# Geneva stop (Maltese cross stop-work): finger wheel limited to four turns

> How does a Geneva stop limit the number of turns?

- Category: Mechanisms › Intermittent motion
- Kind: Hardware
- Basis: Xem Studio design following Brown No. 212 (1868)
- Page: https://xemstudio.com/objects/geneva-stop-winding-stop-mechanism/ · JSON: https://xemstudio.com/api/geometry?object=geneva-stop-winding-stop-mechanism · Plain text: https://xemstudio.com/objects/geneva-stop-winding-stop-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: centres; stays the same: star, turns allowed, engagement; step to the nearest standard size (and redraw the hole or pocket it fits): pin.
- 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.
- A finger wheel with one pin indexes a five-position Maltese cross one position per turn, the locking disc holding the cross still in between (a Geneva drive). One of the five positions is not a slot but a convex tooth: when the pin comes round to it the tooth will not let it in, and the finger wheel is stopped — after four turns in one direction (and four back). Brown: used in Swiss watches to limit the winding; the convex curved portion of the star is the stop.
- Standard Geneva proportions on 40 mm centres: pin radius a·sin 36° = 23.51, star tip radius a·cos 36° = 32.36, so the pin enters and leaves each slot along the slot (no shock); Ø4 pin in 4 mm slots, locking disc Ø41.02 cut back by the star's exact sweep. Checked at ten wheel angles through an indexing and at the last slot before the stop: no overlap beyond contact; with the stop tooth in place of a slot the pin collides 6° past the entry angle (75.4 mm³), which is the stop.
- Drawn with the pin entering the second slot (-20° before the line of centres), the stop tooth three positions on.
- Parts (each has its own page): geneva-stop-finger-wheel-r23-5-pin4, geneva-stop-star-5-positions-4-slots-r32-4, linear-shafts-h6.
- Brown's movement No. 212 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

## Sizes

| parameter | value |
|---|---|
| centres | 40 mm |
| star | 5 positions: 4 slots + 1 stop tooth |
| pin | Ø4 at r 23.51 |
| turns allowed | 4 |
| engagement | 108° of the wheel's turn per index |

## 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. 212: figure, his text and an animation](https://507movements.com/mm_212.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/geneva-stop-winding-stop-mechanism/index.json · license: https://xemstudio.com/files/hardware/geneva-stop-winding-stop-mechanism/LICENSE.md

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

## Questions

**How does a Geneva stop limit the number of turns?**

A finger wheel with one pin indexes a five-position Maltese cross one position per turn, the locking disc holding the cross still in between (a Geneva drive). One of the five positions is not a slot but a convex tooth: when the pin comes round to it the tooth will not let it in, and the finger wheel is stopped — after four turns in one direction (and four back). Brown: used in Swiss watches to limit the winding; the convex curved portion of the star is the stop.

**What is the difference between a Geneva drive and a Geneva stop?**

The same wheel and cross; the stop has one slot replaced by a convex tooth, so the cross cannot go round and the driver is limited to n − 1 turns.

## Fits with

- [Geneva stop finger wheel: Ø4 pin at r 23.51, Ø41.02 locking disc, Ø6 bore](https://xemstudio.com/objects/geneva-stop-finger-wheel-r23-5-pin4/)
- [Geneva stop star: 5 positions, 4 slots and one convex stop tooth, Ø64.72, Ø5 bore](https://xemstudio.com/objects/geneva-stop-star-5-positions-4-slots-r32-4/)
- [Linear shafts Ø3 to Ø25 mm (h6), 100 to 1000 mm long](https://xemstudio.com/objects/linear-shafts-h6/)