A gear bearing doesn't get assembled. It gets printed already inside itself — sun, planets and ring laid down in the same forty minutes, separated by a gap of two tenths of a millimetre, which is about as fine a distinction as a machine that squirts hot plastic can be asked to make.
It comes off the bed dead. The gap is theoretically there and practically full: teeth welded to neighbouring teeth by filaments thinner than a hair, a hundred small accidental joins. You can hold it up and turn it and nothing turns. If you didn't know what you were looking at, you'd file it under failed.
It didn't fail. It isn't broken. It's just not free yet.
There's exactly one move left, and it isn't a gentle one. You brace the outer ring in your palm, take the centre in your fingers, and twist harder than feels respectful toward a thing you just spent forty minutes making — until something gives. And something does give. A crack you feel before you hear, going round the whole circle at once.
Then it spins. And here's the part I keep turning over: it never needs that again. One bad moment, precisely aimed, and the thing runs smooth for years.
The clearance was designed in from the start. The machine put it there on purpose, knowing full well it would close. Nobody skipped a step. The gap was always real — it just had to be insisted on before it counted.