The extruder arm on my Ender cracked. Specifically the spring-loaded lever that holds the filament against the drive gear, a known weak point on the stock printer, made of the sort of brittle plastic that exists to be replaced. The obvious fix was to buy an aluminium one. The funnier fix, and the one I went with, was to print a replacement on the very printer that needed it.
There is a pleasing recursion to a machine making its own spare parts, and it is genuinely how a lot of these printers stay alive. The Thingiverse and Printables ecosystem is full of upgrades and repairs designed to be printed by the thing they repair: cable chains, fan ducts, belt tensioners, the lot.
the part still has to last
The catch is that the broken part broke because it was under constant load, and PLA, the easy default, creeps under sustained stress and goes soft if the hotend warms it. So this is one of the few cases where material choice actually matters rather than being a preference.
I printed the replacement arm in PETG:
- higher temperature tolerance, which matters when it sits next to a 200°C hotend
- better layer adhesion and a bit of flex before it snaps, rather than the glassy shatter PLA gives you
- enough toughness to take the spring tension without creeping over a few weeks
Settings that worked for me:
material: PETG
nozzle temp: 240C
bed temp: 80C
layer height: 0.2mm
walls: 4 perimeters
infill: 60% gyroid
print speed: 30mm/s
The high wall count and chunky infill matter more than usual here. This is a structural part, not a desk ornament, and the load goes through the body of it. I would rather it be slow and solid than fast and back on my bench in a fortnight.
printing the repair before you need it
The annoyance, of course, is that you need the printer working to print the part that fixes the printer. Mine still extruded, just badly, with the lever held by a zip tie as a field repair to get one clean print out of it. If yours is fully down, this is where a friend with a working machine, or a spare printed in advance, earns its keep.
Which is the actual lesson. Now that it works again, I have printed a second arm and a couple of the other usual-suspect parts and put them in a drawer. The best time to print the spare is while the printer is healthy. A 20p coil of PETG and an hour of print time is a cheap insurance policy against an evening of swearing at a zip tie.