Tri-clamp free-piston kit: flexure head, stack ring, hub collars and piston plug for 1.5, 2 and 3 in spools — dimension sheet Source: Xem Studio, https://xemstudio.com/objects/tri-clamp-free-piston-kit/ (CC BY 4.0) Basis: Spiral flexure entry (Ø60/80/100 leaves, 3 rim holes, hub Ø13.2/17.6/22); tri-clamp piston entry (-rod variants); Sunpower / NASA layout: displacer rod through the piston, both suspended on planar spring stacks at the cold end Catalog version: 2026-10-20 Sizes: see table below - Layout, cold end outward: hot cup → spool with the displacer and the -rod piston in it → flexure head (clamps on the spool's open ferrule with a stock clamp) carrying stack A on the piston's tube rod → three M3 standoffs → flexure ring carrying stack B on the displacer rod. Nothing touches but the clearance seals: piston in the bore, displacer rod in the piston's bushing. - Piston side: print the -rod piston, press a dry 3 × 5 × 6 bushing in its crown, drop the piston plug into the skirt and push the two Ø3 × 16 wrist dowels through bosses and plug legs (the bore retains the dowels). Press a 5 mm K&S brass tube into the plug socket (CA): that is the piston rod. Stack A = hub collar b5 · leaf · hub washer · leaf · hub collar b5 on the tube (Ø100 leaves have a Ø8 hub bore: put the hub-bush-100-b5 on the tube first), rim bolted to the head with the clamp plate and spacer from the flexure entry. - Displacer side: Ø3 rod from the displacer cap (M3 grub) through the piston bushing, up the inside of the tube, to stack B on the ring: hub collar b3 · leaf · washer · leaf · collar b3, all on the hub-bush b3 so the leaves' Ø5/Ø8 hub bores are centred on the Ø3 rod. Rod length = spool + head + standoffs. - Stack B height sets the displacer phase mass: 30–40 mm standoffs. Tune: each moving assembly resonates at f = (1/2π)√(k/m); the displacer should run 60–90° ahead of the piston, which you get by making the displacer resonance a little above the piston's (stiffer stack or lighter displacer). - Power take-off: the linear alternator's housing bolts to the flexure head over stack A, and its two-row magnet mover clamps the same 5 mm tube. - Bounce space: with the head open the piston's back side is atmosphere and the engine is a low-pressure demonstrator. For a sealed bounce space put a tri-clamp cup over the whole drive on a longer spool section; the flexure head is then inside the vessel. - LES: the free-piston test bed in tri-clamp. spool bore_mm flexure_od hub_mm tube_rod_mm displacer_rod_mm plate_od plug_pin_z_mm 1.5 34.8 60 13.2 5 3 76 17.6 2 47.5 80 17.6 5 3 96 23.5 3 72.9 100 22.0 5 3 116 37.0 Files elsewhere (not hosted by Xem Studio; license as stated by the publisher): - NASA NTRS: Free-piston Stirling convertor flexure bearing development and life testing — pdf — US Government work — https://ntrs.nasa.gov/citations/20050182933 - Long Earth Society: Tri-clamp Stirling engine builds — web, video — LES site — https://longearthsociety.com/engineering/ - Wikipedia: Free-piston engine — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Free-piston_engine Free files (CC BY 4.0, Xem Studio; STEP + STL, 19 parts): https://xemstudio.com/files/hardware/tri-clamp-free-piston-kit/index.json API: https://xemstudio.com/api/geometry?object=tri-clamp-free-piston-kit