Curling on edges, issues on overhang


I´ve got a problem printing a part with an overhang of ~40° and sharp edges (60°).

In the edges, the filament curls up, which builds up more and more with every layer. In two out of three corners the print comes out in a decent quality anyways but there ist always one edge where it looks crappy. I tried to move the seam to another edge and also set it to random but that didn´t change anything. Sometimes I can also print the part with no issues.

Does anybody know what could be the problem here?

I use bambu pla with the factory settings. The top lid is open, I tried front door open and close but that didn´t change anything. I also tried lowering the speed at overhangs but that also didn´t help.

In the CAD-File the I added fillets to the edges, so they are not pointy.

Thanks in advance!

You need more part cooling.

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Quite impressive ski jump.

Did you dry and calibrate your filament (yet)? That would explain some of the other features in the pic’s.

Next, the ski jump usually comes from material shrinkage during cool down. A cooling layer deposited on an already cooled layer will shrink, pulling up the material it is deposited on.
So you will want to reduce the temperature differences between the layers by keeping the environment warm (closed door and lid although this slightly increases the risk of heat creep).
You will also want to limit the amount of heat deposited per layer so you should A) go (much) slower on overhangs and B) consider adaptive layer height.

With PLA, that should resolve the bulk of this problem. I have found that in particular going slower makes the time to first succesful print much faster. :joy:

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Thanks for your quick answers, although they confuse me a bit.

If I understand correctly, both answers say the opposite of each others?

@heapstar says it needs more cooling - the previous layers are even cooler than the new layer.

@EnoTheThracian says less cooling so there is less temperature difference between existing layers an new layers.

For calibration, I only used the automatic flow calibration and I didn´t dry the pla filament so far. Since I unpacked it it was only sitting in the AMS with silica.

Meanwhile I tried to print the part in a different orientation with the following result:

The second picture shows the opposite side of the first one. I´m not quite sure which side was oriented to the fan but I could imagine that it´s either a cooling issue like @heapstar pointed out or a too much cooling on one side which would fit to @EnoTheThracian s guess and the side oriented to the fan turned ot better/worse than the other side.

I will now try to calibrate the filament, then try again once with door and lid open and once with everything closed and see what happens and remember which side was oriented to the fan.

I will let you know.


The lower layers only can only be pulled up if not hardened (cooled) enough. This effect is adding up layer by layer. The layertime of such small parts is often too short to cool the part enough even with massive cooling. A convenient trick is to print a bunch of these parts (if required) to increase layertime without slowing down the printer. Or print small parts alongside another (bigger) part.

Another reason for curling is adding too much material (and with this temperature also) at the corners. Your part is looking over extruded so there might be sometimes a problem with pressure advance and/or flow. The Bambu auto calibration has about 10 % precision says the manual, which is sometimes not enough for delicate parts.

Here you can see how long the lower layers might stay soft:

It is an old video from my self built delta printer to tune the flow and pressure advance. I was surprised that the last 5 layers are still moving although the cooling was quite strong. Therefore I learned this material needs a layer time of more than 12 seconds to get the layer underneath hardened enough. For more massive parts the minimum layer time increases as the heat can not dissipate as good as at the single wall part in the video.

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3D printing is often an optimization game. What improves one failure mechanism can easily worsen another failure mechanism.
Cooling helps to quickly “freeze” a geometry, so it is great for improving drooping and bridging. Keeping the most uniform temperature possible however will help with warping, both global and local.

With PLA, I expect you’ll see the biggest improvement by going slower and reducing acceleration on a calibrated filament. After that, you are at a point where tweaking temps and cooling can be effective.

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Thanks for your explanation. Interesting to see, that ~5 layers stay that soft for so long time.
Yeaterday I did some more testing. After manually calibrating the filament, I printed this part:

Looks a bit better overall but the main problem still exists. What I now observed is that the problems occur on one of the edges and that´s the one facing away from the cooling fan and at the same time is the one where the seam is placed.

I also came up with the idea to print more at once to stretch the layer time before you wrote your answer with this suggestion, so I printed three at once. But they look even worse so that obviously didn´t help in this case:

Next I tried to print the part with PETG (after manual calibration) but that also didn´t turn out well:

The problematic edge is the same (facing away from the fan and hosting the seam) as before. However the issue looks different to me since the problem here seems to occur not right on the tip of the corner but thereafter. I printed the PETG out of the filament dryer where it´s sitting in right now, could be the case that it has too much moisture because it´s an older spool.

I guess that there is an overextrusion right where the seam is, maybe the printer continues to extrude filament while slowing down for the layer shift and therefore at this place there is a little bit too much material which adds up from layer to layer. And it gets worse when I print more parts at once because it´s even slower when the printhead has to move from part to part and start a new layer. Maybe the filament flow isn´t reduced enough in that moment?

I just reoriented the part and manually painted the seam. I oriented the part with one edge facing to the fan, in this way no edge is completely covered from the airflow of the fan. Also I painted the seam onto the corner that faces to the fan. I also moved the part completely to the left of the buildplate centered directly in front of the fan. Door and lid open. Here is the result:

Looks way better. Next i placed four parts in a row in front of the fan all in the same orientation. Here the result:

The right one has issues, the part warped and has an error in one of the lower layers. It was just barely sticking to the bed but I was lucky it finished. It was the one that was placed most into the printer so the most distance to the front door. I´m now running a second round of four and the back part has the same issue again, the rest look fine so far.
So in summary I guess as @heapstar pointed out this part needs tons of cooling to be printed properly. Maybe it would even make sense to place another fan in the back of the printer for parts like these or bigger ones that cannot be placed next to the open front door.

I think you are doing really well in your troubleshooting approach. Methodical and stepwise. :smiley:

Going with PETG on a print that did not work satisfactory in PLA is ambitious though. PETG is worse for warping than PLA and the Bambu stock settings for Bambu PETG need “some” tweaking regarding cooling. There are quite a few threads here for PETG which go into further depth. If a print is already warping noticeably and suffering from drooping with PLA, then it most likely will not work better with PETG.

There are also two more key items that you can try for a perfect print.

  • In order to keep print temp but increasing local cooling, you can go slower. In my case, I always reduce speeds and accelerations quite a bit but then as a hobbyist, I can afford the wait. This usually prevents a whole bunch of problems for me while also increasing part cooling (using the part fan in the print head).
  • In order to reduce the heat input per layer (and hence warping) you can reduce layer height. Try adaptive layer height. I really like that feature as it allows wall angle dependant trade-offs between quality and time taken.

It also looks like you succesfully removed the seam issues. Perfect :grinning:

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