Inner crank webs for the tri-clamp cross gamma: two throws 90° apart on a Ø3 shaft — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/tri-clamp-cross-crank-webs/  (CC BY 4.0)
Basis: Design values: 6 mm throws (12 mm strokes), Ø3 pins and shaft, 623 con-rod eyes (R7)
Catalog version: 2026-10-20

Sizes: see table below
- A built-up crank small enough to turn inside a Ø29 chamber in the middle of the cross. The hub web goes on the end of the Ø3 shaft (M3 grub); a Ø3 × 12 dowel pressed through its disc is the diaphragm crank pin; the con-rod for the diaphragm turns on it; the link web is pressed on the pin's far end.
- The link web carries the displacer pin, a second Ø3 × 12 dowel, 90° on from the diaphragm pin. Each pin passes only through its own con-rod: the shaft stops in the hub web, the diaphragm pin stops in the link web, the displacer pin starts there, so no con-rod eye ever meets another pin.
- Both throws are 6 mm. The con-rod eyes sweep a radius of 13; the webs are Ø20.

file  hub_mm  disc_mm  pins
inner-crank-web-hub-r6  Ø10 × 6, Ø3 bore, M3 grub  Ø20 × 4  1 at r 6
inner-crank-web-link-r6    Ø20 × 5.5  2 at r 6, 90° apart

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- Long Earth Society: Engine builds — web, video — LES site — https://longearthsociety.com/engineering/

Free files (CC BY 4.0, Xem Studio; STEP + STL, 2 parts): https://xemstudio.com/files/hardware/tri-clamp-cross-crank-webs/index.json
API: https://xemstudio.com/api/geometry?object=tri-clamp-cross-crank-webs