Nozzle and hot-end care

The nozzle is the one part of your printer that touches molten plastic on every single print, and it's a consumable — a small brass orifice that slowly changes shape as it works. That matters more than it sounds, because the nozzle bore is the master reference for every dimension your machine produces. The width of every bead, the thickness of every wall, the real size of every hole and clearance — all of it is set, at the last moment, by the hole the plastic squeezes through. Keep that hole clean and the right size and your calibrated numbers hold. Let it drift and everything drifts with it.

Wear: the bore that widens under you

Brass is soft, and abrasive filaments are merciless. Carbon-fibre, glass-fibre and glow-in-the-dark filaments are loaded with hard particles that sand the inside of a brass nozzle like a file — a heavily filled spool can visibly widen a 0.4 mm brass bore in a matter of a few hundred grams to a kilo, depending on the abrasive load. Even plain PLA erodes it slowly over many spools.

A worn nozzle doesn't fail dramatically; it lays down a wider, less precise bead. And it isn't only the bore widening: with carbon-fibre filament the tip itself also erodes and flattens, so you lose both the right diameter and the sharp edge the tip uses to define the bead — both degrade bead accuracy. And because the bead is wider, walls thicken and holes close in — so a fit you calibrated months ago quietly creeps toward tight, then toward seized, with no single print to blame. This is the slow drift from When your tolerances drift, and the nozzle is its most common cause. If your fits have all gone subtly wrong at once and nothing else changed, the bore that made them has probably grown.

The defence is matching the nozzle to the material. For abrasives, a hardened-steel or ruby-tipped nozzle resists the wear that eats brass — at the cost of slightly worse heat conduction. It's the single upgrade that keeps your dimensions stable if you print filled materials at all, and it's covered in Nozzles: diameter, wear and hardened steel.

Clogs: when the bore narrows instead

The opposite failure is a partial clog — carbonised plastic or a leftover speck narrowing the bore from the inside. The bead comes out thin, inconsistent, or under-extruded, and the same dimensional logic runs in reverse: walls thin, gaps open, and fits loosen. A fully blocked nozzle just stops extruding.

The gentle fix is a cold pull. Heat the hot end, push a length of filament (nylon or a cleaning filament works well) through, let it cool to the point where it's solid but still grips, then pull it out sharply — the plug of debris comes with it, moulded to the inside of the nozzle. Repeat until the tip you pull out is clean. It's the least invasive way to clear a fouled hot end without taking it apart.

Changing a nozzle — and why you re-check after

Swapping a nozzle is routine: heat the hot end so the plastic inside is soft, hold the heater block steady, and change the nozzle warm so it seats against the break without leaving a gap for plastic to ooze into. A clean, properly seated nozzle is half of a clean hot end; the other half is keeping stray plastic off the outside of the tip, where it chars and drops blobs into your print.

But here's the part that closes the loop with the rest of this section: a new nozzle is a new machine, dimensionally. Even the same nominal 0.4 mm, from the same brand, can lay down a slightly different bead — a hair of variation in the bore, a different heat profile, a fresh sharp edge. Every fit number you calibrated was measured through the old nozzle. Swap it and those numbers are provisional until you prove them again.

Keep the hole clean, the right size, and re-measured after every change, and the nozzle stops being a source of drift. The other half of dimensional honesty lives below the nozzle — in the plate the part sits on and the motion that places it — which is Bed and motion upkeep.