# Wheel for a face spiral, module 1.5, 24 teeth, generated by the scroll at radius 39

> What wheel runs on a face spiral?

- Category: Mechanisms › Gears
- Kind: Modern device
- Basis: Xem Studio design following Brown's figure (1868); true size, no printing allowance
- Page: https://xemstudio.com/objects/face-spiral-wheel-m1-5-24t-for-scroll-r39/ · JSON: https://xemstudio.com/api/geometry?object=face-spiral-wheel-m1-5-24t-for-scroll-r39 · Plain text: https://xemstudio.com/objects/face-spiral-wheel-m1-5-24t-for-scroll-r39/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/)

## Overall (mm)

| length | width | height |
|---|---|---|
| 38.85 | 38.85 | 8.0 |

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

## Notes

- 24-tooth wheel of module 1.5 (pitch Ø36, tip Ø39, root Ø32.25, 8 mm face, Ø6 bore) whose teeth were generated by the spiral rib itself: in every plane across the face the rib's section (a rack tooth that is slightly wider and farther out away from the disc's centre line) was swept past the turning wheel and the envelope taken, then the seven sections lofted (spline fit within 0.108 mm). The result is an involute-like tooth that is very slightly curved and thinner across the face — the exact mate of the rib at radius 39, where a plain straight spur gear would bind at the face edges.
- One tooth per turn of the disc; the wheel's axis lies parallel to the disc face, tangent to the spiral at the mesh.
- Xem Studio design following Brown's figure; true size, no printing allowance (apply your own to the mating features).

## Sizes

| dimension | value |
|---|---|
| module | 1.5 |
| teeth | 24 |
| pitch Ø | 36 mm |
| tip / root Ø | 39 / 32.25 mm |
| face | 8 mm |
| bore | Ø6 |
| mesh radius on the disc | 39 mm |

## 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. 29: figure, his text and an animation](https://507movements.com/mm_029.html) — web — Publisher's page; dimensions are facts
- Xem Studio: [drawing](https://xemstudio.com/objects/face-spiral-disc-and-wheel-mechanism/) — web — Publisher's page; dimensions are facts

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

Index: https://xemstudio.com/files/hardware/face-spiral-wheel-m1-5-24t-for-scroll-r39/index.json · license: https://xemstudio.com/files/hardware/face-spiral-wheel-m1-5-24t-for-scroll-r39/LICENSE.md

- face-spiral-wheel-m1-5-24t-for-scroll-r39: [STEP](https://xemstudio.com/files/hardware/face-spiral-wheel-m1-5-24t-for-scroll-r39/face-spiral-wheel-m1-5-24t-for-scroll-r39.step) · [STL](https://xemstudio.com/files/hardware/face-spiral-wheel-m1-5-24t-for-scroll-r39/face-spiral-wheel-m1-5-24t-for-scroll-r39.stl) — wheel, axis Z, z -4..4, a space centred on +X

## Questions

**What wheel runs on a face spiral?**

24-tooth wheel of module 1.5 (pitch Ø36, tip Ø39, root Ø32.25, 8 mm face, Ø6 bore) whose teeth were generated by the spiral rib itself: in every plane across the face the rib's section (a rack tooth that is slightly wider and farther out away from the disc's centre line) was swept past the turning wheel and the envelope taken, then the seven sections lofted (spline fit within 0.108 mm). The result is an involute-like tooth that is very slightly curved and thinner across the face — the exact mate of the rib at radius 39, where a plain straight spur gear would bind at the face edges.

## Fits with

- [Face spiral (scroll) on a disc turning a wheel one tooth per turn (24 : 1)](https://xemstudio.com/objects/face-spiral-disc-and-wheel-mechanism/)