# @stem_antics on Instagram

- **Type:** Video
- **Original URL:** https://www.instagram.com/p/Db1wNGvAPZs
- **Gondola URL:** https://gondola.cc/posts/69054413-stem-antics-instagram
- **Thumbnail:** https://img.gondola.cc/tr:w-,h-,fo-auto/postThumbnails/726df1c3f6.jpg
- **Posted:** 2026-08-10T00:43:50.000+00:00
- **Account Owner:** Stem Antics (@stem_antics) — https://gondola.cc/stem_antics

## Caption

That cutter is a gear, and it is cutting a gear.

Gear shaping is a generating process. The tool is a hardened pinion with relieved flanks and ground rake, and it reciprocates along the axis of the blank while both cutter and workpiece rotate in a fixed timed ratio. Nothing on the machine holds the shape of a tooth. The involute profile appears as the envelope of hundreds of overlapping straight cutting positions, exactly the surface two meshing gears would roll against each other.

The plate on this machine reads ВНУТРЕННИЙ, meaning internal, which is the entire point. Hobbing is faster for open external gears, but a hob is a worm and needs run out clearance to sweep past the face. Inside a ring gear there is no such room. A shaper only needs the length of the stroke plus a shallow undercut groove, which is why internal ring gears in planetary drives, wind turbine boxes and automatic transmissions are almost always shaped.

The details that make it work:

- The cutter withdraws a few tenths of a millimetre on the return stroke so the flanks do not rub and burnish the freshly cut surface
- Depth is taken in radial passes, the cutter plunging in while rolling, then finishing at full depth for profile accuracy
- Each cutter loses diameter as it is resharpened on the rake face, so the design uses a tapered relief that keeps the profile correct through the whole life of the tool
- Chips leave as tight curls because every stroke is an interrupted cut, which is also why the sound is so rhythmic

Edwin Fellows patented the method in Springfield, Vermont in the 1890s after concluding that the only tool guaranteed to produce a correct gear tooth was another gear tooth. That logic has not been improved upon in over a century.

A gear is the only honest master pattern for another gear.

#stemantics #gearshaping #manufacturingengineering #machining #mechanicaldesign

## Stats

- **Views:** 16,061
- **Likes:** 200
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- **Comments:** 3

## Tags

stemantics, gearshaping, manufacturingengineering, mechanicaldesign, machining

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