but it does not explain the weird burn mark of my initial failed print.

I guessing that when it was falling over, part it got taller. (Think of a 199 cm tall cabinet in a 200 cm room. It can’t fall over, it will hit the ceiling.)

As it got taller, the nozzle could dig in.

As the nozzle got embedded in the plastic, the heat would melt some plastic, and the dirt would stock to the warm molten sticky platic.

I get those when I print PETG too cold. Filament fails to stick to the print and cooks on the nozzle for a while, then gets wiped off eventually.

In addition to what others have said, this is definitely a failure of temperature control. Only some filaments will do more than turn liquid at temperatures that your print head should be seeing. (eg: PLA with hours of heat exposure)

If you never clean your print head (I always wire brush a nozzle before each print), it could just be buildup. Otherwise, I would take some time to check on what your printer thinks of a given temperature.

I’ve had to replace thermistors twice in the last 12+ years on my oldest printer (TAZ 6). Usually, it fails by being too cold and clogging. Though it has several times gotten too hot and produced similar results when it was going out or otherwise not thermally coupled well enough to the heating block. Rarely, it can be a connection issue between the controller and the thermistor.

Don’t be shocked if you have a few things to check and lock down before you solve the problem.

I have been printing more than a decade and have not seen this. But I suspect a clog? Then the filament burns inside and eventually comes out all chared? Or temperature control issues where you nozzle gets way too hot for short times? Just guessing here …

Edit: did some searching:

Burn marks on 3D prints usually appear as black or brown specks, streaks, or burnt blobs. They are primarily caused by melted plastic accumulating on the outside of the nozzle, gaps in your hotend causing filament to leak and cook, or a printing temperature that is simply too high.1. Clean the Outside of Your NozzleOften, small amounts of plastic cling to the hotend during printing. Over time, this filament cooks, oxidizes, and drops off onto your print.How to fix: Heat up your hotend to your printing temperature and carefully scrub the exterior of the nozzle and heat block with a small, brass wire brush.

1. Clean the Outside of Your NozzleOften, small amounts of plastic cling to the hotend during printing. Over time, this filament cooks, oxidizes, and drops off onto your print.How to fix: Heat up your hotend to your printing temperature and carefully scrub the exterior of the nozzle and heat block with a small, brass wire brush.

2. Check for Hotend Leaks (Loose Nozzle)If melted plastic is seeping out from the threads above the nozzle, it will slowly burn and periodically drip into your model.How to fix: Heat the hotend to at least 250°C. Hold the heater block with an adjustable wrench, and use a socket wrench to tighten the nozzle firmly. The goal is to make sure the nozzle sits completely flush against the heatbreak (or the PTFE tube on non-all-metal hotends).

3. Lower Your Printing Temperature

4. Remove Internal OxidizationIf you’ve recently switched from a dark-colored filament to a light-colored one (like white), residual burnt plastic from the dark filament can linger inside and randomly appear.How to fix: Manually extrude 10-20 cm of the new light filament through the hotend at a slightly higher temperature to push out all the old, oxidized residue.

the whole thing fell over…Do I need to make the model smaller, or is there something wrong with the print settings?

I haven’t done 3D printing for some time, despite following the community, but can you add a base, perhaps, that would make it more stable and is only attached at a few points and can be snipped off? There’s probably terminology for such a thing, but I’m afraid if there is, I don’t know it.

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