# Internal gear and pinion, 60 : 20 (3 : 1, same direction)

> Why does an internal gear turn the same way as its pinion?

- Category: Mechanisms › Gears
- Kind: Hardware
- Basis: Xem Studio design following Brown No. 34 (1868)
- Page: https://xemstudio.com/objects/internal-gear-and-pinion-mechanism/ · JSON: https://xemstudio.com/api/geometry?object=internal-gear-and-pinion-mechanism · Plain text: https://xemstudio.com/objects/internal-gear-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 meshing inside a ring gear: both turn the same way (an external pair reverses), the ratio is 60 : 20 = 3 : 1, and the centres are only m(N_ring − N_pinion)/2 = 20 mm apart — a compact reduction.
- More teeth are in contact than in an external pair of the same size (the concave ring wraps the pinion), so it carries more load, as Brown notes.
- Module 1, 20°; the ring's spaces are the exact involute tooth of a 60-tooth gear; no backlash drawn.
- Parts (each has its own page): internal-ring-gear-m1-60t, spur-gears-module-1.
- Brown's movement No. 34 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

## Sizes

| parameter | value |
|---|---|
| ring | 60 T internal, Ø80 |
| pinion | 20 T |
| ratio | 3 : 1, same direction |
| centre distance | 20 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. 34: figure, his text and an animation](https://507movements.com/mm_034.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/internal-gear-and-pinion-mechanism/index.json

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

## Questions

**Why does an internal gear turn the same way as its pinion?**

A pinion meshing inside a ring gear: both turn the same way (an external pair reverses), the ratio is 60 : 20 = 3 : 1, and the centres are only m(N_ring − N_pinion)/2 = 20 mm apart — a compact reduction.

## Fits with

- [Internal (ring) gear, module 1, 60 teeth, Ø80](https://xemstudio.com/objects/internal-ring-gear-m1-60t/)
- [Spur gears, module 1: 10 to 80 teeth (20° involute)](https://xemstudio.com/objects/spur-gears-module-1/)