# Face spiral on a disc as a drill feed: scroll driving a rack

> How does a spiral on a disc give a drill its feed?

- Category: Mechanisms › Screws & feeds
- Kind: Hardware
- Basis: Xem Studio design following Brown No. 99 (1868)
- Page: https://xemstudio.com/objects/face-spiral-rack-feed-mechanism/ · JSON: https://xemstudio.com/api/geometry?object=face-spiral-rack-feed-mechanism · Plain text: https://xemstudio.com/objects/face-spiral-rack-feed-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

- Resize: multiply every length by one factor k and the motion stays identical: angles, ratios, timing and the formulas below do not change, because a mechanism's motion depends only on the ratios of its lengths. Here, scales with k: feed per turn, rack height over the face; stays the same: disc, rack.
- Resize: fit clearances stay in mm (a slide fit is the same gap at any size); keep every printed wall and pin at least two nozzle widths; mass grows with k³ but part strength only with k², so at k = 2 parts are about 8× heavier and 4× stronger: check pins and thin links when scaling up.
- A spiral rib on the face of a disc engages a rack that slides radially over it: every turn of the disc moves the rack one pitch (3.14 mm) outward or inward — a slow, smooth feed from a continuously turning disc, the scroll-chuck principle used for the feed motion of drilling machines (the rack is on the drill's spindle sleeve).
- The rib's radial section is the module 1 basic rack; the feed rack's teeth were generated by the rib across the rack's 8 mm width, so they curve to follow the spiral and mesh without binding. With this 8.4-turn scroll (r 20 → 46.39) the 6-tooth rack stays fully on the rib over about ±3 mm of travel about the drawn position; a longer scroll gives a longer stroke. Checked at six positions over two turns: no overlap beyond contact.
- Brown's No. 99 (spiral guide on the face of a disc, drilling-machine feed). Drawn with the disc turned 90°, the rack's centre 31.78 mm from the disc's axis; the rack's guide is not drawn.
- Parts (each has its own page): face-spiral-disc-m1-r20-8-4turns-d100, face-spiral-feed-rack-m1-6t-w8, linear-shafts-h6.
- Brown's movement No. 99 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

## Sizes

| parameter | value |
|---|---|
| disc | Ø100 × 6, spiral r 20 → 46.39 (8.4 turns) |
| feed per turn | 3.14 mm |
| rack | 6 T, module 1, 19.05 long |
| rack height over the face | pitch line 1.25 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. 99: figure, his text and an animation](https://507movements.com/mm_099.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/face-spiral-rack-feed-mechanism/index.json · license: https://xemstudio.com/files/hardware/face-spiral-rack-feed-mechanism/LICENSE.md

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

## Questions

**How does a spiral on a disc give a drill its feed?**

A spiral rib on the face of a disc engages a rack that slides radially over it: every turn of the disc moves the rack one pitch (3.14 mm) outward or inward — a slow, smooth feed from a continuously turning disc, the scroll-chuck principle used for the feed motion of drilling machines (the rack is on the drill's spindle sleeve).

## Fits with

- [Face spiral (scroll) disc, pitch 3.14 (module 1), r 20 → 46.39, Ø100 × 6](https://xemstudio.com/objects/face-spiral-disc-m1-r20-8-4turns-d100/)
- [Feed rack for a face spiral, module 1, 6 teeth, 19.05 × 8 × 7, curved teeth](https://xemstudio.com/objects/face-spiral-feed-rack-m1-6t-w8/)
- [Linear shafts Ø3 to Ø25 mm (h6), 100 to 1000 mm long](https://xemstudio.com/objects/linear-shafts-h6/)