# Bell-crank lever turning a pull through 90°

> What does a bell crank do?

- Category: Mechanisms › Linkages
- Kind: Hardware
- Basis: Xem Studio design following Brown No. 126 (1868)
- Page: https://xemstudio.com/objects/bell-crank-lever-mechanism/ · JSON: https://xemstudio.com/api/geometry?object=bell-crank-lever-mechanism · Plain text: https://xemstudio.com/objects/bell-crank-lever-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

- An L-shaped lever on a pivot at its corner: a pull on one arm becomes a pull at right angles on the other. Force ratio = arm lengths (1 : 1 for 30 × 30 mm; the 20 × 40 crank gives 2 : 1).
- Here the catalog 30 × 30 bell crank turns on a 623 bearing pressed in its Ø10 pocket, with 60 mm links on each arm.
- Brown's No. 126; used in bell-pulls, control rods and brakes to change the direction of a push or pull.
- Parts (each has its own page): bell-cranks, ball-bearings-metric, four-bar-links, dowel-pins-metric.
- Brown's movement No. 126 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

## Sizes

| parameter | value |
|---|---|
| arms | 30 × 30 mm at 90° |
| pivot | 623 bearing on Ø3 pin |
| links | 2 × 60 mm |
| ratio | 1 : 1 |

## 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. 126: figure, his text and an animation](https://507movements.com/mm_126.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/bell-crank-lever-mechanism/index.json

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

## Questions

**What does a bell crank do?**

An L-shaped lever on a pivot at its corner: a pull on one arm becomes a pull at right angles on the other. Force ratio = arm lengths (1 : 1 for 30 × 30 mm; the 20 × 40 crank gives 2 : 1).

## Fits with

- [Bell cranks: 30 × 30 and 20 × 40 mm arms at 90°](https://xemstudio.com/objects/bell-cranks/)
- [Ball bearings, 683 to 6210 and flanged F6xx (ISO 15)](https://xemstudio.com/objects/ball-bearings-metric/)
- [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/)