# Tracer arm, Ø10 hub, Ø3 pin at 15 mm

> What does the tracer arm do?

- Category: Hardware › Mechanism parts
- Kind: Modern device
- Basis: Xem Studio design following Brown's figure (1868); true size, no printing allowance
- Page: https://xemstudio.com/objects/tusi-tracer-arm-15/ · JSON: https://xemstudio.com/api/geometry?object=tusi-tracer-arm-15 · Plain text: https://xemstudio.com/objects/tusi-tracer-arm-15/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/)

## Overall (mm)

| length | width | height |
|---|---|---|
| 33.0 | 18.0 | 5.0 |

**Exact dimensions.** True size, with no printing tolerance added.

## Notes

- Fixed to the planet (same Ø10 axle), it puts a Ø3 pin exactly on the planet's pitch circle (15 mm out): that point runs on a straight line through the ring's centre.
- Xem Studio design following Brown's figure; true size, no printing allowance (apply your own to the mating features).

## Sizes

| dimension | value |
|---|---|
| pin radius | 15 mm |
| hub hole | Ø10 |
| pin hole | Ø3 |

## 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. 329: figure, his text and an animation](https://507movements.com/mm_329.html) — web — Publisher's page; dimensions are facts
- Xem Studio: [drawing](https://xemstudio.com/objects/tusi-couple-straight-line-mechanism/) — web — Publisher's page; dimensions are facts

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

Index: https://xemstudio.com/files/hardware/tusi-tracer-arm-15/index.json

- tusi-tracer-arm-15: [STEP](https://xemstudio.com/files/hardware/tusi-tracer-arm-15/tusi-tracer-arm-15.step) · [STL](https://xemstudio.com/files/hardware/tusi-tracer-arm-15/tusi-tracer-arm-15.stl) — tracer arm, z 0..5

## Questions

**What does the tracer arm do?**

Fixed to the planet (same Ø10 axle), it puts a Ø3 pin exactly on the planet's pitch circle (15 mm out): that point runs on a straight line through the ring's centre.

## Fits with

- [Tusi couple: straight line from a gear rolling inside a ring twice its size](https://xemstudio.com/objects/tusi-couple-straight-line-mechanism/)