What to do against curling PLA overhangs?
 

What to do against curling PLA overhangs?  

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mavu
 mavu
(@mavu)
Estimable Member

Hello,

I have seen this topic creep up a couple of times, and I would appreciate some help to get to the bottom of it.
I'm not sure why some people seem to have the issue, others dont, and that despite all (most) of us having the exact same printer.

This seems like a opportunity to try and find out whats different between people having PLA curl on overhangs, and those fortunate not to have it.

I'll add a picture of this model from thingiverse: http://www.thingiverse.com/thing:1709106
I printed the *coils and *circle version, and both exhibit the behaviour you can see below.

S

As you can see, the overhang on the side behind the nozzle curves up, while the front overhang (which is identical) doesn't.
If you print the long (snake coil) version, you will see the curling happening more on the right side of the printer, and less on the left, and more on the back side of the print, than at the front.

I have a similar issue with for example this print: http://www.thingiverse.com/thing:1563995

The fins of the rocket have overhangs until they meet the body of the rocket, and due to curling up and the small footprint, it they get knocked off the bed and the print fails.

Both models were sliced with slic3r, Prusa edition, RC2. With the default settings for PLA, 0.2mm and with Z-hop.
I didn't change anything in the settings.

I can get the snake to print, If I reduce the printing speed to 50% (during print, reduce speed with the dial on the printer)
I tied various other things, like higher and lower filament and bed temperatures. 100% fan speed, reducing extrusion modifier, etc.

The printer is in a room thats currently rather cold at about 12-15 degrees Celsius.

Could someone try to print the Snake_coil.stl from above link in PLA, and tell me if they can get it to print with default settings? Its no a very long print, and the curling shows up at about 30% into the print, maybe 30-40 minutes at default 0.2mm.

Any Ideas what I can do to get this under control?

...
Posted : 02/01/2017 10:39 am
david.b14
(@david-b14)
Honorable Member

Just throwing out an idea as food for thought. Can you throw a plastic container over the MK2 which will increase the air temp? I'm wondering if the model is cooling too fast.

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Posted : 02/01/2017 11:47 am
david.t2
(@david-t2)
Noble Member

Set a bit lower HE temperature (210 instead of 215), turn the object around Z axis so overhangs aim towards front edge of the bed and set 100% cooling fan.

Posted : 02/01/2017 11:53 am
mavu
 mavu
(@mavu)
Estimable Member

Set a bit lower HE temperature (210 instead of 215), turn the object around Z axis so overhangs aim towards front edge of the bed and set 100% cooling fan.

I allready tried the Hotend temp at as low as 204 (because the knob didn't let me dial 205 🙂 )

I also tried 100% fan. makes no visible difference.

Turning the model on the plate won't help, becuase the overhangs are on both sides, and the model is curved. Some parts will always be oriented towards the back.

The rocket is the same. 4 fins, 4 directions. no way to turn it so all get hit by the fan from the front.

Also, I'm not even sure its a fan issue, maybe its slic3r related? or something in the settings? No Idea, thats why I was hoping some other people here would attempt to print it, and see if everyone has issues with this model and overhangs in PLA, or just some people.

And then find out what the difference could be.

edit: I'll try to find a box to put over the printer. and try that.

...
Posted : 02/01/2017 12:40 pm
stephan.k
(@stephan-k)
Reputable Member

100% fans is better when trying to fight curling of PLA, you want less heat not more heat.

Lower hotend temperature, try 200 ~ 195. Since this happens pretty close to the bed, reduce bed temperature as well.

Try different layer heights as well..

Posted : 02/01/2017 2:09 pm
mavu
 mavu
(@mavu)
Estimable Member

100% fans is better when trying to fight curling of PLA, you want less heat not more heat.

Lower hotend temperature, try 200 ~ 195. Since this happens pretty close to the bed, reduce bed temperature as well.

Try different layer heights as well..

I'll try to go lower with temperature, but I can't go lower with the bed, or I lose adhesion, because the room around the printer is too cold.

I wonder, if its a temperature problem, why does it work if I print at 50% speed?
The nozzle is over the overhang areas even longer, and should heat up the surounding plastic more.

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Posted : 02/01/2017 4:43 pm
stephan.k
(@stephan-k)
Reputable Member

Yes, too cold on the bed and adhesion starts becoming a problem

I am not sure about the validity of this, so take it with a grain of salt: I had asked around alot about curling on overhangs. I got told:

"when you print slower, the fans have more time to cool the area down."

(One would think you get added heat from longer exposure to heat radiating from the hotend). So at this point, my head started to hurt 😉

"..and when it comes around again to put the next layer on top the already printed layers cooled down even more."

Now, some slicers have a setting fer "minimum layer time" to slow down printing to give it more time to cool, so there's gotta be some truth to it. (Others suggested: get a desk fan and point it into the printer, that i didn't want to try).

Now, I can confirm that minimum layer time / slow down helps when you run into inefficient cooling problems - which seems at least in part responsible for curling as well. But in the end, what worked consistently for me personally with PLA curling was layer height and 100% fan speed. Sometimes thicker layers, sometimes (with steep overhangs) smaller layers. And some PLA tends to curl more than others.

This is where things get tricky i guess 😉

Posted : 02/01/2017 5:14 pm
PJR
 pjr
(@pjr)
Antient Member Moderator

Print slower so that the cooling fan has more time to do what it needs to do.

Peter

Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage…...
Posted : 03/01/2017 7:44 am
christopher.d
(@christopher-d)
Active Member

So with PLA more cooling is needed to reduce curl? I thought the material curled do to cooling too fast?

...
Posted : 21/04/2017 12:03 am
PJR
 pjr
(@pjr)
Antient Member Moderator

I thought the material curled do to cooling too fast?

So try printing faster and watch the curl!

If you let PLA cool by itself, you will get the curl. Cool it quickly by printing slow and it simply won't have time to curl.

The fan is not ideal, only blowing from one side and onto a relatively small area.

Peter

Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage…...
Posted : 21/04/2017 10:41 am
metacollin
(@metacollin)
Eminent Member

So I recently ran into this same problem, and Peter has it right, though a typo makes it a bit unclear :). (Cool vs curl).
Moderator edit: the post containing this error has now been corrected. Thanks metacollin! Peter

It’s important to keep in mind that anything that has a glass transition temperature, is, in fact, a glass.

A glass is basically something that has a certain minimum energy arrangement it wants molecules to arrange in, but it takes a long time for this to happen. Like on the scale of minutes or even hours.

So a glass is something that you can cool so fast that it doesn’t have time to arrange itself and gets “frozen” in place. This is why you can anneal prints to make them stronger - you’re heating it up just enough that it can arrange itself and relieve internal strain.

PLA curling is caused by insufficient cooling at the nozzle, as well as, ironically, too MUCH cooling elsewhere on the model. Cooling causes contraction of the model, which will pull on other parts as it cools. This isn’t really an issue when it’s pullig on more, slightly less cool but solid PLA.

It’s when it pulls on PLA still hot enough to be deformed that you get curling.

Let me walk you through the sequence of events that lead to curling:

You have built up several layers of your print, and the previous layer has cooled faster than is ideal. As the print head nears, it extrudes some hot PLA, but perhaps a poorly nozzled print fan and high print temperatures cause the PLA to not be cooled below it’s glass transition temperature (freezing it) by the time the nozzle has moved elsewhere. Meanwhile, this fan is blowing on the rest of the solid but hot model, cooling it and causing it to contract, which deforms the still-pliable PLA that was just extduded.

If you cool it quickly enough, it solidifies before it can be deformed. The internal strain that would have caused the curling is still there, but it can’t over power the strength of the PLA.

Of course, the faster the model overall cools, the larger and stronger the contraction, and so the stronger the pulling force.

It’s...complex :). The best is to selectively slow down print speeds and double check that your blower fan is blowing mostly at the nozzle where the plastic extrudes and not blowing down onto it he model.

Slowing down infills will have little effect, but slowing down perimeters and small perimeters should help. Also minimizing drafts even with just a paper bag will help.

Another option that is model dependent is using a very high bed temperature - 70 degrees+ for PLA. This is more of case by case solution though

Posted : 24/01/2018 5:26 pm
rbojanssen
(@rbojanssen)
Eminent Member


So I recently ran into this same problem, and Peter has it right, though a typo makes it a bit unclear :). (Cool vs curl).

Thx for the good read, gonna try this out. Running into this problem now when printing the T-Rex model 🙂

Posted : 20/07/2018 1:18 pm
PJR
 pjr
(@pjr)
Antient Member Moderator


So I recently ran into this same problem, and Peter has it right, though a typo makes it a bit unclear :). (Cool vs curl).

Thanks for that. Now corrected for any new readers...

And FWIW, KISSlicer now slows down the print and increases the fan automatically for any paths partially or fully unsupported.

Peter

Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage…...
Posted : 20/07/2018 1:40 pm
hugo.b6
(@hugo-b6)
New Member

I've been trying to address this same issue since I first built my MK3. I can get relatively good results with 0.15mm layer heights. Below that, the corners start to curl up if they are at an overhang or when they are a sharp turn like the OP mentioned. I have literally tried everything beneath the sun with settings in slicer, but to no avail. I have been trying to print the 'Treefrog' with layer height 0.1mm, 0.09mm, 0.08mm, 0.07mm , 0.06mm or 0.05mm, but with every PLA or ABS or PETG or whatever fancy co-polymer, the corners and overhangs always curled up. I have a whole army of frog legs and bellies, the front legs are always curled and rippled badly and the belly is always scuffed, no matter what heat or speed or cooling or tricks. I tried the E3D silicone nozzle sleeve, also not much difference.

In my search through hundreds of threads, one tip came to me that has been my savior: use a smaller nozzle than the standard 0.4mm I have found a dude that makes an adapter E3D nozzle that you can screw 'airbrush' nozzles into:

https://well-engineered.net/index.php/en/shop/airbrush-nozzle-adapter-set
or
https://youprintin3d.de/hotendszubehoer/e3d/duesen/1.75mm/829/airbrushduesenadapter-mit-3-duesen-fuer-e3d-v6-hotend-1.75mm.html?number=airbrush-kit

Using the supplied 0.3mm nozzle that comes with the kit, I could immediately print Treefrog successfully at a layer height of 0.07mm without any marks, just a perfect print! Printing at 0.05mm was also 99% perfect with some small rough spots, but a thousand times better than with the standard 0.4mm E3D nozzle. Using the 0.2mm airbrush nozzle (which was easily cold swapped with a small pinch pliers) I can now even print the Treefrog perfectly at 0.05mm layer height! And small details like text on the back of Benchy is even readable.

I think the reason is maybe that the smaller nozzle makes narrower paths, that don't overhang so much, AND that the sharp, long, airbrush tip doesn't heat up the old layers when passing.

I hope this information might help a lonesome PLA curling warrior out there on his endless battle. For me, the airbrush nozzle has now allowed me to print at any layer height, with any PLA with any temperature, without any curling on sharp corners or overhangs!

Posted : 12/10/2018 12:06 am
foo.b
(@foo-b)
New Member

While searching for the same issue, I found also this thread
https://reprap.org/forum/read.php?262,117402,119574#msg-119574
The rather unusual solution of increasing extrusion width to ~150% worked like a charm.

Posted : 01/01/2019 7:40 pm
niels.v5
(@niels-v5)
New Member

Hi,

Well I'm using a Ender 3 so i don't know if this is going to help you. I have the same issue with the curling on overhang and if it does have to do with insufficient cooling maybe this will work, I don't know if something like this exist for a Prusa but this could be a solution

https://www.thingiverse.com/thing:2912394

Posted : 08/01/2019 12:08 pm
JVEnterprises
(@jventerprises)
Eminent Member

Hi,

I read this chain, and tried everything inside, but still am not getting acceptable results. I was wondering if anyone had anymore information?

I am trying to print the moon city here ( https://www.myminifactory.com/object/3d-print-52920 ) at 100%. Basically I can't get above the 10mm mark without the overhang area on the front curling up and catching the nozzle.

First I tried slowing things down 50% from the prusa PLA defaults in slic3er. I did see some improvement, but not enough to call ti a success. I tried rotating the design a bunch of times in an attempt to separate cooling from other print issues, and found that the trouble area always stayed in the same area, so in my case I don't think its cooling.

I don't understand the thread where it talks about height /width ratio begin set to 150%. I am printing with a .4mm nozzle, .15mm layer height, and slicer has the width set to .45mm by default. That is 300% now, am i supposed to decrease the width to .3mm? Sounds like a lot to me.

I am going to try a different brand of material tonight, perhaps that will help. Was hoping others had found the answer. I will also try at .2mm height. Perhaps I am just trying for too thin of a layer with a .4mm nozzle.

I should mention that minus this curling problem my prints are otherwise perfect. No first layer issues, no other quality issues, so I don't think the problem is something related to poor calibration.

Posted : 12/03/2019 12:06 pm
shakie
(@shakie)
Eminent Member

I have the same problem.

 

First: I understand the theory of the "freezing glas".

As we all now know, the curling comes from the behaviour of shrinking material when cooling down. The hot material is printed on cold material and shrinks. Like a bi-metal this makes it bend up.

But there is another way to handle it. Simply try to avoid shinking by keeping the material hot.
If you have insufficient cooling, try it with absolutely no cooling. Let the nozzle move very slow (<=10 mm/s) over the outer walls.

The missing cooling slows down the shrinking process. And the slow moving nozzle works like an iron.

Posted : 24/06/2020 7:14 pm
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