The filament guide on my Ender snapped over the weekend. It is a small plastic arm that keeps the filament feeding cleanly into the extruder, and it had been creaking for a while before it finally gave up. The original is injection-moulded, which means I was never getting a spare without ordering one and waiting a week, paying more in postage than the part is worth.
Except the printer is, of course, a machine for making small plastic parts. There is something circular and faintly delightful about repairing a 3D printer with the 3D printer. I found a model on Thingiverse within minutes, somebody having long ago hit the same snapped arm and done the design work for all of us. Sliced it, printed it in PETG rather than PLA because this bit lives near the hot end and PLA goes soft if you so much as breathe on it warmly, and forty minutes later I had a replacement.
It fit on the first try, which never happens and made the whole afternoon. The old arm went in the spares box because I now print one before I need it, having learned that a printer mid-repair cannot print its own replacement part.
This is the part of the hobby I did not expect to enjoy as much as I do. Not the prints I plan, but the printer slowly becoming self-sufficient: fan ducts, cable clips, a better filament guide, a bracket to stop a thing wobbling. The machine maintains itself, and I just feed it filament and the occasional model. A repair that would have been a week and a delivery charge was an afternoon and a few pence of plastic. Hard to be cross about that.