# @stem_antics on Instagram

- **Type:** Video
- **Original URL:** https://www.instagram.com/p/DdRTZ6mS4WX
- **Gondola URL:** https://gondola.cc/posts/70577851-stem-antics-instagram
- **Thumbnail:** https://img.gondola.cc/tr:w-,h-,fo-auto/postThumbnails/ee147cc1e4.jpg
- **Posted:** 2026-09-14T14:03:12.000+00:00
- **Account Owner:** Stem Antics (@stem_antics) — https://gondola.cc/stem_antics

## Caption

A ball nose end mill cuts with a hemisphere, and that single geometric choice rewrites every number on the setup sheet. 

The fix is geometry, not feed rate.

	•	Effective diameter governs everything. For an axial depth ap on a ball of radius R, D_eff = 2 x sqrt(2Rap - ap^2). At 0.2 mm depth a 10 mm ball engages only 2.8 mm of diameter, so real surface speed is under a third of the nominal figure.
	•	Tilting the spindle 10 to 15 degrees on a five axis machine shifts the contact patch clean off the dead centre, restores cutting speed and loads a stronger section of the flute.
	•	Stepover sets finish. Residual scallops between adjacent passes stand at h = ae^2 / 8R, so halving the stepover quarters the cusp height. A 0.2 mm stepover with a 10 mm ball leaves a one micron ridge, which is why finishing paths crawl across a surface in fractions of a millimetre.

The tooling is a century of metallurgy. Karl Schroeter patented cemented tungsten carbide at Osram in 1923, commercialised by Krupp as Widia in 1926. Modern AlTiN coatings build an aluminium oxide skin in the cut and hold hardness past 800 degrees Celsius, which lets a 2 mm ball finish hardened H13 at 55 HRC.

The toolpath lineage is older still. John Parsons and Frank Stulen, with the MIT Servomechanisms Laboratory, computed helicopter rotor contours point by point on punched cards and demonstrated numerical control in 1952. Every machined curved surface descends from that arithmetic.

A flat end mill removes material. A ball nose end mill defines a surface.

#stemantics #cncmachining #manufacturing #engineering #machining

## Stats

- **Views:** 7,456
- **Likes:** 29
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- **Comments:** 2

## Tags

machining, engineering, cncmachining, manufacturing, stemantics

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