# Quarter-turn belt between shafts at right angles (no guide pulleys)

> How does a quarter-turn belt drive work?

- Category: Mechanisms › Belt and friction drives
- Kind: Hardware
- Basis: Xem Studio design following Brown No. 4 (1868)
- Page: https://xemstudio.com/objects/quarter-turn-belt-drive-mechanism/ · JSON: https://xemstudio.com/api/geometry?object=quarter-turn-belt-drive-mechanism · Plain text: https://xemstudio.com/objects/quarter-turn-belt-drive-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

- A belt joins pulleys on shafts at right angles with no guides: each strand must run ONTO its pulley in that pulley's mid-plane (it may leave the other pulley at an angle). That fixes the layout: each pulley's mid-plane is tangent to the other pulley's belt circle, and the drive works in one direction only.
- Here two Ø40 × 12 plain pulleys, the second 60 mm along and 20 mm above the first; each strand twists a quarter turn. Both pulleys get 216.87° of wrap, more than an open belt — the extra contact Brown notes. Belt 12 × 1.5, inside length 271.4 mm.
- Brown's No. 4. Pulleys without flanges, faces exactly the belt's width, so the belt can leave at an angle.
- Parts (each has its own page): plain-flat-pulley-40x12, flat-belt-12x1-5-quarter-turn-40-40.
- Brown's movement No. 4 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

## Sizes

| parameter | value |
|---|---|
| pulleys | 2 × Ø40 × 12, plain |
| shaft angle | 90°, non-intersecting |
| offsets | 60 mm along, 20 mm up |
| wrap | 216.87° |
| belt | 12 × 1.5, 271.4 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. 4: figure, his text and an animation](https://507movements.com/mm_004.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/quarter-turn-belt-drive-mechanism/index.json · license: https://xemstudio.com/files/hardware/quarter-turn-belt-drive-mechanism/LICENSE.md

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

## Questions

**How does a quarter-turn belt drive work?**

A belt joins pulleys on shafts at right angles with no guides: each strand must run ONTO its pulley in that pulley's mid-plane (it may leave the other pulley at an angle). That fixes the layout: each pulley's mid-plane is tangent to the other pulley's belt circle, and the drive works in one direction only.

**Why does a quarter-turn belt only work one way?**

A belt must run onto a pulley in its mid-plane; reversed, each strand would run on at an angle and walk off the face.

## Fits with

- [Plain flat-belt pulley Ø40 × 12 face, Ø8 bore (no flanges)](https://xemstudio.com/objects/plain-flat-pulley-40x12/)
- [Quarter-turn flat belt 12 × 1.5 for two Ø40 pulleys at right angles (loop drawn on the pulleys)](https://xemstudio.com/objects/flat-belt-12x1-5-quarter-turn-40-40/)