Rhombic drive lower yoke, 25.4 mm pivot span — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/rhombic-lower-yoke/  (CC BY 4.0)
Basis: Yoke pivots at ±12.7 (rhombic kinematics, tools/rhombic_geom.py), pivot axes parallel to the gear shafts, rod axis across them; bore at the rod, M3 tap drill Ø2.5
Catalog version: 2026-10-20

Sizes: see table below
- The lower yoke of the rhombus: a 35.4 × 10 bar, 6 thick along the gear-shaft direction, with Ø3 pivot holes (fit: run) at ±12.7 running parallel to the gear shafts.
- A Ø13 × 16 boss on the rod axis (across the pivots) holds the 5 mm tube piston rod (Ø5 bore through; the Ø3 displacer rod runs on up inside it) (fit: slide), with an M3 grub (Ø2.5 tapped) entering at mid-height; an M3 × 4 grub sits flush.
- Both yokes sit in one plane on the rod axis, in front of the two link planes; the lower-yoke pivot pins are Ø3 × 16.

parameter  value
pivot span  25.4
bar  35.4 × 10 × 6
pivots  2 × Ø3 (run), along the gear-shaft direction
boss  Ø13 × 16
rod bore  Ø5 through
grub hole  Ø2.5 (M3)

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- Wikipedia: Rhombic drive — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Rhombic_drive
- Wikipedia: Stirling engine — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Stirling_engine
- Philips Research / Meijer: The Philips Stirling engine (rhombic drive papers, 1958–1965) — web — reference [verify license at link] — https://en.wikipedia.org/wiki/Rhombic_drive#History
- Long Earth Society: Engine builds — web, video — LES site — https://longearthsociety.com/engineering/

Free files (CC BY 4.0, Xem Studio; STEP + STL, 1 parts): https://xemstudio.com/files/hardware/rhombic-lower-yoke/index.json
API: https://xemstudio.com/api/geometry?object=rhombic-lower-yoke