# Pinion between two racks (opposite motion, pump drive)

> How does one pinion move two racks in opposite directions?

- Category: Mechanisms › Gears
- Kind: Hardware
- Basis: Xem Studio design following Brown No. 127 (1868)
- Page: https://xemstudio.com/objects/opposed-racks-and-pinion-mechanism/ · JSON: https://xemstudio.com/api/geometry?object=opposed-racks-and-pinion-mechanism · Plain text: https://xemstudio.com/objects/opposed-racks-and-pinion-mechanism/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/)

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

## Notes

- A pinion between two parallel racks drives them in opposite directions at the same speed: rocking the lever on the pinion's shaft raises one rack (and its pump piston) while lowering the other.
- Racks are two full-depth module 1, 120 mm racks with their pitch lines 20 mm apart (one pitch diameter of the 20-tooth pinion); each moves π·m·N = 62.83 mm per pinion turn.
- Brown's No. 127 (air pump: lever and spur gear driving two racks on the piston rods).
- Parts (each has its own page): gear-rack-m1-120-full-depth, spur-gears-module-1, hand-lever-60-bore6, dowel-pins-metric.
- Brown's movement No. 127 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

## Sizes

| parameter | value |
|---|---|
| pinion | 20 T, module 1 |
| racks | 2 × 120 mm, pitch lines 20 mm apart |
| travel | 62.83 mm per turn, opposite ways |
| lever | 60 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. 127: figure, his text and an animation](https://507movements.com/mm_127.html) — web — Publisher's page; dimensions are facts

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

Index: https://xemstudio.com/files/hardware/opposed-racks-and-pinion-mechanism/index.json

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

## Questions

**How does one pinion move two racks in opposite directions?**

A pinion between two parallel racks drives them in opposite directions at the same speed: rocking the lever on the pinion's shaft raises one rack (and its pump piston) while lowering the other.

## Fits with

- [Gear rack, module 1, 120 mm, full-depth 20° teeth](https://xemstudio.com/objects/gear-rack-m1-120-full-depth/)
- [Spur gears, module 1: 10 to 80 teeth (20° involute)](https://xemstudio.com/objects/spur-gears-module-1/)
- [Hand lever, 60 mm, Ø6 hub bore](https://xemstudio.com/objects/hand-lever-60-bore6/)
- [Dowel pins, 2–6 mm (ISO 2338 / DIN 6325)](https://xemstudio.com/objects/dowel-pins-metric/)