# Constant-breadth cam turning in a yoke (three strokes per turn)

> How does a constant-breadth cam reciprocate a bar?

- Category: Mechanisms › Cams
- Kind: Hardware
- Basis: Xem Studio design following Brown No. 276 (1868)
- Page: https://xemstudio.com/objects/constant-breadth-cam-yoke-mechanism/ · JSON: https://xemstudio.com/api/geometry?object=constant-breadth-cam-yoke-mechanism · Plain text: https://xemstudio.com/objects/constant-breadth-cam-yoke-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 cam of constant breadth (a Reuleaux triangle with rounded corners) turns about its centre between two parallel faces of a yoke exactly its breadth apart, so it touches both at every angle and drives the yoke both ways. Its distance to each face changes from the corner radius to the flank radius: the yoke moves 4.64 mm to and fro three times per turn of the cam.
- Breadth 40 (side 30, corners R5); drawn at 20°, the yoke 2.06 mm from centre.
- Brown's No. 276 (cam giving a reciprocating motion to a bar); the corner-pivoted triangle of No. 91 gives one long stroke with dwells instead.
- Parts (each has its own page): constant-breadth-cam-s30-r5-bore5, constant-breadth-cam-yoke-40, dowel-pins-metric.
- Brown's movement No. 276 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

## Sizes

| parameter | value |
|---|---|
| breadth | 40 mm |
| pivot | centre |
| stroke | 4.64 mm |
| strokes per turn | 3 |

## 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. 276: figure, his text and an animation](https://507movements.com/mm_276.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/constant-breadth-cam-yoke-mechanism/index.json · license: https://xemstudio.com/files/hardware/constant-breadth-cam-yoke-mechanism/LICENSE.md

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

## Questions

**How does a constant-breadth cam reciprocate a bar?**

A cam of constant breadth (a Reuleaux triangle with rounded corners) turns about its centre between two parallel faces of a yoke exactly its breadth apart, so it touches both at every angle and drives the yoke both ways. Its distance to each face changes from the corner radius to the flank radius: the yoke moves 4.64 mm to and fro three times per turn of the cam.

## Fits with

- [Constant-breadth cam: rounded Reuleaux triangle, breadth 40, Ø5 bore at its centre](https://xemstudio.com/objects/constant-breadth-cam-s30-r5-bore5/)
- [Yoke 52 × 62.64 with a 40 mm wide opening and two 8 × 8 rods](https://xemstudio.com/objects/constant-breadth-cam-yoke-40/)
- [Dowel pins, 2–6 mm (ISO 2338 / DIN 6325)](https://xemstudio.com/objects/dowel-pins-metric/)