No nice PLA overhangs despite lots of cooling

I am having troubles with printing steep overhangs with PLA. Most advices on the forum says more cooling so I have put three 120 mm fan blowing on the print (from the left, right and top) and turned of the bed heating after the first layer. I am printing with 0.2 mm layers and have calibrated extrusion, leveled bed etc.



I am trying to print the overhang test seen in the attached pictures, but only down to 35 degrees turns out OK, the major problems seems to be upwards curling. The perimeter speed was 30 mm/s but I have also tried to print at half the speed with worse results as a consequence. My PLA temperature is 170, lower than that and I start having problems extruding it.

I think my printer can do better! Any advice what to try next?

Upwards curling is due to the top layers contracting during cooling.

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So your suggestion is to reduce the cooling? I've heard a lot of people saying PLA cannot be over-cooled. Or maybe without heated bed if it will stick anyway...?

Edited 1 time(s). Last edit at 01/23/2015 05:08PM by Ploks.

On overhangs curling up is caused by too much cooling. Those other "people" just don't know what they are talking about. This is the reason you can control a fan with the software, I never print with more than 60% fan or my nozzle starts to run into the rising PLA.

My printer has no cooling fans. But when I print with pla, it curls upwards on overhangs. When I point a desk fan at it though, the curling is reduced. I think its all about finding the perfect balance between too little cooling and too much cooling.

Thanks, I will experiment with less cooling. Do you guys keep the fan running over the whole print or just during short layers, bridges and overhangs?

You want the fan to start on layer 2 and for the rest of the print. You don't want it on layer 1 as it's not needed and not having it helps filament stick to the bed.

Still can't get this to work. I have tried lots of cooling, almost no cooling, heatbed on/off after first layer and changing the hotend temperature. No matter what, the overhangs will curl upwards

Edited 1 time(s). Last edit at 02/08/2015 08:28AM by Ploks.

Did you find any solution?

Alas, no

what temperature are you printing at?

In the initial post it says 170°...

Do I have tso suggestions for you as I am suffering from the same problem!

- I noticed that lots of cooling helped somewhat - but also increasing! The print temperature to about 210- 220° which was more then I usually printed PLA at. Whoch software are you using?
In Slic3r try to adjust the "external perimeter width" - try to go bigger then your nozzle diameter.
changing this from about 0.4 for my 0.4 nozzle to 0.6 or even 0.7 or 0.8 on steep overhangs did the trick for most of the parts I was having trouble with.

also you want the air not just to be pushed all around your hotend with severyl 120mm fans bit to be directed exactly where the fresh extruded plastic xomes out of the nozzle.

i also insilated my heaterblock - so it will not react towarda the nassive cooling with heating upnunevenly...
a small layer of high temperature silicon is what I can recommend.

that red stuff is heat proof to 260° or 300° for shorter times.

hope this helps a bit.
please post your results,

Alex

Hi,

indeed I usually print at the lowest possible temperature but not always (my red PLA requires higher temperature to stick properly). I seldom try as high as 200 degrees but I will run some test today, doing that as well as changing the perimeter width.

Thank you for the suggestions!

Quote
Alexander1984
In the initial post it says 170°...

Do I have tso suggestions for you as I am suffering from the same problem!

- I noticed that lots of cooling helped somewhat - but also increasing! The print temperature to about 210- 220° which was more then I usually printed PLA at. Whoch software are you using?
In Slic3r try to adjust the "external perimeter width" - try to go bigger then your nozzle diameter.
changing this from about 0.4 for my 0.4 nozzle to 0.6 or even 0.7 or 0.8 on steep overhangs did the trick for most of the parts I was having trouble with.

also you want the air not just to be pushed all around your hotend with severyl 120mm fans bit to be directed exactly where the fresh extruded plastic xomes out of the nozzle.

i also insilated my heaterblock - so it will not react towarda the nassive cooling with heating upnunevenly...
a small layer of high temperature silicon is what I can recommend.

that red stuff is heat proof to 260° or 300° for shorter times.

hope this helps a bit.
please post your results,

Alex

Today I printed the calibration piece (see first post) and managed to get all but the last 20-degree overhang to print nicely. I put the perimeter width to 0.8 mm which improved the overhangs greatly, just as you suggested. Increasing it to 1 mm did not yield further improvement. Might try 0.1 mm layer height and see how that behaves later on.

The reason I do not have a smaller fan blowing at the nozzle opening is that I have not managed to print a fan duct that gives me a significant flow. Of some reason most of the air from the fan bounces and escapes backwards :/

This is the first major progress regarding my printing for quite some time, thank you!