A shutdown drill for your desk. Armed, it just sits there — three rods standing on a latch, doing nothing. Press the mushroom and all three drop at once with a clack you feel through the desk, and the only way back is to earn it: forty-three ratchet clicks on the crank, through a 3.5:1 gear train, until they seat again. Sixteen printed parts, zero fasteners, and not one of them decorative.

It started with a reactor trip. The seed was one line in a morning news feed: St Lucie Unit 1 shut down, three control rods dropped into the core. Every printed reactor out there is scenery, a shape to look at. Nobody had built the one part of a reactor that is actually a machine — the drop. This is for people who want a desk object with a cycle: arm it, fire it, earn the reset.

Press the button, and all three drop. Three rods stand cocked on a spring-loaded latch, their tops proud of the red deck. Press the pale grey plunger and the wedge on its stem drives the latch bar 0.20 inches back, freeing all three at once: they fall about half an inch until their tops sit level with the deck, and their chisel feet punch a bistable rocker over so the plinth window snaps from GREEN to SCRAM.