Bad top layer but only on sections near the back left of the bed

I print 90% of my objects with PETG, I use the same brand, and never have any issues. this is the first I have printed an object that is almost the full size of the bed. The object comes out great, except for the top surfaces on the very back-left corner of the bed. I have tried with print speed at 50% and 100%. I tried two brands of filament - my go-to Hatchbox brand does the best but still has issues, while Polymaker looks really awful. I haven’t played with settings yet because the whole print looks fantastic except for just the back-left section, and that is a reproducible issue. I can’t imagine the issue is settings if the print looks flawless everywhere but the back left corner.

Gyroid infull 15%, 4 top and bottom layers. The part is not lifting off the bed or warping.

I ran a calibration (via Orca slicer) and do an automated bed level with every print. This seems like an issue with the printer itself and not settings. What do you folks think?

This is Hatchbox brand. Not bad and hard to see the peeling/roughness, but note that it only occurs on this part of the object which is in the back left of the printer:

This is Polymaker brand. Much worse, but note that it only occurs on that same part of the object - back left corner.

May be it is time to review the cool settings and temperatures , i also use orca slicer for the same reasons with calibrated flow and calibrated K ( advanced Pressure ) note on the filament settings
Also from the print it looks the FLOW /K is not perfect. For PETG some times i increase the measured flow by 0.5% to 1% for better surface, K what i have measured , making sure that the bed is turned on for at least 10-15 minutes before i send the print( very cold here ) and let it cool down a bit before i open the door

Not sure if that helps but here is what i use note the chamber fan commands in the advanced section and the AUX fan (i change it some times between these values:

AUX/Chamber fan combination
Reduced Part fan
Increased Bed temperature and print temperature from the specs of my filament

EDIT: there was an error in the GCODE for the Chamber fan it was M106 P3 S150 not M106 P3 150

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Really hard to say what’s going on. Which maybe means there’s more than one thing going on here. I agree that issues with the left side of the print could be cooling related. But this looks almost like you’re under extruding. But the top of the extrusion should still be flat, the layer height is less than the extrusion diameter. And especially with these loops at the edges, the filament top is clearly nice and round. Like the nozzle is too high here. Which might also explain why the filament isn’t sticking to the underlying layer. Sticking requires the new layer to get squished in to the previous layer. If the printhead is too high that won’t happen (which is why supports with the same filament as the print are printed with a gap that is 1/2 of the nozzle diameter, so the extrusion will just rest on the previous layer). If the nozzle is too high, under extrusion will tend to cause the filament to get balled up. It doesn’t stay where it’s put, it’s under tension because the filament is flowing a little slower than the nozzle is moving, so it gets dragged along behind the nozzle. Every time the nozzle changes direction that string gets wrapped around it. Except, why would it only be higher for this top layer?

Given that the other filament works much better, the primary issue here has to be filament flow or PA. If it was mechanical it wouldn’t care which filament you were printing with. Unless the filament is only marginally tuned and a mechanical issue in this corner brings it out. You need to run the calibrations and also do a temperature tower for the “uglier” filament and see if those tweaks at least make it equivalent to the “prettier” filament. :slight_smile:

As for why that corner, assuming the chamber and aux fan isn’t running, I dunno. Hard for me to imagine it’s cooling related. Why would that corner be much hotter or cooler than the opposite corner, for example? Front of the build plate, with air gaps around the door, yes. But not the back. And if it was the build plate, I’d expect it to mess with the first layer not the last.

Things to try:

If you rotate the model 90º on the build plate, does the issue stay in that corner or follow the model rotation? If so, there’s something funny with the model (I doubt this is it).

If you scale the model down to 1/4 size and print it so it’s still in the same left/rear position, is the issue still there? (this will change the outcome if it’s cooling related)

Tram the build plate. And then run a straight edge across the back edge and left edge and see if that left rear corner is low. The auto-level doesn’t measure everywhere, if the build plate height changes unevenly between the sample points, the printer doesn’t see it. (I’m not sure how I can see this being it)

Dry the “uglier” filament a lot longer and see if that makes a difference.



@djnibler I confirm that there is something happening in the left back corner did a quick test (2h+ print )
NO BRIM 10mmx150mmx150mm with two wholes,
the same settings as you 15% , gyroid infill , the overlap is 15%… with the settings i sent , just the speed left it to the max for good quality PETG which is 140-155mm/S i usually print at 100mm
Bed temp 80C first layer and 70C rest , i did reduce it from 80 at some point for some reason and forgot to bump it but not so relevant as everywhere else is fine
I usually wait 15 minutes , to warm up the chamber and equalize it but this time just print it

  • The top surface has issues in the corner not as bad as yours but still bad
  • This corner edge detaches warp tiny from the bed, even with out brim should not happen - have not seen warp with PETG for a while and is a strange one very localized
  • considering that i have no issues on Prusa without enclosure , this is strange
    -looks like problematic areas is 30-40mm

Here are the photos and if i have luck identifying the actual cause or solution will share
But it looks like some thermal issue in the corner , and i have not really ever printed right to the edge with PETG , but should have noticed it with ASA , no chamber fan no AUX fan for ASA

  • for the next test i will try to bump the plate temp to 80 as usual and wait to warm up the chamber and reduce a bit the chamber fan to 60%, or may try ASA first right at the corner to check if not air flow
  • If some one has thermocouple would be nice to measure right at the corner and in the middle to see the difference while the plate is 10-15 mm from the print head and bed temp 70C , aux fan set to 10% and chamber fan set to 70-80%

    This is the bottom
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Before i go to bed as this problem was a bit of a puzzle a small update

@RocketSled i already tried most of this
i am using just a normal test plate and reducing the size with each print

  • ASA the problem is still there - as a refernce

  • 90 degree does not help and the defect does not follow the rotation

  • scaling down definitely helps but not sure if not related to some other changes to a level that disappears but with cooling changes as well

  • TODO check if there is not a low spot - possible but in two printers ?

@djnibler the uglier filament as Rocket suggested is just not dried or not well calibrated(flow/K) it is obvious from one of the photos flow looks like under extruding and looks like wet , but that is different problem and makes it more prominent . But dry and calibrate the ugly one
@djnibler Important the settings i gave you made a mistake in the advance the fan must be M106 P3 S150

interesting that the corner only does not get adhesion and micro warp is happening and the top surface looks like either extrusion problem or localized temperature cooling problem

also i see very minor surface inconsistence usually would not see it , but magnifying now it starts from the rear corner hole and the second hole and continues to the opposite corner
Tried ASA with scaled down version , increased print temperature added brim increased the overlap with the walls and the problem almost disappear the micro warping is gone in this corner only , and improved the corner surface but

I have 3 theories at the moment

  • some thermal problem from in this area either plate and just happens that the wholes in the model and the type of infill increase the problem
  • under extrusion in this area - may be the PTFE tube or filament has a big resistance ( unlikely)
  • Rockets suggestion for uneven plate

So far done 4 prints 130mm PETG problem exists , 100mm ASA problem reduced , 60mm ASA with brim and other changes problem almost gone , 60mm PETG no AUX fan and Chamber fan only for the last 4 layers 60% infill direction changed from 45 to 90 degrees.

Solved for smaller PETG
PETG reduced size AUX fan off , Chamber fan was off and on only for the last top 4 Layers 60% and infill rotated at 90degrees

ASA the two tests with the brim is 60mm with out the brim is 100mm

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Thank you both for all the help and replies.

Since you suggested it, I used a laser thermometer to check bed temp. Center is hottest, and back-left is second hottest. Remaining three corners are all cooler by about 5-10F.

I don’t have an aux part cooling fan on my setup. I do have an enclosure, but for PETG I run it with the lid off - so the sides are just in place. I do that only to help prevent drafts.

I am not having any issues with bed adhesion, even in the back left area. This leads me to think it’s not bed temp and it’s not a warped or out of level bed. Bed isn’t warped that I can see, when I lay a ruler across it.

But I agree with the suggestion that the z-offset seems to be wrong - yet only for the top surface and only for the portion of the top surface that is in the very back. But just considering issues in the back-left corner, I don’t understand how the base layer could be fine, the infill fine, but the top surface there is not fine. I haven’t changed the calibration for top surface specifically, and if there were a problem with it, why would it only occur in the back left?

Vladimir, you said," Solved for smaller PETG
PETG reduced size AUX fan off , Chamber fan was off and on only for the last top 4 Layers 60% and infill rotated at 90degrees"

Are you saying you turned off your aux part cooling fan and your chamber fan - but you turned on one or both of those fans for the top layers and that solved the issue? I’m not aware of any settings in Orca slicer where you can change fan speeds for top layers only.

Solved for me: dam a lot of work

@djnibler That makes sense now and i was able to solve it for me with cooling profile and a bit of tweeek in the settings , Just checked the last night(morning ) and is solved at least on my setup
here are all the changes i did from the original settings i sent you , not sure about your print speed but do not think it makes difference as i printed at max for PETG speed 140 and one model was at 70 no much difference
I also had bed adhesion problem in the corner !! now is gone
But please check if the bed level is really flat in the corners as Rcoket sugested bed leveling is not done right to the end

@RocketSled thanks for the hint with scaling

The new printed model 145mm by 145mm which is the bigger than the first tested model

  • Closed door
  • Lid ON
    - Infill direction - set to 90degrees( for the gyroid) - that changes the top layer to be parallel of the plate - noticed that under some circumstance between the wholes have ghosting like on the top shell when printed diagonally and that is more prominent around the rear left corner or start from there
    - 5mm Brim outer
  • moved it only 5mm from the side - this was accident but still in the area where was happening before
    - Print Bed 80C/80C - changed from 80/70
    - well warmed chamber before start of the print - to make sure that tbedplate is evenly heated
    - AUX Fan OFF
    - Chamber FAN - 60% - for you this may vary a bit here is not too warm

For my setup i think 70% Chamber fan will be a bit better , but not sure and marked the one sections which i think make the most difference

If i have to be really picky:
I see tiny ghosts like lines from the holes in direction of the print but that is with magnifying and probably is caused by slightly imperfection of K factor( i was getting 3 values and was not sure which one was the best on my filament - but as it is next to invisible will not warry and usually if i wont prefect top layer i put 6 top layers instead of 4

Hope that helps

@djnibler i sent a support ticket to see if Bambu can come up with ideas and solve my timelaps broken videos

The latest settings worked for me , for the rear corner, but in the middle of the plate complex print is not ideal especially with overhangs , too hot , so i reverted partial AUX fan (10%)for my other prints not sure if the corner is a problem as i have not tested it again . My prints usually do not use that corner

Support asked for log from the printer , and i provided one but i have done quite a few prints since and now busy with something else to start a new test print ,

If you can do one log from the printer may help ( personally i do not believe will show anything) but is is good to satisfy the support to keep on investigating. Or just export it next time you have the same problem and share it here

Or just open a new ticket and add the file and the print files and the forum link
and you can mention that is related to Ticket No: US230905543001
Curious how good is Bambu support really