Planar spiral flexure bearing leaves: Ø40 to Ø120, 3-arm and 2-arm, 0.5 and 2 mm — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/spiral-flexure-bearing/  (CC BY 4.0)
Basis: Archimedean planar springs as on Sunpower / NASA free-piston Stirling convertors; hub Ø = max(bore + 8, 0.22 OD), rim 0.12 OD, arms sweep 330° (2-arm 350°)
Catalog version: 2026-10-20

Sizes: see table below
- A flexure bearing leaf: a flat spring with a hub, spiral arms and a rim. Stacked leaves let a piston move axially while holding it on centre, so it runs in a clearance seal with no contact.
- Sizes Ø40, 60, 80, 100, 120. Each has a 3-arm leaf 0.5 mm thick (with a DXF), the same 3-arm leaf 2.0 mm thick, and a 2-arm leaf 0.5 mm thick (with a DXF). 3-arm arms sweep 330°, 2-arm 350°, from the hub to the rim.
- Hub Ø12 / 13.2 / 17.6 / 22 / 26.4 with bore Ø4 / 5 / 5 / 8 / 8; rim width 0.12 × OD; three Ø3.2 rim holes on a circle 0.88 × OD.
- Axial stiffness per leaf scales with E·t³·w / L³ (L = arm length), so the 2.0 mm leaf is 64 times the 0.5 mm leaf in the same material. Natural frequency of the suspended mass: f = (1/2π)√(k/m).
- Three arms give equal radial stiffness in every direction; two-arm leaves are softer axially but let the hub tilt.

od_mm  hub_mm  rim_mm  arm_w_mm  bore_mm  arm_radial_span_mm  rim_hole_circle_mm
40  12  4.8  1.6  4  9.2  35.2
60  13.2  7.2  2.0  5  16.2  52.8
80  17.6  9.6  2.5  5  21.6  70.4
100  22.0  12.0  3.0  8  27.0  88.0
120  26.4  14.4  3.5  8  32.4  105.6

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- NASA (NTRS, public domain): Free-piston Stirling convertor flexure bearing development and life testing (2005) — PDF — US Government work, public domain — https://ntrs.nasa.gov/search?q=20050182933
- NASA (NTRS, public domain): Flexure bearing design for free-piston Stirling engines (1986) — PDF — US Government work, public domain — https://ntrs.nasa.gov/search?q=19860020334
- NASA (NTRS, public domain): Advanced Stirling Radioisotope Generator (ASRG) engineering unit (2011) — PDF — US Government work, public domain — https://ntrs.nasa.gov/search?q=20110016393
- Wikipedia: Flexure bearing — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Flexure_bearing
- Sunpower (AMETEK): Free-piston Stirling technology overview — web — Sunpower site [verify license at link] — https://sunpowerinc.com/
- Long Earth Society: Engine builds — web, video — LES site — https://longearthsociety.com/engineering/

Free files (CC BY 4.0, Xem Studio; STEP + STL, 15 parts): https://xemstudio.com/files/hardware/spiral-flexure-bearing/index.json
API: https://xemstudio.com/api/geometry?object=spiral-flexure-bearing