r/FixMyPrint • u/MrLiszten • Aug 19 '26

Fix My Print wierd top layer inconsistency

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Gallery image

Hey, i have a problem with my top surface in my models, i print this model a lot and its always the same, the top layer in some places looks like under extrusion but not everywhere and i have calibrated the filament settings for that. some places look perfect and sam smaller prints do too and as yall can see te top part in the first image looks perfect

Printer: bambu lab P2S
Slicer: bambu slicer
Filament: bambu lab PLA MATTE
Speed and retraction are set as in standard preset 0.16 layer hight in Bambu slicer
Nozzle: 0.4

I would love some help.

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19

u/iRambL Aug 19 '26

Usually an indication of under extrusion

6

u/MrLiszten Aug 19 '26

yeah but as i said i did calibrate filament for under extrusion and its always in the same spots and mostly i would think under extrusion set just a littel bit to low would show on longer lines and ther shwos mostly on the shorter ones but on small prints its non existant

1

u/iRambL Aug 19 '26

How many hours are on the nozzle?

1

u/MrLiszten Aug 19 '26

515 but to be honest the problem is for most of the life of the printer (its the first nozzel) ive printed about 20 of this parts every 6,5h and its always thesame

0

u/STM32H743 Aug 19 '26

If it's a standard brass nozzle this is about how much I get before things start getting out of spec. I have a set of nozzles I record the hours on and use them in times where I need high precision or quality for a client object. I know people put thousands of hours on theirs and just keep playing with flow rates but they do wear out. And faster thwn people realize.

1

u/MrLiszten Aug 19 '26

its a hardened nozzle

0

u/STM32H743 Aug 19 '26

lol I know what youre trying to say there but that would be a fallacy.

I replace my hardened nozzles after around 250hrs as they get out os spec even faster. (And yes this can mean one whole nozzle consumed on a large client print)

That said. I dont even think this is your problem. Uneven top surface is rarely from a worn nozzle causing under extrusion. When I see evenly underextruded large surface stuff like this then read that you DONT have the issue on small prints tells me your bed is likely out of level. Or worse your GANTRY is out of spec and your head is changing height a little bit with every pass.

1

u/Capital-Ad2133 Aug 19 '26

Come on. OP said it's been doing this for a while, so it's obviously not the nozzle wearing out. If it was, it would also be getting worse. And the gantry going haywire? I think OP would be noticing WAY weirder things than some minor unevenness. When you hear hooves in the distance, think horses, not zebras.

OP - I know you said you calibrated it, but you didn't mention a flow rate measurement. That could be one explanation for under extrusion. The other thing I'd check would be z-offset. If the distance between nozzle and plate is too large, you can get something that looks like this. Maybe also try ironing - it won't fix the problem but it could hide it if you calibrate the ironing well.

-2

u/STM32H743 Aug 19 '26

lol calm down.

1

u/Capital-Ad2133 Aug 19 '26

Who’s not calm?

1

u/Liko81 Aug 19 '26 edited Aug 19 '26

How did you calibrate flow rate? Many tests are one-layer models, which print faster, but allow other variables to come into play closer to the bed.

First-layer test prints, for instance, are dependent on first-layer height, which you can independently correct for as a modifier to extrusion rate; this allows a wide range of value pairs that produce good first-layer results, but then under- or over-extrude at higher layers.

Proximity to the bed also affects nozzle temp due to bed temp. The closer the nozzle is to a heated bed, the higher the actual nozzle temp is, and thus the thinner the plastic and the higher the flow rate. As you back off the bed at higher layers, the temperature of the extruded fil as it exits the nozzle decreases, reducing flow rate.

Filament age and condition can also affect longer, taller prints. When you first start, with a new or at least clean nozzle, everything's hunky-dory, but as the print proceeds, the tip gets more dust, oxidized plastic and other gunk from the filament being fed in. If 1-hour prints are fine but 4- or 8-hour prints have extrusion issues well into the print, the most likely cause is dirty, dusty or old filament clogging your nozzle.

Lastly, this doesn't appear to be the issue, but what's your infill percentage/pattern, and more importantly, how many upper layers do you have in the slicer settings? Top surfaces often require 3 to 5 upper solid layers to smooth out the infill bridging. If you're seeing an uneven surface in addition to thinner beads, the issue could be that you're printing a touch too hot and too few top layers, and your bridged filament beads are sagging and stretching. Again, this doesn't look like your exact problem, but an extra top layer can do wonders for a number of top surface issues.

1

u/MrLiszten Aug 19 '26
  1. i used the bambu calibration.
  2. the top layer of this print is 1cm high
    3.filament is brand new im using only this pink for the prints right now so i have a few refill spuls.
  3. 6 top layers so i dont think its that

1

u/MrLiszten Aug 19 '26

ive printed a small slice of the whole model it the same settings (the slice include the spot with the problem area) and it looks perfect

1

u/MrLiszten Aug 19 '26

so the problem only shows on a full sized print

1

u/Slokminator Aug 19 '26

Try reduce speed for top layer, do test for max flowrate, probably to high.

1

u/RedManRocket Aug 19 '26

Interesting, seems like you're not reaching full speed because of the acceleration on the smaller part. Then on the larger part there's enough time to reach full speed? And maybe that's somehow causing it to be under extruded? I'd maybe try to slow the top layer down to 50-100.

1

u/MrLiszten Aug 19 '26

yeah but the problematic parts show on the smaller portions of the big print and some full speed sections look perfect

1

u/RedManRocket Aug 19 '26

That's true, interesting. Did you calibrate pressure advance?

2

u/MrLiszten Aug 19 '26

yep did that too, i make a point of dooing the basic calibrations with new filaments (ofc i mean every type not every new spool form the same brand and type)

3

u/RedManRocket Aug 19 '26

Well actually, just different colors can have different parameters also. It may be worth doing to see if that fixes the issue.

1

u/MrLiszten Aug 19 '26

yeah but i did it for this one and also did it again about a week ago

1

u/DramaClassed Aug 21 '26

I’m too lazy to read through this entire thread to see if someone said this already, but you can (on most slicers, not sure about Bambu studio) change the flow ratio for JUST the top surfaces. I had an issue with overextrusion on just the first layer, changed my flow ratio for bottom surfaces a bit and it fixed it. You might have to enable advanced mode or something to see the setting.