# Planet-gear crank on a carrier round a fixed sun (variable traverse)

> How does a planet-gear crank vary a slider's stroke?

- Category: Mechanisms › Gears
- Kind: Hardware
- Basis: Xem Studio design following Brown No. 142 (1868)
- Page: https://xemstudio.com/objects/planetary-crank-variable-traverse-mechanism/ · JSON: https://xemstudio.com/api/geometry?object=planetary-crank-variable-traverse-mechanism · Plain text: https://xemstudio.com/objects/planetary-crank-variable-traverse-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 30-tooth sun gear is fixed; a carrier disc turns about it carrying a 30-tooth planet that rolls round the sun, making two turns per carrier turn. A crank pin on the planet (10 mm out) therefore traces a curve whose distance from the centre swings between 20 and 40 mm, and the rod from the pin to the slider gives a traverse that lengthens and shortens from stroke to stroke: Brown's variable-traverse motion for winding and tool feeds.
- Drawn at carrier angle 50° (planet turned 274°): pin at (20.5, 13.06), slider at x = 119.65 on the catalog slot guide, rod 100 mm.
- Brown's No. 142; module 1 throughout, centre distance 30 mm, the catalog 30 T crank gear and the catalog 30 T gear (sun) on a Ø10 shaft.
- Parts (each has its own page): spur-gears-module-1, crank-gear-m1-30t-pin-r10, planet-crank-carrier-disc-52-r30-boss10, four-bar-links, slide-block-12x6, slot-guide-plate-90, linear-shafts-h6, dowel-pins-metric.
- Brown's movement No. 142 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

## Sizes

| parameter | value |
|---|---|
| sun / planet | 30 T / 30 T, module 1 |
| carrier radius | 30 mm |
| crank pin | 10 mm on the planet |
| effective crank | 20 – 40 mm |
| rod | 100 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. 142: figure, his text and an animation](https://507movements.com/mm_142.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/planetary-crank-variable-traverse-mechanism/index.json · license: https://xemstudio.com/files/hardware/planetary-crank-variable-traverse-mechanism/LICENSE.md

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

## Questions

**How does a planet-gear crank vary a slider's stroke?**

A 30-tooth sun gear is fixed; a carrier disc turns about it carrying a 30-tooth planet that rolls round the sun, making two turns per carrier turn. A crank pin on the planet (10 mm out) therefore traces a curve whose distance from the centre swings between 20 and 40 mm, and the rod from the pin to the slider gives a traverse that lengthens and shortens from stroke to stroke: Brown's variable-traverse motion for winding and tool feeds.

## Fits with

- [Spur gears, module 1: 10 to 80 teeth (20° involute)](https://xemstudio.com/objects/spur-gears-module-1/)
- [Crank gear, module 1, 30 T with a Ø3 crank-pin hole at 10 mm](https://xemstudio.com/objects/crank-gear-m1-30t-pin-r10/)
- [Planet carrier disc Ø52 × 5 with a Ø10 × 13 planet boss at 30 mm](https://xemstudio.com/objects/planet-crank-carrier-disc-52-r30-boss10/)
- [Four-bar links: flat links with 20 to 100 mm hole centres](https://xemstudio.com/objects/four-bar-links/)
- [Slide block 12 × 6.2 mm for a 6.4 mm slot](https://xemstudio.com/objects/slide-block-12x6/)
- [Slot guide plate 90 × 30 × 5, 6.2 mm slot (74 long)](https://xemstudio.com/objects/slot-guide-plate-90/)
- [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/)