slit; M3 pinch (Ø2.5)
Long Earth Society build part. The connecting parts of the tri-clamp free-piston engine. 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
- 3 in table
Notes
- A split clamping collar the size of a flexure leaf's hub: two per stack, one each end, squeeze the leaves, hub washers and spacers onto the rod.
- Ø13.2 (for Ø60 leaves), Ø17.6 (Ø80) and Ø22 (Ø100), all 6 mm thick. b5 collars have a Ø5 bore for the 5 mm tube piston rod; b3 collars a Ø3 bore for the displacer rod.
- A 0.8 mm slit runs from the bore to the rim, closed by an M3 × 10 screw in a Ø2.5 tangential hole at mid-thickness; the screw head stays inside the collar's 6 mm, clear of the leaf beside it.
Sizes
| flexure_od_mm | collar_od_mm | bore_mm | thickness_mm | slit_mm | pinch |
|---|---|---|---|---|---|
| 60 | 13.2 | 5 / 3 | 6 | 0.8 | M3 (Ø2.5) |
| 80 | 17.6 | 5 / 3 | 6 | 0.8 | M3 (Ø2.5) |
| 100 | 22.0 | 5 / 3 | 6 | 0.8 | M3 (Ø2.5) |
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 |
|---|---|---|---|---|
| hub collar bore (b5 / b3) | Ø5 / Ø3 | 5 mm tube / Ø3 rod | slide | hub-collar-* |
| hub-collar slit | 0.8 | closes on the tube / rod | clamp | hub-collar-* |
| hub-collar pinch hole | Ø2.5 | M3 tap drill | designed | hub-collar-* |
Where the files are
Other publishers' files are linked, not hosted. "verify" = check the license at the link before commercial use.
| NASA NTRS | Free-piston Stirling convertor flexure bearing development and life testing | US Government work | |
| Long Earth Society | Tri-clamp Stirling engine builds | web, video | LES site |
| Wikipedia | Free-piston engine | web | CC BY-SA 4.0 (text) |
Free files
★ Free files 6 parts. Generated by Xem Studio from the standard; threads are plain cylinders at major diameter. CC BY 4.0. index.json
| hub-collar-60-b5 | split hub collar Ø13.2 × 6, Ø5 bore, 0.8 slit, M3 pinch (Ø2.5 tapped) across the slit at mid-thickness: clamps the leaf hubs on the 5 mm tube rod (two per stack) | STEP · STL |
| hub-collar-60-b3 | split hub collar Ø13.2 × 6, Ø3 bore, 0.8 slit, M3 pinch (Ø2.5 tapped) across the slit at mid-thickness: clamps the leaf hubs on the Ø3 displacer rod (two per stack) | STEP · STL |
| hub-collar-80-b5 | split hub collar Ø17.6 × 6, Ø5 bore, 0.8 slit, M3 pinch (Ø2.5 tapped) across the slit at mid-thickness: clamps the leaf hubs on the 5 mm tube rod (two per stack) | STEP · STL |
| hub-collar-80-b3 | split hub collar Ø17.6 × 6, Ø3 bore, 0.8 slit, M3 pinch (Ø2.5 tapped) across the slit at mid-thickness: clamps the leaf hubs on the Ø3 displacer rod (two per stack) | STEP · STL |
| hub-collar-100-b5 | split hub collar Ø22 × 6, Ø5 bore, 0.8 slit, M3 pinch (Ø2.5 tapped) across the slit at mid-thickness: clamps the leaf hubs on the 5 mm tube rod (two per stack) | STEP · STL |
| hub-collar-100-b3 | split hub collar Ø22 × 6, Ø3 bore, 0.8 slit, M3 pinch (Ø2.5 tapped) across the slit at mid-thickness: clamps the leaf hubs on the Ø3 displacer rod (two per stack) | STEP · STL |
Plain text: sheet.txt · JSON: /api/geometry?object=flexure-hub-collar
How it fits
Goes in or on
Planar spiral flexure bearing leavesone each end of the leaf stack on the hubConnects to
Tri-clamp piston plugb5 collar on the 5 mm tube from the plug
Flexure hub centring bushcollars clamp the stack on the bushAlso needed
Socket head cap screws, M2–M8M3 pinch screwIn these build lists
Free-piston Stirling, 2 in tri-clampNo crank: piston and displacer each hang on a stack of spiral flexures, with a t…You might also need
Questions
How is a flexure leaf fixed to the rod?
Between two split hub collars the size of the leaf's hub, pinched onto the rod with an M3 screw across a 0.8 mm slit.
Which collar for the piston rod?
The b5 collar (Ø5 bore) on the 5 mm tube; b3 (Ø3 bore) on the displacer rod.