I’m running into consistent overhang quality issues on a part that previously printed without any problems using the same printer and filament type. The underside of a supported overhang is now failing to form cleanly: it looks like the filament is not quite making solid contact with the tree support, causing the edge to drop slightly and leave trailing filament. This happens in the same part of the print in an identical fashion. This results in an uneven underside surface and reduced edge precision near the top of the part.
This is new behavior, this same geometry, orientation, and general setup worked reliably in the past.
Printer Model
Bambu Lab P1S
Using AMS
Filament
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Bambu PLA Basic and Bambu PLA Matte
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Tested with:
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older spools that previously printed successfully
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brand new spool
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dried filament and undried new filament
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Filament dried in food dehydrator at 120°F (~49°C) for 6 hours
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AMS humidity reads ~10%, confirmed with independent hygrometer
What I Have Already Ruled Out
At first I suspected filament moisture, but after drying and seeing the rest of the print behave normally (no popping, bubbling, or surface artifacts), I ruled this out (also after dehydrating my filament and then using filament that I had used a week ago that was not .
I also considered:
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Worn nozzle
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Issue occurred on:
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a semi used 0.4 mm nozzle (changed this out to the below)
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a fresh 0.2 mm nozzle
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a brand new 0.4 mm nozzle
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Loose belts
- Belts were tightened and tension is good
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Bed flatness or thermal issues
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Bed is not warped
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Temperatures read accurately during print (monitored in slicer during job)
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Set temperatures match actual readings
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Mechanical stability
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Printer is on a very sturdy table
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Has not moved since the time when prints were successful
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No unusual sounds during motion or extrusion
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Ambient conditions
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Room temperature is in the high 60s °F
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No drafts or airflow changes
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General maintenance
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Printer is ~3 years old
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Monthly maintenance performed consistently
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CAD File
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CAD file has not changed
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Verified geometry is identical to previously successful prints
Temperature & Slicer Adjustments
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Ran temperature tower
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Best results occurred at 200 °C but really this was splitting hairs (image attached)
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Historically I printed this part at ~220 °C without issue, which is why this change surprised me
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Updated filament profile to 200 °C after tower
Results were still inconsistent:
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sometimes slightly improved
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sometimes same failure on supported edge
Print Setup, Slicing & Speed Tests
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Changed part orientation
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Printed one part instead of two (normally prints as a pair and worked before)
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Tried different support types:
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Tree (normal)
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Tree (strong)
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Normal supports
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Changed slicing behavior of the overhang:
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changed underside layer direction
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changed bridge orientation where applicable
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Increased wall count
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Increased infill
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Applied speed modifiers to:
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slow down overhang regions
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reduce overall print speed in affected areas
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Tested lower temperatures specifically in overhang regions
All of these changes sometimes helped slightly, but results remained inconsistent, and I wouldn’t expect to need this level of tuning for a part that previously printed cleanly without any of these adjustments.
Key Question
Since this part and setup worked reliably in the past, I’m trying to understand:
What would cause supported overhang performance and light stringing to degrade suddenly on a P1S when filament, cooling, slicing strategies, mechanical stability, and hardware all appear normal?
Is the filament somehow still wet even after dehydrating it and the AMS and my manual meter showing as less than 13%? This all started when I put a new roll in the AMS and thought it was a bit wet / didn’t have a good seal.
Thanks in advance. This printer has been extremely reliable until now, so I’m trying to understand what changed and how to stabilize future prints and it’s sort of driving me bonkers.
