# @stem_antics on Instagram

- **Type:** Video
- **Original URL:** https://www.instagram.com/p/Dakxc4egDvk
- **Gondola URL:** https://gondola.cc/posts/67635466-stem-antics-instagram
- **Thumbnail:** https://img.gondola.cc/tr:w-,h-,fo-auto/postThumbnails/fc33d65ae4.jpg
- **Posted:** 2026-07-09T13:56:12.000+00:00
- **Account Owner:** Stem Antics (@stem_antics) — https://gondola.cc/stem_antics

## Caption

Two parts machined deliberately the wrong size, then persuaded together with nothing but temperature. That is the quiet genius of the interference fit.

The idea is simple: make the shaft slightly larger than the hole it must enter. At room temperature they physically cannot slide together, so instead of forcing them and gouging both surfaces, you change their size with heat.

Thermal expansion follows a clean relationship:

ΔL = α · L · ΔT

where α is the coefficient of thermal expansion. Dunk the inner part in liquid nitrogen at -196°C and it contracts; heat the outer part in an oven or with induction and it grows. Steel sits around α ≈ 12 ×10⁻⁶ per K, aluminium nearer 23, so a modest temperature swing across a 100 mm diameter yields tens of microns of clearance, which is plenty for parts toleranced to a hair.

Slide them together while the gap exists, let them return to a common temperature, and something permanent happens. The metal tries to reoccupy its original dimensions, but neither part can. They lock in a state of continuous elastic strain, the outer component squeezing inward, the inner pushing outward. The contact pressure this generates, described by Lamé’s thick-walled cylinder equations, can run into hundreds of megapascals.

No adhesive. No weld. No keyway. Just two pieces of metal held by their own reluctance to be stretched.

This is how railway wheels grip their axles, how turbine discs hold blades against ferocious centrifugal loads, how bearing races seat and gears mount. Done right, the joint outlives the machine around it.

Cold and heat are not opposites here. They are the same tool, pointed in different directions.

#stemantics #engineering #mechanicalengineering #materialscience #manufacturing

## Stats

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## Tags

engineering, materialscience, manufacturing, mechanicalengineering, stemantics

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