Rhombic drive crank gear, module 1.5, 44 T, 7 mm throw — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/rhombic-crank-gear/  (CC BY 4.0)
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
Catalog version: 2026-10-20

Sizes: see table below
- 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.

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

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-crank-gear/index.json
API: https://xemstudio.com/api/geometry?object=rhombic-crank-gear