# Double-helical (herringbone) gears, 20 : 30, helix 20°

> Why use double-helical (herringbone) gears?

- Category: Mechanisms › Gears
- Kind: Hardware
- Basis: Xem Studio design following Brown No. 41 (1868)
- Page: https://xemstudio.com/objects/double-helical-gears-mechanism/ · JSON: https://xemstudio.com/api/geometry?object=double-helical-gears-mechanism · Plain text: https://xemstudio.com/objects/double-helical-gears-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

- Each gear has two rows of oblique teeth of opposite hand meeting at the middle of the face: like single helical gears the teeth engage gradually and several are always in contact, but the two axial thrusts cancel, so no thrust bearing is needed.
- Here normal module 1.5, 20 and 30 teeth, helix 20° each way, 16 mm face; centre distance (r₁ + r₂) = 39.91 mm with the transverse module 1.6. Every transverse section is an exact involute spur mesh.
- Brown's No. 41 shows a second pair of oblique-toothed wheels; this page draws the double-helical form, the answer to the end thrust of No. 40.
- Parts (each has its own page): double-helical-gear-mn1-5-20t-beta20-bore6, double-helical-gear-mn1-5-30t-beta20-bore8, linear-shafts-h6.
- Brown's movement No. 41 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

## Sizes

| parameter | value |
|---|---|
| normal module | 1.5 |
| teeth | 20 / 30 |
| helix | 20°, both hands on each gear |
| face | 16 mm |
| centre distance | 39.91 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. 41: figure, his text and an animation](https://507movements.com/mm_041.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/double-helical-gears-mechanism/index.json · license: https://xemstudio.com/files/hardware/double-helical-gears-mechanism/LICENSE.md

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

## Questions

**Why use double-helical (herringbone) gears?**

Each gear has two rows of oblique teeth of opposite hand meeting at the middle of the face: like single helical gears the teeth engage gradually and several are always in contact, but the two axial thrusts cancel, so no thrust bearing is needed.

## Fits with

- [Double-helical (herringbone) gear, normal module 1.5, 20 teeth, helix 20° , face 16, Ø6 bore](https://xemstudio.com/objects/double-helical-gear-mn1-5-20t-beta20-bore6/)
- [Double-helical (herringbone) gear, normal module 1.5, 30 teeth, helix 20° , face 16, Ø8 bore](https://xemstudio.com/objects/double-helical-gear-mn1-5-30t-beta20-bore8/)
- [Linear shafts Ø3 to Ø25 mm (h6), 100 to 1000 mm long](https://xemstudio.com/objects/linear-shafts-h6/)