# Rocking segment and band turning two pulleys to and fro

> How does a rocking segment drive two pulleys?

- Category: Mechanisms › Belt and friction drives
- Kind: Hardware
- Basis: Xem Studio design following Brown No. 6 (1868)
- Page: https://xemstudio.com/objects/segment-lever-band-pulleys-mechanism/ · JSON: https://xemstudio.com/api/geometry?object=segment-lever-band-pulleys-mechanism · Plain text: https://xemstudio.com/objects/segment-lever-band-pulleys-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 lever rocking on a pivot carries a circular segment; a band fixed to both ends of the segment passes round two pulleys below. Rocking the lever pulls the band one way, then the other, so both pulleys turn back and forth together, in the same direction.
- Pulley turn = segment turn × R_segment / R_pulley = 50/20 = 2.5: rocking the lever ±20° turns each Ø40 pulley ±50°. The segment's rim spans 198.83° so the band's 174.83° of wrap stays on it.
- Band 16 × 1.5, 510.14 mm; pulleys 70 mm apart, 110 mm below the pivot. Brown's No. 6.
- Parts (each has its own page): rocking-segment-lever-r50, flanged-flat-pulley-40, band-16x1-5-segment-r50-two-pulleys-40, linear-shafts-h6.
- Brown's movement No. 6 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

## Sizes

| parameter | value |
|---|---|
| segment radius | 50 mm |
| pulleys | 2 × Ø40 (catalog) |
| ratio | 2.5 : 1 |
| band | 16 × 1.5, 510.14 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. 6: figure, his text and an animation](https://507movements.com/mm_006.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/segment-lever-band-pulleys-mechanism/index.json · license: https://xemstudio.com/files/hardware/segment-lever-band-pulleys-mechanism/LICENSE.md

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

## Questions

**How does a rocking segment drive two pulleys?**

A lever rocking on a pivot carries a circular segment; a band fixed to both ends of the segment passes round two pulleys below. Rocking the lever pulls the band one way, then the other, so both pulleys turn back and forth together, in the same direction.

## Fits with

- [Rocking segment lever, R50 rim × 16, Ø8 pivot, 100 mm handle](https://xemstudio.com/objects/rocking-segment-lever-r50/)
- [Flanged flat-belt pulley Ø40, 16 mm face, Ø8 bore](https://xemstudio.com/objects/flanged-flat-pulley-40/)
- [Band 16 × 1.5 for the R50 segment and two Ø40 pulleys (drawn as a loop)](https://xemstudio.com/objects/band-16x1-5-segment-r50-two-pulleys-40/)
- [Linear shafts Ø3 to Ø25 mm (h6), 100 to 1000 mm long](https://xemstudio.com/objects/linear-shafts-h6/)