Show HN: I engineered a 2mm micro-bearing D20 ring that free-spin for 20 seconds

Summary

Over the past few months I’ve been experimenting with how small a functional bearing-based mechanism can get while still feeling smooth, durable, and useful. This project started from a simple question: How thin can a real, free-spinning bearing be while still handling continuous rotation?Most “spinner rings” you see online cheat by simulating rotation — there’s no real bearing, just loose tolerance metal sliding on metal. True micro-bearing rotation needs precision, tight tolerances, and high surface finish, which is difficult when everything needs to be wearable on a finger.So I tried to push it in the opposite direction and ended up making this:A 2mm-thick stainless steel ring with an internal micro-bearing track and 20 steel balls that free-spin for 20+ seconds with a single flick.Mechanical details: • CNC machined inner race with ~0.01mm tolerance • 20 micro steel balls loaded through a lateral channel • Outer ring pressed onto the bearing shell • No plastic, no bushings, no lubricant • Built to withstand everyday wearing forces (compression, torsion, micro-impacts) • PVD variant for color durability • Outer surface can be marked 1–20, turning it into a tiny randomizerOriginally the goal was purely mechanical — to see if a bearing this thin could be made. But it ended up being surprisingly functional for solo tabletop RPG use: when you need a quick random result but don’t have table space, or when dice are too loud (playing in bed, on a commute, etc.). The ring spins silently and lands pointing at a single number.This wasn’t meant to replace dice; it just became a neat side effect of the engineering challenge.Why I’m posting hereHN tends to appreciate: • micro-manufacturing • tolerances • machining challenges • precision mechanical design • unusual “why does this work?” projectsI’d love to hear feedback on: • improving durability • minimizing friction losses • alternative ball materials • raceway finishing • any tricks for increasing spin time without adding th...