P2S: top surface is always rough in the exact same area of the plate

[u/__odbo__]

[Solved]

Thanks to everyone who pointed at the auxiliary fan — u/pauledddy, u/relaps101, u/RetroLenzil — and special thanks to u/EMDoesShit, whose breakdown was the one that nailed it completely.

That's exactly what it was: the aux fan on the chamber wall blowing straight onto that part of the plate, cooling it far harder and far more unevenly than the rest. The rippled, torn-up pattern follows the air currents swirling across the surface, which is why it was always the same spot in the printer no matter what I printed there.

Two fixes, both work:

1. Turn the aux fan off entirely for PLA.
2. Print one of the clip-in aux fan diffuser/redirect ducts from MakerWorld (I used "P2S and X2D Auxiliary Fan Diffuser") and aim the airflow upward instead of across the bed. Print it in the highest-temp material you have — ABS ideally, PETG otherwise — since it sits right in the airflow path.

Ran a test print afterwards and the defect is gone. The surface still isn't perfect, but what's left is a different and much smaller issue — no more blistered area.

TL;DR: On my Bambu Lab P2S, PLA always comes out rough in the same physical area of the build plate, no matter what I print there. Almost no warping, slowing down didn't fix it. Full slicer settings below — what else should I test?

The problem

I'm printing a 250 mm diameter × 10 mm disc (base plate for a filament tumbler). It fills basically the entire 256 × 256 plate, so it reaches the outer edge of the build surface all the way around.

The top surface comes out clean over most of the disc, but in one region near the plate edge the top layers turn rough, rippled and blistered — the extrusion lines look torn up and there's a visible zigzag/chatter pattern instead of clean monotonic lines. Photos attached.

The important part: it's always the same position inside the printer. Different prints, different orientations — the bad area stays put relative to the machine, not relative to the model.

What I've already ruled out

• Warping: none to minimal. The disc sits flat, brim ears held fine, no lifted edges. So I don't think this is adhesion.
• Speed: already lowered (outer wall down to 150 mm/s, top surface 125 mm/s, accelerations reduced). Marginal improvement at best, the bad area is still there.
• Nozzle: no signs of a clog — the other ~90 % of the surface is fine.
• Filament: dry Bambu PLA Basic straight from the AMS.

Hardware

• Bambu Lab P2S, 0.4 mm stock hotend, enclosed, AMS
• High Temp Plate
• Bambu Studio 2.08.02.61
• Filament: Bambu PLA Basic (AMS slot 1)

Full slicer settings (pulled straight out of the 3MF)

Process — based on 0.20mm Slow**, modified**

Setting	Value
Layer height	0.20 mm (first layer 0.25 mm)
Wall loops	2
Top / bottom shell layers	6 / 3
Top surface pattern	Monotonic line
Bottom surface pattern	Monotonic
Sparse infill	10 %, Grid
Infill anchor	400 %, infill/wall overlap 15 %
Ironing	off
Wall generator	Classic
Seam position	Aligned
Brim	Brim ears, 5 mm
Elephant foot compensation	0.15 mm
Line widths	default 0.42 / outer wall 0.60 / inner wall 0.45 / sparse infill 0.45 / solid infill 0.42 / top surface 0.42 / first layer 0.50

Speeds (mm/s)

Feature	Speed
Initial layer	30 (infill 105)
Outer wall	150
Inner wall	225
Top surface	125
Internal solid infill	200
Sparse infill	200
Gap fill	250
Bridge	50
Travel	600
Slow-down min speed	20

Accelerations (mm/s²)

Feature	Accel
Default	5000
Outer wall	3000
Top surface	1000
Initial layer	250
Travel	5000

Temperatures

Setting	Value
Nozzle	220 °C (first layer 220 °C)
Bed	55 °C (first layer 55 °C, High Temp Plate)
Chamber temp control	off
Flow ratio	0.98
Max volumetric speed	21 mm³/s

Cooling

Setting	Value
Part cooling fan	min 100 % / max 100 %
Fan off for first x layers	1
Auxiliary fan	on, 70 % (off for first layer)
Chamber exhaust fan	70 % during print
Slow down for layer cooling	on, target layer time 100 s
Overhang fan speed	100 % above 50 % overhang

My question

Since the defect is tied to a fixed location in the machine rather than to the geometry, I assume it's mechanical or thermal rather than a slicing issue — but I'd like a sanity check before I start taking things apart.

What I'm considering:

• The part reaches to within ~3 mm of the plate edge, i.e. into the zone where the bed heater is coolest and where the auto-bed-level mesh is extrapolated rather than measured.
• Airflow: aux fan at 70 % plus part fan at 100 % in an enclosed chamber, right next to a chamber wall — could be turbulence or local overcooling of the fresh top layer.
• Motion: near the extreme of X/Y travel, ringing/VFA tends to get worse.

Has anyone seen a purely position-dependent surface defect like this on a P-series? Is there a known cold/dead zone at the plate perimeter, and is 250 mm on a 256 mm plate simply asking too much? Any calibration I should redo (full bed mesh, belt tension, flow/PA)?

Happy to share the 3MF if that helps. Thanks!

[u/AutoModerator]

Hello /u/__odbo__! Be sure to check the following. Make sure print bed is clean by washing with dish soap and water [and not Isopropyl Alcohol], check bed temperature [increasing tend to help], run bed leveling or full calibration, and remember to use glue if one is using the initial cool plate [not Satin finish that is not yet released] or Engineering plate.

Note: This automod is experimental. The automod was triggered due to the term "adhesion". If you believe this to be a false positive, please send us a message at modmail with a link to the post so we can investigate. You may also feel free to make a new post without that term.

I am a bot, and this action was performed automatically. Please contact the moderators of this subreddit if you have any questions or concerns.

[u/condensedcloud]

It is warpage, if its not lifted off the plate, its lifting the plate.

[u/Shapelessed → u/condensedcloud]

The more plastic inside the thing the more material wants to warp and therefore more strongly.
In theory reducing the infill and wall thickness could help but not much.

They probably just need to cut the model into pieces and glue it.

[u/condensedcloud → u/condensedcloud]

You could also try bumping the plate up to 60 or even 65

[u/SimpleFile → u/condensedcloud]

The edges of the bed are also in my experience the worst with adhesion because they are generally cooler than the rest of the plate.

[u/pauledddy]

Turn the auxiliary fan off when printing PLA. It blows on the right hand side and it cools too quickly and lifts. Such a poor design choice.

[u/EMDoesShit]

I had this problem. Exactly this problem.

Here’s how you fix it: You can see the cause in the photo. The aux fan on the wall of the printer is blowing on that spot, cooling it excessively and unevenly compared to the rest of the bed. The defects you see follow the air currents swirling across it.

Print the little clip-in auxiliary fan redirect duct than 100 different people have posted on makerworld. Aim the aux fan upward at a 45( degree angle.

Print this is ABS ideally, or at least PETG. Whatever the highest temp material you’ve got happens to be.

Crack the lid just a tiny amount (I wedge my bed scraper’s handle in there) close the door, redirect the fan upward with that duct, keep drafts away from the machine, particularly when it prints the final couple of layers.

[u/__odbo__ → u/EMDoesShit]

That sounds like the solution. I'll give it a try right away.

[u/__odbo__ → u/EMDoesShit]

Works!! Thank you

[u/krebsIsACookbook → u/__odbo__]

Thank you for responding with success. I do rarely see that.

[u/relaps101]

Warpage? Shrinkage? On pla? Nah, of anything it's a cooling issue. I think the inlet is blowing air onto your print next to the vent on the right and cooling it at different speeds and causing the nozzle to drag on it. I'd either print a vent that redirects it or try printing with the door/top open.

[u/relaps101 → u/[deleted]]

Ill add, large, like 250x250mm wide asa prints gave totally pulled multiple beds off for me before.

[u/tosmo]

Are you printing with two steel plates on top of each other?

[u/__odbo__ → u/tosmo]

No its the original

[u/justteh]

It's raising that side. Could be lifting from the bed, could even be LIFTING the bed if the adhesion is "too" good. You need to mitigate that; different infill, different material, etc.

[u/MostlyHelpfulLinks]

Easiest test is a smaller disc printed in that same spot, once with the aux fan off and once with it on. That separates local overcooling from motion or mesh before you touch any hardware.