Treadle and crank (crank-rocker four-bar) — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/treadle-crank-mechanism/  (CC BY 4.0)
Basis: Xem Studio design following Brown No. 158 (1868)
Catalog version: 2026-10-20

Sizes: see table below
- A foot treadle rocking on a pivot drives a crank round through a connecting rod: a crank-rocker four-bar. Because the crank is the shortest link and next to the frame (Grashof: s + l ≤ p + q), it turns fully while the treadle only rocks.
- Here crank 20, rod 80, treadle 100 and frame 100 mm (catalog four-bar links): the treadle swings 25.08° per crank turn; a flywheel carries the crank through the two dead points where rod and crank line up.
- Brown's No. 158 (treadle driving a disc or crank), the drive of foot lathes, grinders and sewing machines.
- Parts (each has its own page): four-bar-links, dowel-pins-metric.
- Brown's movement No. 158 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

parameter  value
crank  20 mm
connecting rod  80 mm
treadle  100 mm
frame  100 mm
treadle swing  25.08°

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- Henry T. Brown (1868, public domain): Five Hundred and Seven Mechanical Movements — scan on archive.org — web — Publisher's page; dimensions are facts — https://archive.org/details/fivehundredseven00browiala
- 507movements.com: Brown's movement No. 158: figure, his text and an animation — web — Publisher's page; dimensions are facts — https://507movements.com/mm_158.html

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