The filament guide on the back of my printer snapped over the weekend. A small printed bracket, the kind that came with the kit, that routes the filament off the spool and into the extruder at a sensible angle. Brittle PLA, a year of UV from the window, and one careless tug while changing a roll. Snap.
There is a particular satisfaction, and a particular absurdity, in the fix. I went to the project's repo, found the STL for that exact part, and printed a replacement on the printer that was missing it. It managed fine without the guide for the twenty minutes it took, because the broken part was a convenience, not load-bearing. So the machine printed the thing it needed to keep printing things. The snake ate exactly enough of its own tail to be useful.
I did make one change rather than printing the original verbatim. The snapped part failed because the layers split along the direction of stress, which is the classic 3D-printing weakness: prints are strong across layers and weak between them. So I reoriented it on the bed so the force runs along the layer lines instead of across them, and bumped the walls from three perimeters to five. Same geometry, printed sideways, noticeably tougher. PETG would have been the proper answer for something near the hot end and in the sun, but I had PLA loaded and impatience winning.
This is the bit of the hobby I find quietly lovely. A normal appliance breaks and you order a part or bin the lot. This one breaks and the repair is a forty-minute print and a hex key. It is not magic, it is just that the bill of materials is a folder of STLs, and a spare is whatever you can be bothered to slice. The printer fixed itself, with a little supervision, and went back to work.