# Fast and loose pulleys with bevel gears: start, stop or reverse an upright shaft

> How do fast and loose pulleys reverse a shaft through bevel gears?

- Category: Mechanisms › Gears
- Kind: Hardware
- Basis: Xem Studio design following Brown No. 7 (1868)
- Page: https://xemstudio.com/objects/bevel-reversing-gear-fast-loose-pulleys-mechanism/ · JSON: https://xemstudio.com/api/geometry?object=bevel-reversing-gear-fast-loose-pulleys-mechanism · Plain text: https://xemstudio.com/objects/bevel-reversing-gear-fast-loose-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

- Resize: multiply every length by one factor k and the motion stays identical: angles, ratios, timing and the formulas below do not change, because a mechanism's motion depends only on the ratios of its lengths. Here, scales with k: pulleys, driving pulley; stays the same: gears; step to the nearest standard size (and redraw the hole or pocket it fits): upright shaft.
- Resize: Gears scale by the module m (pitch Ø = m·z, centre distance = m·(z₁ + z₂)/2): keep the tooth counts so the ratio stays, and choose a standard module (0.5, 0.8, 1, 1.25, 1.5, 2, 2.5, 3).
- Resize: fit clearances stay in mm (a slide fit is the same gap at any size); keep every printed wall and pin at least two nozzle widths; mass grows with k³ but part strength only with k², so at k = 2 parts are about 8× heavier and 4× stronger: check pins and thin links when scaling up.
- Two mitre gears face each other on a cross shaft and both mesh with a third on the upright shaft. One (A) is keyed to the cross shaft, which carries the fast pulley; the other (B) runs loose with its own pulley; between them is a loose idler pulley.
- Belt on the fast pulley: the shaft turns gear A and the upright shaft turns one way. Belt on B's pulley: gear B, on the other side of the upright gear, turns it the other way. Belt on the idler: it stops. The belt is shifted sideways along the wide driving pulley. Brown draws the two bevels on a shaft and a hollow shaft one inside the other; here B simply runs loose on the one shaft.
- Three module 2, 24-tooth spherical-involute mitre gears (cone distance 33.94 mm), Ø40 × 16 pulleys on a Ø5 shaft; the three gears were checked in mesh at six angles. Brown's No. 7.
- Parts (each has its own page): mitre-gear-m2-24t-bore5, plain-flat-pulley-40x16-bore5, plain-flat-pulley-40x52, flat-belt-16x1-5-pulleys-40-40-c130, linear-shafts-h6.
- Brown's movement No. 7 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

## Sizes

| parameter | value |
|---|---|
| gears | 3 × mitre, module 2, 24 T |
| pulleys | 3 × Ø40 × 16 (fast, idle, loose) |
| driving pulley | Ø40 × 52, 130 mm above |
| upright shaft | same speed, either direction |

## 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. 7: figure, his text and an animation](https://507movements.com/mm_007.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/bevel-reversing-gear-fast-loose-pulleys-mechanism/index.json · license: https://xemstudio.com/files/hardware/bevel-reversing-gear-fast-loose-pulleys-mechanism/LICENSE.md

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

## Questions

**How do fast and loose pulleys reverse a shaft through bevel gears?**

Two mitre gears face each other on a cross shaft and both mesh with a third on the upright shaft. One (A) is keyed to the cross shaft, which carries the fast pulley; the other (B) runs loose with its own pulley; between them is a loose idler pulley.

## Fits with

- [Mitre (bevel) gear, module 2, 24 teeth, Ø5 bore, spherical involute (spline flanks)](https://xemstudio.com/objects/mitre-gear-m2-24t-bore5/)
- [Plain flat-belt pulley Ø40 × 16 face, Ø5 bore (no flanges)](https://xemstudio.com/objects/plain-flat-pulley-40x16-bore5/)
- [Plain flat-belt pulley Ø40 × 52 face, Ø8 bore (no flanges)](https://xemstudio.com/objects/plain-flat-pulley-40x52/)
- [Flat belt 16 × 1.5 for two Ø40 pulleys at 130 mm (loop drawn)](https://xemstudio.com/objects/flat-belt-16x1-5-pulleys-40-40-c130/)
- [Linear shafts Ø3 to Ø25 mm (h6), 100 to 1000 mm long](https://xemstudio.com/objects/linear-shafts-h6/)