Here’s the thing: when printing on my Bambu A1 Mini (whether PLA or PETG), the protruding parts curl upward. This causes the nozzle to catch on them and break off thin parts, sometimes tearing the prints and generally ruining the look. I’ve already tried reducing the print speed, adjusting both the bed and nozzle temperatures (both on the low and high side). I’ve tried different filaments. Even the ones that are perfectly dry still curl up. The bending itself begins somewhere around 1 cm from the table. Everything sticks to the table itself well and there is no warping. Has anyone encountered this and how did you solve it?
It’s an extreme overhang. There’s no material in the previous layer for the plastic to bond to, so it will curl to some extent, no matter what settings you use. This is inherent to FFF 3D printing.
Use supports or reorient your model to not have extreme overhangs.
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Classic curling.
- Really dry filament
- Draft free, warmish print environment (PLA likes 30-35°C but that may be tricky with an A-series)
That is usually enough for PLA.
PETG is a different beast as it has very different cool down behavior leading to warping and curling much more quickly.
However, slowing down and/or reducing layer height can help further. Just don’t be timid. Think in halves and quarters of the problematic speeds/layer heights.
Supports can also help to even out the curl inducing cooling. Note the support interfaces can themselves suffer from curling though, shifting the problem.
& 
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I still don’t think that’s the issue. I increased the z-hop and ran an FDM test, and it’s running quite well now, nothing has fallen off anywhere. BUT the bending hasn’t gone away, it just doesn’t catch on the nose anymore and doesn’t ruin the model. And while it was printing, I got the feeling that the bends were happening because the filament was either hardening too quickly or too slowly, and when the nozzle retracted, it was pulling on it instead of laying down enough new filament. It seemed like underextrusion, although there were no visible problems elsewhere. Only in the overhanging areas. And it didn’t matter what the angle was—the bends were happening even on models with a very small angle.
Is everyone really using supports for a temp tower?
I would try rotating the model to see if the AUX fan is affecting it first.
The model’s orientation doesn’t affect it at all. Yesterday I printed a box whose edges had hexagonal holes on all sides—and every other hexagon suffered from bending 
From a purely material science perspective AND considering this context, thermal expansion and contraction of plastic wants to happen regardless of how fast the change in temperature occurs. You either get movement, or you get internal stresses.
At the moment of extrusion, you’re laying down hot plastic that is at it’s most expanded, and only a small part of the material’s volume is anchored to something below it.
As it cools, the material shrinks, beginning with the outer material and ending with the core material. The material that is unsupported and on the very top will always contract as it cools, and that means curling upward. It won’t curl downward because the material is contracting, not expanding, and it won’t stay put because thermal expansion and contraction is non-negotiable. In a well designed part without overhangs, you can reduce the thermal effects, but even then, you are getting some movement, and also internal stresses - which can later be annealed out.
Physics isn’t optional.
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So, based on your answer, I have a physics major, but the rest of the typing team decided to take a vacation because there’s no such problem? I get it, thanks.
If you watch that print get laid down irl as it is happening you will see, likely, that entire lip be molten and quiver as the new line is put down and likely curl back up, still molten
More total time between layers can help that sort of thing, or cooling tuning in general. (Part fan. Aux fan. Chambe temp. Slow for overhang. Nozzle temp. Tons and tons of controls.)
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Warping and its little cousin curling are well understood FDM failure modes which became more prominent with the higher speeds the Bambu’s introduced. The underlying principles were clearly and succintly described by @CarbonForge .
Of course, there are further details that have drastic consequences on the material behavior. Drafts, filament moisture, thick, wide & fast lines are just some of the factors in warping.
You can find plenty of posts here on warping, what is causing it and how to prevent it.
Here’s just one:
Of course, it could also be something different or maybe even new.
But please share the relevant information.
Pic’s, key parameters used (specific material and pre-print drying conditions, nozzle size and layer height, environmental temp, speeds, cooling settings, changes made to defaults (z-hop was changed, how about wipe-on-retract?, what else?), which “FDM test” (there are thousands! Hardly any adhere to any kind of standard though …).
As a hint, temp towers give visual indications of the effects of specific settings such as retract, z-hop, wipe-on-retract, bridging parameters, drooping and curling at different temperatures with all further key settings (in particular flow, flow dynamics, part fan, aux-fan, env. temp) fixed (i.e. dialed in).
It is very misleading if there may be moisture in the filament though.
To properly start at the beginning:
How do you know? How long did you dry which filament at which temp?
Just in case:
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I recently got two rolls of PETG, CC3D brand in Silver. Perfectly sealed packaging, still held vacuum. BOTH were WET! When the flow line (the thin line before a print starts) has bubbles in it, you know it’s wet. When doing a cold pull afterwards and the extruded filament is rough textured instead of smooth, you know it’s wet.
IOW never assume a brand new sealed roll is dry. Took 20 hours in the dryer before I could even calibrate it. OTOH I have had rolls of PLA that were submerged in loose bags when my basement flooded that printed perfectly without drying.
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