# Weighted belt tightener: pulley on a slide pulled by a hanging weight

> How does a weighted tightener keep a belt tight?

- Category: Mechanisms › Belt and friction drives
- Kind: Hardware
- Basis: Xem Studio design following Brown No. 23 (1868)
- Page: https://xemstudio.com/objects/weighted-belt-tightener-mechanism/ · JSON: https://xemstudio.com/api/geometry?object=weighted-belt-tightener-mechanism · Plain text: https://xemstudio.com/objects/weighted-belt-tightener-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 driven pulley turns on a slide that runs on guide rods; a weight hung from the slide pulls it away from the driver, so the belt stays at the same tension however it stretches.
- Belt tension ≈ half the weight's pull per strand: a 394.58 g steel weight gives about 1.94 N in each strand. Here Ø80 driver over a Ø40 pulley 150 mm below, 16 × 1.5 belt of 491.17 mm.
- Brown's No. 23 (hanging, weighted tightener on a sliding frame).
- Parts (each has its own page): flanged-flat-pulley-40, flanged-flat-pulley-80, flat-belt-16x1-5-pulleys-40-80-c150, tightener-slide-8mm-stub, hanging-weight-d40x40-lug, linear-shafts-h6, dowel-pins-metric.
- Brown's movement No. 23 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

## Sizes

| parameter | value |
|---|---|
| pulleys | Ø80 above Ø40, 150 mm |
| slide | 60 × 20 × 10 on 2 × Ø6 rods |
| weight | Ø40 × 40 (394.58 g steel) |
| belt | 16 × 1.5, 491.17 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. 23: figure, his text and an animation](https://507movements.com/mm_023.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/weighted-belt-tightener-mechanism/index.json · license: https://xemstudio.com/files/hardware/weighted-belt-tightener-mechanism/LICENSE.md

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

## Questions

**How does a weighted tightener keep a belt tight?**

The driven pulley turns on a slide that runs on guide rods; a weight hung from the slide pulls it away from the driver, so the belt stays at the same tension however it stretches.

## Fits with

- [Flanged flat-belt pulley Ø40, 16 mm face, Ø8 bore](https://xemstudio.com/objects/flanged-flat-pulley-40/)
- [Flanged flat-belt pulley Ø80, 16 mm face, Ø8 bore](https://xemstudio.com/objects/flanged-flat-pulley-80/)
- [Flat belt 16 × 1.5 for Ø40 and Ø80 pulleys at 150 mm (loop drawn on the pulleys)](https://xemstudio.com/objects/flat-belt-16x1-5-pulleys-40-80-c150/)
- [Tightener slide 60 × 20 × 10 with Ø8 stub axle, two Ø6 rod bores and a pin tab](https://xemstudio.com/objects/tightener-slide-8mm-stub/)
- [Hanging weight Ø40 × 40 with a pin lug (394.58 g in steel)](https://xemstudio.com/objects/hanging-weight-d40x40-lug/)
- [Linear shafts Ø3 to Ø25 mm (h6), 100 to 1000 mm long](https://xemstudio.com/objects/linear-shafts-h6/)
- [Dowel pins, 2–6 mm (ISO 2338 / DIN 6325)](https://xemstudio.com/objects/dowel-pins-metric/)