# @stem_antics on Instagram

- **Type:** Video
- **Original URL:** https://www.instagram.com/p/DbdtCtmAnIO
- **Gondola URL:** https://gondola.cc/posts/68532552-stem-antics-instagram
- **Thumbnail:** https://img.gondola.cc/tr:w-,h-,fo-auto/postThumbnails/de73525628.jpg
- **Posted:** 2026-07-31T16:35:43.000+00:00
- **Account Owner:** Stem Antics (@stem_antics) — https://gondola.cc/stem_antics

## Caption

A keycap legend that never fades is not printed onto the plastic. It is grown inside it.

Double shot injection moulding builds a single keycap from two separate injections, in two separate cavities, without the part ever leaving the machine.

The sequence:
- Shot one fills the legend cavity, forming the character as a solid slug of resin
- The index plate rotates 180 degrees, carrying the part on its core
- Shot two injects the outer shell around it, filling every void the first shot left
- The two melts fuse at the interface under heat and injection pressure

The result is a character with genuine depth. The legend is not a coating sitting on the surface. It runs down through the wall of the cap. Abrasion attacks both plastics at the same rate, so the character stays legible long after the surface texture has polished smooth under a fingertip.

The hard part is the counters. The enclosed void inside an O, an A or a Q would float free, with no path connecting it to the rest of the legend. Double shot tooling solves this by webbing those islands to the main character below the visible surface, buried inside the cap wall. Older keyboards showed the crude version of the same fix as visible ligatures cutting through each letter.

Registration is the second constraint. Both cavities must align to within tens of microns, across thousands of cycles, through the thermal expansion of a steel tool running hot. Any drift appears as a halo of the wrong colour around every character.

Material choice tightens it again. ABS is amorphous and shrinks roughly half a percent. PBT is semi crystalline, shrinks around three times as much, and distorts as it crystallises. Two PBT shots pulling against each other will lift a cap out of flat. That is why double shot PBT arrived decades after double shot ABS.

Printing sits on a surface. Moulding becomes one.

#stemantics #injectionmoulding #manufacturing #materialsscience #polymers

## Stats

- **Views:** 38,420
- **Likes:** 219
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- **Comments:** 4

## Tags

polymers, injectionmoulding, materialsscience, manufacturing, stemantics

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