# Face spiral (scroll) disc, pitch 4.71 (module 1.5), r 30 → 48.85, Ø104 × 6

> What is a face spiral disc?

- 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-disc-m1-5-r30-4turns-d104/ · JSON: https://xemstudio.com/api/geometry?object=face-spiral-disc-m1-5-r30-4turns-d104 · Plain text: https://xemstudio.com/objects/face-spiral-disc-m1-5-r30-4turns-d104/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 |
|---|---|---|
| 104.0 | 104.0 | 9.38 |

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

## Notes

- A Ø104 × 6 disc with one raised Archimedean spiral rib on its face: radial pitch p = π m = 4.71 mm, from radius 30 to 48.85 (4 turns), Ø8 bore. The rib's radial section is the basic rack of module 1.5 (20° flanks, πm/2 thick at its pitch height 1.88 mm above the face, top at 3.38 mm): seen by a toothed part standing over the face, the rib is a rack that advances p per turn of the disc — a worm unrolled onto a face.
- Swept along the spiral with the profile kept upright and normal to the path; the bottom of the rib runs 0.5 mm into the disc so it is one solid.
- Xem Studio design following Brown's figure; true size, no printing allowance (apply your own to the mating features).

## Sizes

| dimension | value |
|---|---|
| pitch p | 4.71 mm (module 1.5) |
| spiral | r 30 → 48.85, 4 turns |
| rib height | 3.38 mm above the face |
| disc | Ø104 × 6 |
| bore | Ø8 |

## 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-disc-m1-5-r30-4turns-d104/index.json · license: https://xemstudio.com/files/hardware/face-spiral-disc-m1-5-r30-4turns-d104/LICENSE.md

- face-spiral-disc-m1-5-r30-4turns-d104: [STEP](https://xemstudio.com/files/hardware/face-spiral-disc-m1-5-r30-4turns-d104/face-spiral-disc-m1-5-r30-4turns-d104.step) · [STL](https://xemstudio.com/files/hardware/face-spiral-disc-m1-5-r30-4turns-d104/face-spiral-disc-m1-5-r30-4turns-d104.stl) — disc, axis Z, face at z = 0, rib up to z = 3.38

## Questions

**What is a face spiral disc?**

A Ø104 × 6 disc with one raised Archimedean spiral rib on its face: radial pitch p = π m = 4.71 mm, from radius 30 to 48.85 (4 turns), Ø8 bore. The rib's radial section is the basic rack of module 1.5 (20° flanks, πm/2 thick at its pitch height 1.88 mm above the face, top at 3.38 mm): seen by a toothed part standing over the face, the rib is a rack that advances p per turn of the disc — a worm unrolled onto a face.

## 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/)