# Heart cam with roller follower (uniform motion)

> Why is a heart cam heart-shaped?

- Category: Mechanisms › Cams
- Kind: Hardware
- Basis: Xem Studio drawing; classic mechanism (Brown No. 96)
- Page: https://xemstudio.com/objects/heart-cam-mechanism/ · JSON: https://xemstudio.com/api/geometry?object=heart-cam-mechanism · Plain text: https://xemstudio.com/objects/heart-cam-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

- Radius = r₀ + h·θ/180° on the way out and back on the way in: equal angle steps give equal lift steps, so the follower moves at a constant speed (20 mm each way per turn here).
- The cusp at the top and the dip at the bottom are where direction reverses (infinite acceleration in theory): fine for slow traverse, e.g. thread winding.
- A roller follower's pitch curve is the profile offset by the roller radius; this file is the pitch-correct profile for a knife-edge follower — offset by 5 mm for the Ø10 roller.
- Parts (each has its own page): heart-cam-r15-h20, roller-follower-10, crosshead-guide-8mm. Brown's movement No. 96 shows it (1868).

## Sizes

| parameter | value |
|---|---|
| base radius r₀ | 15 mm |
| lift h | 20 mm |
| motion | uniform velocity |

## 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

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

Index: https://xemstudio.com/files/hardware/heart-cam-mechanism/index.json

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

## Questions

**Why is a heart cam heart-shaped?**

Radius = r₀ + h·θ/180° on the way out and back on the way in: equal angle steps give equal lift steps, so the follower moves at a constant speed (20 mm each way per turn here).

## Fits with

- [Heart cam, base radius 15, lift 20 mm](https://xemstudio.com/objects/heart-cam-r15-h20/)
- [Roller follower Ø10 on a Ø3 pin](https://xemstudio.com/objects/roller-follower-10/)
- [Crosshead guide, Ø8 bore × 30](https://xemstudio.com/objects/crosshead-guide-8mm/)