Curling on Overhangs and Temperature

I've been having trouble with overhangs curling up now for a while, and nothing I do seems to fix the problem. If the overhang is large enough, the curl will build up to the point where the print catches on the hot end and either pulls the part loose or causes the motors to skip.

I've tried slowing the perimeters waaaay down, using a cooling fan, installing a duct (http://www.thingiverse.com/thing:21490), and changing layer heights. I'm starting to wonder now if my problem has to do with my print temperature?

Do any of you guys have a feel for how bed and hot end temperatures affect curling? I'm currently printing PLA at 200C for the first layer and 185C for the rest, with the bed at 70C for the first layer, and 65C for the rest.

Thanks for any input!

I don't use a heated bed but I believe I've read that the bed needs to go below the glass transition temperature after the first layer which would be around 55c so maybe try lowering the bed another 10c?

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Hmmm, I'll give that a try. From Wikipedia, the glass transition is when the material transitions "from a hard and relatively brittle state into a molten or rubber-like state". I could see that making the lower materials softer and more prone to allow curling.

I'll let you know if switching the bed temperature to 55C for the upper layers fixes my issue.

Thanks

If that doesn't fix it you might try stretching the filament less. I.e. extruding closer to the die swell size that your nozzle gives.

Edited 1 time(s). Last edit at 05/22/2012 03:35PM by nophead.

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[www.hydraraptor.blogspot.com]

Nophead, if I understand you correctly, I should measure the width that the nozzle extrudes in free space, then choose W/T so that I'm extruding the same cross-sectional area?

Thanks

Yes, or a little bit less to have some tension for overhangs but not too much to curl up edges. It might help, I am not certain.

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Thanks Nophead, that seems to have mostly fixed it. To quickly get this working, I just changed my layer height in Slic3r from 0.15 to 0.3 (I have a 0.5mm nozzle), and it's curling much less now. I think I'm going to swap out my 0.5mm nozzle for a 0.35 so that I keep my resolution high without this curling problem killing me.