# Two speeds from two belts on fast and loose pulleys

> How do fast and loose pulleys give two speeds?

- Category: Mechanisms › Belt and friction drives
- Kind: Hardware
- Basis: Xem Studio design following Brown No. 60 (1868)
- Page: https://xemstudio.com/objects/fast-and-loose-pulleys-two-speed-mechanism/ · JSON: https://xemstudio.com/api/geometry?object=fast-and-loose-pulleys-two-speed-mechanism · Plain text: https://xemstudio.com/objects/fast-and-loose-pulleys-two-speed-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

- The upper shaft carries a wide Ø80 and a wide Ø40 pulley; each drives its own belt. Below, each belt can run on a fast pulley (keyed to the shaft) or on a loose one beside it (free to turn). With belt 1 on its fast Ø40 the lower shaft runs at 2 × upper speed; shift belt 1 to its loose pulley and belt 2 onto its fast Ø80 and it runs at 0.5 ×.
- Drawn in the fast (2 : 1) setting: belt 1 on the fast Ø40, belt 2 idling on the loose Ø80. Both belts are the same length, 471.36 mm (Ø40 + Ø80 at 140 mm). Pulleys plain (no flanges) so the belts can be shifted; upper faces 34 mm wide for both positions.
- Brown's No. 60. Only one belt may be on a fast pulley at a time.
- Parts (each has its own page): plain-flat-pulley-80x34, plain-flat-pulley-40x34, plain-flat-pulley-40x16, plain-flat-pulley-80x16, flat-belt-16x1-5-pulleys-40-80-c140-open, linear-shafts-h6.
- Brown's movement No. 60 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

## Sizes

| parameter | value |
|---|---|
| upper pulleys | Ø80 × 34 and Ø40 × 34 (fast) |
| lower pulleys | Ø40 fast + loose, Ø80 loose + fast, × 16 |
| speeds | 2 : 1 and 1 : 2 |
| belts | 2 × 16 × 1.5, 471.36 mm |
| shafts | Ø8, 140 mm apart |

## 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. 60: figure, his text and an animation](https://507movements.com/mm_060.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/fast-and-loose-pulleys-two-speed-mechanism/index.json · license: https://xemstudio.com/files/hardware/fast-and-loose-pulleys-two-speed-mechanism/LICENSE.md

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

## Questions

**How do fast and loose pulleys give two speeds?**

The upper shaft carries a wide Ø80 and a wide Ø40 pulley; each drives its own belt. Below, each belt can run on a fast pulley (keyed to the shaft) or on a loose one beside it (free to turn). With belt 1 on its fast Ø40 the lower shaft runs at 2 × upper speed; shift belt 1 to its loose pulley and belt 2 onto its fast Ø80 and it runs at 0.5 ×.

## Fits with

- [Plain flat-belt pulley Ø80 × 34 face, Ø8 bore (no flanges)](https://xemstudio.com/objects/plain-flat-pulley-80x34/)
- [Plain flat-belt pulley Ø40 × 34 face, Ø8 bore (no flanges)](https://xemstudio.com/objects/plain-flat-pulley-40x34/)
- [Plain flat-belt pulley Ø40 × 16 face, Ø8 bore (no flanges)](https://xemstudio.com/objects/plain-flat-pulley-40x16/)
- [Plain flat-belt pulley Ø80 × 16 face, Ø8 bore (no flanges)](https://xemstudio.com/objects/plain-flat-pulley-80x16/)
- [Flat belt 16 × 1.5 for Ø40 and Ø80 plain pulleys at 140 mm (loop drawn)](https://xemstudio.com/objects/flat-belt-16x1-5-pulleys-40-80-c140-open/)
- [Linear shafts Ø3 to Ø25 mm (h6), 100 to 1000 mm long](https://xemstudio.com/objects/linear-shafts-h6/)