mavu
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What to do against curling PLA overhangs?

Mon Jan 02, 2017 9:39 am

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
pla_curling1.jpg
pla_curling1.jpg (838.5 KiB) Viewed 9546 times
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?

david.b14
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Re: What to do against curling PLA overhangs?

Mon Jan 02, 2017 10:47 am

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.

david.t2
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Re: What to do against curling PLA overhangs?

Mon Jan 02, 2017 10:53 am

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.

mavu
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Re: What to do against curling PLA overhangs?

Mon Jan 02, 2017 11:40 am

david.t2 wrote: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.

stephan.k
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Re: What to do against curling PLA overhangs?

Mon Jan 02, 2017 1:09 pm

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..

mavu
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Re: What to do against curling PLA overhangs?

Mon Jan 02, 2017 3:43 pm

stephan.k wrote: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.

stephan.k
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Re: What to do against curling PLA overhangs?

Mon Jan 02, 2017 4:14 pm

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 ;-)

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PJR
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Re: What to do against curling PLA overhangs?

Tue Jan 03, 2017 6:44 am

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 or loss.

christopher.d
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Re: What to do against curling PLA overhangs?

Thu Apr 20, 2017 9:03 pm

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

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Re: What to do against curling PLA overhangs?

Fri Apr 21, 2017 7:41 am

christopher.d wrote: 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 cool.

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 or loss.

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