Still fairly new to the game here, so I can’t promise I’m not making any dumb mistakes..
I have an odd, ongoing issue with a model that I’ve printed successfully previously. For some reason, the support trees are randomly getting knocked down, typically before the first interface layer goes down (or maybe in the process of putting down the first layer?). I hadn’t been taking timelapse since I had printed this before, so I’ll have to review the timelapse of the latest print.
The portion of the print with the support is basically a thin wall cylinder with a small overhang (pic attached). The problem is seen with the supports inside and outside the ring. In this pic, you can see one of the outer supports has already been taken down..
Using 3 support layers with PLA./ PETG support filament (that has been dried).
Things I’ve done to troubleshoot so far
- cleaned the build plates
- swapped build plates (Smooth PEI and Textured PEI)
- Dried the filament (18 hours at 50C in a Creality dryer)
- Swapped out the desiccant in the AMS (hygrometer on the desiccant box shows 20%, Bambu is reporting 5% / A grade) - loaded with the freshly dried filament
- Swapped filament (PLA Matte and PLA Basic, problem happened with both, even after drying)
- Changed print speeds (I realize several of these are likely not relevant, just want to be through)
- Outer Wall 200→100
- Inner Wall 350 → 100
- Sparse Infill 430 → 150
- Top Surface 200 → 50
- Gap Infill 350 → 150
- Support 150 → 50
- Support Interface 80 → 50
- Tried multiple support types (Tree Organic, Slim, Hybrid)
- Decreased the branch distance 5 → 2
- Cleaned and lubed the Z-axis lead screws
- Ran the internal printer calibration immediately before starting a print.
- Autoleveling and flow calibration is always on for the prints.
What else should I be trying? Again, I’ve printed this model before and haven’t had these problems…
Trees get knocked down because of over-extrusion. Supports are delicate. If the nozzle deposits a blob on one, next time the nozzle comes around it’ll snag on the blob and take the support down. Blobs can form if you’re flowing too much plastic. Either your flow/PA isn’t tuned well enough, or the filament is still wet and needs more drying.
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Cool. Spent some time watching flow calibration tutorials. Good stuff. Thanks!
Three dumb questions -
- how would the filament still be wet after so long in the dryer? 18 hours seemed to be beyond what any site was recommending for pla.
- should I be checking any mechanical components since there seems to have been a change in the filament feed rate? I’ve used the same filament (different roll) successfully with this model . I bought this printer used with about 3k hours on it, so I wouldn’t be surprised if something needed attention.
- How often should I expect to recalibrate for the same type of filament? I wouldn’t expect enough variation between lots of the same filament… maybe that’s overly optimistic?
No dumb questions, just stupid answers. 
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When we “dry” our filament with heat, we’re not really drying it. The level of dryness is limited by the ambient humidity level. So there is no specific amount of drying time. And the effect is asymptotic. The closer the air in the dryer is to the ambient humidity level, the slower the filament’s humidity level drops. So it could easily take more than 18 hours. Except PLA doesn’t really absorb much and when it does it’s usually immediately obvious because it becomes brittle and easily breaks. But it’s not the PLA that’s knocking over the supports because the supports aren’t PLA. It’s the support filament you need to worry about. Unless you’re printing PETG and using PLA for supports?
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Filaments aren’t always that well controlled, diameter-wise. Even from one part of a roll to another. And many filament sellers buy from multiple sources and label it as their own brand (I believe BBL is in this category). So one batch to another, same label from same seller could even be from different manufacturers. If I’m really looking for the best quality print I can get, I calibrate each new roll before I use it. But if I’m in a bit of a hurry, I let the printer do flow and PA for itself. If you’ve never changed the extruder, 3K hours it’s probably getting due. They wear out.
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Optimistic.
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You clearly haven’t dealt with me… ha!
1- that makes sense. The dryers should be called heaters. Freakin’ false advertising… lol. Hygrometer has dropped to 10 with the filament in the ams, so I suspect it’s okay. That and the fact that I had the same problem with multiple filaments Oh - and I’m printing pla with pla supports and pla/petg for the interface layer.
2- also makes sense. The optimist in me wants to think that the printer can handle and adjust for small variations in diameter. But they are just consumer level machines, even if they’re pretty capable. I’ll run through the flow/pa calibrations before kicking off another print. Got any favorites for manual cal print samples? Sounds like they’re not built in… and I think I preordered an extruder when I was first going through the printer. Haven’t installed it yet, but I’ll get prepped in case the calibrations don’t fix it. But I’m definitely tempted to rebuild the model to eliminate supports
3-unsurprising… lol
Stil no luck. Did the flow calibrations (auto and manual) and still got the same results. I probably need to go over the hardware with a fine tooth comb to make sure nothing is damaged / broken / worn.
On the plus side, I rebuilt the model to break it down into pieces that didn’t need supports and it printed just fine. Prints without supports seem to print without problems, so I’ll go that route until I can take a day to tear into this thing.
Thanks for the feedback!
You mentioned using PETG as support interface and PLA as model filament. The pic also appears to show the tree knocked off at roughly the same layer an interface would be.
I suggest cranking your purge volume to the absolute maximum allowed by your slicer, both into and out of petg. Single nozzle multi material creates a contaminated nozzle of pla/petg mix and it prints worse than either. It must be VERY thoroughly purged, the more you can do, the better.
