# Crank pin in a slotted bell crank

> How does a crank rock a bell crank?

- Category: Mechanisms › Linkages
- Kind: Hardware
- Basis: Xem Studio design following Brown No. 156 (1868)
- Page: https://xemstudio.com/objects/crank-slotted-bell-crank-mechanism/ · JSON: https://xemstudio.com/api/geometry?object=crank-slotted-bell-crank-mechanism · Plain text: https://xemstudio.com/objects/crank-slotted-bell-crank-mechanism/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); files Xem Studio Design License (free to use and sell from, not to redistribute as files: https://xemstudio.com/license/)
- 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 crank pin, in a slide block, runs in a slot along one arm of a bell crank pivoted 70 mm from the crank centre: the bell crank rocks through ±9.87° (sin⁻¹ 12/70), with the quick-return timing of a slotted lever, and its second arm, 50 mm long at 90°, carries the motion off at a right angle.
- Drawn at crank angle 200°: bell crank at 9.71°, output pin at (49.28, 8.43).
- Brown's No. 156 (crank pin working in a slotted bell crank).
- Parts (each has its own page): slotted-bell-crank-100-50-slot-50-90-b5, crank-disc-36-pin-r12, slide-block-12x6, dowel-pins-metric.
- Brown's movement No. 156 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

## Sizes

| parameter | value |
|---|---|
| crank radius | 12 mm |
| pivot distance | 70 mm |
| swing | ±9.87° |
| output arm | 50 mm at 90° |

## 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. 156: figure, his text and an animation](https://507movements.com/mm_156.html) — web — Publisher's page; dimensions are facts

## Free STEP/STL (1 parts, Xem Studio Design License, Xem Studio)

Index: https://xemstudio.com/files/hardware/crank-slotted-bell-crank-mechanism/index.json · license: https://xemstudio.com/files/hardware/crank-slotted-bell-crank-mechanism/LICENSE.md

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

## Questions

**How does a crank rock a bell crank?**

A crank pin, in a slide block, runs in a slot along one arm of a bell crank pivoted 70 mm from the crank centre: the bell crank rocks through ±9.87° (sin⁻¹ 12/70), with the quick-return timing of a slotted lever, and its second arm, 50 mm long at 90°, carries the motion off at a right angle.

## Fits with

- [Slotted bell crank: 100 mm arm with a 6.4 slot (50–90 mm) and a 50 mm arm at 90°, Ø5 bore](https://xemstudio.com/objects/slotted-bell-crank-100-50-slot-50-90-b5/)
- [Crank disc Ø36 × 5, Ø5 bore, Ø3 pin hole at 12 mm](https://xemstudio.com/objects/crank-disc-36-pin-r12/)
- [Slide block 12 × 6.2 mm for a 6.4 mm slot](https://xemstudio.com/objects/slide-block-12x6/)
- [Dowel pins, 2–6 mm (ISO 2338 / DIN 6325)](https://xemstudio.com/objects/dowel-pins-metric/)