# Crane strap brake: steel strap round a drum, tightened by a lever

> How does a strap (band) brake work?

- Category: Mechanisms › Belt and friction drives
- Kind: Hardware
- Basis: Xem Studio design following Brown No. 242 (1868)
- Page: https://xemstudio.com/objects/crane-strap-brake-mechanism/ · JSON: https://xemstudio.com/api/geometry?object=crane-strap-brake-mechanism · Plain text: https://xemstudio.com/objects/crane-strap-brake-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 steel strap wraps most of the way round a drum on the hoist shaft. One end is anchored on the lever's fulcrum, the other on the lever close to it, so pressing the handle pulls the strap tight round the drum. Its grip grows along the wrap: the tension ratio between the ends is e^(μθ), 3.31 for μ = 0.3 over the 228.78° drawn, and the brake torque is (T1 − T2) × R.
- Drum Ø60 × 20, strap 20 × 1.5 touching the drum over 228.78° with both legs tangent, pins 24 mm apart 48 mm below the axis, lever handle 142 mm from the fulcrum. Drawn snug, lever level.
- Brown's No. 242 (strap brake used on cranes).
- Parts (each has its own page): brake-drum-60x20-bore10, brake-strap-20x1-5-drum60-pins24, strap-brake-lever-130-pins24, dowel-pins-metric, linear-shafts-h6.
- Brown's movement No. 242 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

## Sizes

| parameter | value |
|---|---|
| drum | Ø60 |
| wrap | 228.78° |
| tension ratio (μ 0.3) | 3.31 |
| lever ratio | ≈ 6 : 1 |

## 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. 242: figure, his text and an animation](https://507movements.com/mm_242.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/crane-strap-brake-mechanism/index.json · license: https://xemstudio.com/files/hardware/crane-strap-brake-mechanism/LICENSE.md

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

## Questions

**How does a strap (band) brake work?**

A steel strap wraps most of the way round a drum on the hoist shaft. One end is anchored on the lever's fulcrum, the other on the lever close to it, so pressing the handle pulls the strap tight round the drum. Its grip grows along the wrap: the tension ratio between the ends is e^(μθ), 3.31 for μ = 0.3 over the 228.78° drawn, and the brake torque is (T1 − T2) × R.

## Fits with

- [Brake drum Ø60 × 20, Ø10 bore](https://xemstudio.com/objects/brake-drum-60x20-bore10/)
- [Brake strap 20 × 1.5 wrapped 228.78° round a Ø60 drum, eyes on Ø4 pins 24 mm apart](https://xemstudio.com/objects/brake-strap-20x1-5-drum60-pins24/)
- [Strap-brake lever: fulcrum and strap pins Ø4 24 mm apart, handle to 142 mm](https://xemstudio.com/objects/strap-brake-lever-130-pins24/)
- [Dowel pins, 2–6 mm (ISO 2338 / DIN 6325)](https://xemstudio.com/objects/dowel-pins-metric/)
- [Linear shafts Ø3 to Ø25 mm (h6), 100 to 1000 mm long](https://xemstudio.com/objects/linear-shafts-h6/)