Cooling Issue... or not?  

Re: Cooling Issue... or not?

Could well be, you can normally tell if the side facing the fan is better. you'll never perfect overhangs facing away from cooling but supports do help.

Re: Cooling Issue... or not?

I've been fighting with this for years, and i could not get it away fully.

Generally it is said that :
- printing slower helps
- lowering filament print temperature helps
- printing with filament fan at full blast helps

I found those 3 above to be only marginally useful for the round and the pointy overhangs. I've tried various combinations like 10% speed and 180 degrees temp and having 1 super filament fan blast at it.

What i found out that also helps a bit:
- room temp needs to be cold, and don't put a printer in a case even with the door open. there needs to be a lot of cold airflow around the printer to help with this. The reason for this is because if there is only the front door open, the filament fan will create a small vortex front the front to the back and blow the same warm air onto the print that it did before. (i measured it with smoke stick)
- Prints work better in the winter, not so good in the summer. even a 5 degree drop in room temp can vastly improve the print quality on overhangs.
- having a new nozzle also helps with this. Using a nozzle that has dozens or hundreds of prints behind it, is not showing the same good results as a new nozzle.
- printing at 80% speed of the stock MK2 0.20 layer profile is best bang for buck in terms of overhang quality and speed
- using 4 walls instead of the normal 2 also helps.
- printing in larger layer heights (0.35) works much better than lower layer heights. (0.1 on round or pointy overhangs is often impossible.
- switching off the heated bed after the first layer (to ensure it sticks) is also a good idea, provided you print with a big brim.
That way the filament fan wont cool the parts with hot air from the bed.
- some filaments work better for round or pointy overhangs than others
- PETG works better than PLA for overhangs, too

Also not everything can be printed cleanly, i gave up on printing a few models as perfectly as possible, It's just not possible with some models.

Will be keeping an eye on this topic.

If you are feeling adventurous, print this: https://www.thingiverse.com/thing:2151369 or this: https://www.thingiverse.com/thing:2768971

Re: Cooling Issue... or not?

Damn...
That was a really accurate and helpful information from your experience.
I think this topic can help a lot of us wirh overhangs and we do not need to run as much tests by our own.
I will definitive try out your tipps and will let you know the results.
Thanks for that explanations - they are all clear and easy to try.
I have the printer in an open enclosure so I will put the printer out and gove that a first try.

I hope someone else can try similar prints what I did just to see if that is a printer issue or something else.
I am quite sure that specially the heart should work flawlessly because the overhang is not quite big.
I had also other prints with 45 degreee overhangs which worked good higher on z but bad on low z values.
I will do some tests as soon as I can, maybe meanwhile We will get some experiences from others on the MK3 because a lot of models has at least 45 degree overhangs.

Re: Cooling Issue... or not?

The reason for a slightly worse print quality in an enclosure is because if there is only the front door open, the filament fan will create a small vortex from the front to the back and blow the same lukewarm air onto the print that it did before. (i measured it with smoke stick) You'd need to a big fan on the back of the case thats running with the open door, or you'll just create a heat dam (don't know the wording for this in english)

Also the overhangs can be put into 3 categories:

- flat overhangs: https://www.thingiverse.com/thing:261317 - these print really well, on my Prusas i can manage even 80-85 per cent very well. Only 90 looks not so good. this is because straight overhangs print much better than curved or pointy. reason, i can only speculate like more grip on the longer edges and no round filament shrinkage

- curvy overhangs: https://www.thingiverse.com/thing:2151369 - these tend to look like shit all the time. also why holes are always smaller than designed, because filament, as said above, shrinks and flows inwards when printed in round shapes.

- pointy overhangs: https://www.thingiverse.com/thing:2768971 - these will actually print well if you slow down and print cooler (as long as the new inward walls can piggyback on the last outer walls on the layer below), but the texture around these is always weird compared to the rest of the print. Its looks like it's burned most of the time, even if you print dog slow and ice cold.

Re: Cooling Issue... or not?

I will do these tests with your test changes and see what I can improve.

Never thought about overhangs that much - before it was just an overhang for me - but now I can look on them in a different way and maybe also try to prevent such „worst cases“

Re: Cooling Issue... or not?

I hope someone else can try similar prints what I did just to see if that is a printer issue or something else.
I am quite sure that specially the heart should work flawlessly because the overhang is not quite big.
I had also other prints with 45 degreee overhangs which worked good higher on z but bad on low z values.
I will do some tests as soon as I can, maybe meanwhile We will get some experiences from others on the MK3 because a lot of models has at least 45 degree overhangs.

The real answer is that support in Slic3r does not work well and needs to be fixed. You should be able to add support for steep overhangs and get reasonable print quality.

You can try using a different slicer and see if you get better results.