# Treadle and crank (crank-rocker four-bar)

> How does a treadle turn a wheel?

- Category: Mechanisms › Linkages
- Kind: Hardware
- Basis: Xem Studio design following Brown No. 158 (1868)
- Page: https://xemstudio.com/objects/treadle-crank-mechanism/ · JSON: https://xemstudio.com/api/geometry?object=treadle-crank-mechanism · Plain text: https://xemstudio.com/objects/treadle-crank-mechanism/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); linked files under their publishers' licenses
- Use in every chat: add https://xemstudio.com/mcp as a connector (https://xemstudio.com/use-with-ai/)

**Exact dimensions.** True size, with no printing tolerance added.

## Notes

- 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.

## Sizes

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

## Where the files are

- Henry T. Brown (1868, public domain): [Five Hundred and Seven Mechanical Movements — scan on archive.org](https://archive.org/details/fivehundredseven00browiala) — web — Publisher's page; dimensions are facts
- 507movements.com: [Brown's movement No. 158: figure, his text and an animation](https://507movements.com/mm_158.html) — web — Publisher's page; dimensions are facts

## Free STEP/STL (1 parts, CC BY 4.0, Xem Studio)

Index: https://xemstudio.com/files/hardware/treadle-crank-mechanism/index.json

- treadle-crank-mechanism-assembly: [STEP](https://xemstudio.com/files/hardware/treadle-crank-mechanism/treadle-crank-mechanism-assembly.step) · [STL](https://xemstudio.com/files/hardware/treadle-crank-mechanism/treadle-crank-mechanism-assembly.stl) — Assembled mechanism, all parts placed at one pose (STEP keeps each part separate)

## Questions

**How does a treadle turn a wheel?**

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.

## Fits with

- [Four-bar links: flat links with 20 to 100 mm hole centres](https://xemstudio.com/objects/four-bar-links/)
- [Dowel pins, 2–6 mm (ISO 2338 / DIN 6325)](https://xemstudio.com/objects/dowel-pins-metric/)