# Constant-diameter cam between two rollers in a yoke

> How can a cam drive a yoke both ways without a spring?

- Category: Mechanisms › Cams
- Kind: Hardware
- Basis: Xem Studio design following Brown No. 117 (1868)
- Page: https://xemstudio.com/objects/cam-between-rollers-yoke-mechanism/ · JSON: https://xemstudio.com/api/geometry?object=cam-between-rollers-yoke-mechanism · Plain text: https://xemstudio.com/objects/cam-between-rollers-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

- The cam turns between two rollers carried on one yoke. Its pitch curve has a constant diameter (opposite radii always add to the roller spacing), so both rollers stay in contact all round and the yoke is pushed one way by one roller's side of the cam and back by the other's.
- Pitch curve r = 22 + 6 sin θ − sin 3θ, rollers Ø10 (623 bearings on Ø3 pins) 44 mm apart: stroke 14 mm per turn. Drawn at 35°: yoke -2.48 mm from centre, both rollers touching.
- Brown's No. 117 (a cam between two rollers in a yoke working a slide-valve rod).
- Parts (each has its own page): constant-diameter-cam-c22-a6-b1-bore8, two-roller-cam-yoke-44-rods-8, ball-bearings-metric, dowel-pins-metric, linear-shafts-h6.
- Brown's movement No. 117 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

## Sizes

| parameter | value |
|---|---|
| pitch curve | 22 + 6 sin θ − sin 3θ |
| roller spacing | 44 mm |
| stroke | 14 mm |
| rollers | 623 bearings |

## 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. 117: figure, his text and an animation](https://507movements.com/mm_117.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/cam-between-rollers-yoke-mechanism/index.json · license: https://xemstudio.com/files/hardware/cam-between-rollers-yoke-mechanism/LICENSE.md

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

## Questions

**How can a cam drive a yoke both ways without a spring?**

The cam turns between two rollers carried on one yoke. Its pitch curve has a constant diameter (opposite radii always add to the roller spacing), so both rollers stay in contact all round and the yoke is pushed one way by one roller's side of the cam and back by the other's.

## Fits with

- [Constant-diameter cam for two Ø10 rollers 44 mm apart, 4 thick, Ø8 bore](https://xemstudio.com/objects/constant-diameter-cam-c22-a6-b1-bore8/)
- [Two-roller cam yoke, roller pins 44 mm apart, 8 × 8 rods](https://xemstudio.com/objects/two-roller-cam-yoke-44-rods-8/)
- [Ball bearings, 683 to 6210 and flanged F6xx (ISO 15)](https://xemstudio.com/objects/ball-bearings-metric/)
- [Dowel pins, 2–6 mm (ISO 2338 / DIN 6325)](https://xemstudio.com/objects/dowel-pins-metric/)
- [Linear shafts Ø3 to Ø25 mm (h6), 100 to 1000 mm long](https://xemstudio.com/objects/linear-shafts-h6/)