# @stem_antics on Instagram

- **Type:** Video
- **Original URL:** https://www.instagram.com/p/DdfqCryRZM-
- **Gondola URL:** https://gondola.cc/posts/70577827-stem-antics-instagram
- **Thumbnail:** https://img.gondola.cc/tr:w-,h-,fo-auto/postThumbnails/77c670b8de.jpg
- **Posted:** 2026-09-20T03:50:12.000+00:00
- **Account Owner:** Stem Antics (@stem_antics) — https://gondola.cc/stem_antics

## Caption

A spur gear is a series of small collisions. Every tooth arrives across its full face width at once, and that line contact is where gearbox noise, pitting and shock loading are born.

Angling the teeth solved it. In a helical gear the contact line starts at one corner of the flank and sweeps diagonally across it, so load is transferred progressively instead of slammed on. More tooth pairs share the mesh and the transmission error that drives noise falls sharply.

The penalty is thrust. A helix pushes sideways as it drives, producing axial force equal to the tangential force multiplied by the tangent of the helix angle. At 30 degrees that is more than half the driving load pushing along the shaft: large thrust bearings, parasitic losses and a ceiling on usable helix angle.

The herringbone answer is to mirror the helix about the mid face. Two opposed helical halves on one blank, and the axial components cancel internally as an equal and opposite pair inside the gear body.

- Thrust never reaches the bearings, so radial bearings alone carry the shaft
- Helix angles of 30 to 45 degrees become practical, raising the overlap ratio
- Higher total contact ratio spreads torque across more teeth, cutting root bending stress
- The mesh self centres axially, so one shaft is left to float and both halves share load

Manufacturing lagged the geometry. Hobs and shaving cutters need somewhere to run out, so early double helical gears carried a central relief groove that wasted face width. The Sykes gear shaper, built in England in the 1910s, drove opposed cutters toward the centre and generated a true continuous apex.

André Citroën bought the rights to a chevron tooth cutting process in Poland in 1900 and built Société des Engrenages Citroën around it. The double chevron on every car he later made is a gear tooth.

The cleanest way to kill a force is to generate its mirror image.

#stemantics #mechanicalengineering #gears #manufacturing #engineeringdesign

## Stats

- **Views:** 10,153
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## Tags

engineeringdesign, manufacturing, mechanicalengineering, gears, stemantics

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