# Double-sided rack between two equal gears

> Why drive a rack from both sides?

- Category: Mechanisms › Gears
- Kind: Hardware
- Basis: Xem Studio design following Brown No. 115 (1868)
- Page: https://xemstudio.com/objects/double-rack-two-gears-mechanism/ · JSON: https://xemstudio.com/api/geometry?object=double-rack-two-gears-mechanism · Plain text: https://xemstudio.com/objects/double-rack-two-gears-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

- Two equal gears on fixed shafts 32 mm apart, turning in opposite directions, mesh with the two toothed edges of one rack: the rack is pushed with equal force and speed on both edges, so it runs straight with no side load on its guides.
- Module 1, 20-tooth gears (pitch Ø20) with their axes 10 mm outside each pitch line; one turn moves the rack 62.83 mm. Drawn with the rack one pitch (π mm) along.
- Brown's No. 115 (two equal toothed wheels driving a double rack).
- Parts (each has its own page): double-sided-rack-m1-100-pitch-12, spur-gears-module-1, dowel-pins-metric.
- Brown's movement No. 115 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

## Sizes

| parameter | value |
|---|---|
| gears | 2 × 20 T, module 1 |
| shaft centres | 32 mm |
| rack | 100 mm, teeth both sides |
| travel per turn | 62.83 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. 115: figure, his text and an animation](https://507movements.com/mm_115.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/double-rack-two-gears-mechanism/index.json · license: https://xemstudio.com/files/hardware/double-rack-two-gears-mechanism/LICENSE.md

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

## Questions

**Why drive a rack from both sides?**

Two equal gears on fixed shafts 32 mm apart, turning in opposite directions, mesh with the two toothed edges of one rack: the rack is pushed with equal force and speed on both edges, so it runs straight with no side load on its guides.

## Fits with

- [Double-sided gear rack, module 1, 100 mm, pitch lines 12 mm apart](https://xemstudio.com/objects/double-sided-rack-m1-100-pitch-12/)
- [Spur gears, module 1: 10 to 80 teeth (20° involute)](https://xemstudio.com/objects/spur-gears-module-1/)
- [Dowel pins, 2–6 mm (ISO 2338 / DIN 6325)](https://xemstudio.com/objects/dowel-pins-metric/)