PLA curling on overhanging corners

Hello,

I have been struggling with overhanging corners for a while now. What I am trying to do is print out gears like this but I have had this problem on other projects as well. The problem that I have is that the tips of the corners curl up causing the head to hit and either dislodge the print or skip teeth on x and y. I am unsure as to what is causing the problem. I am using a reprappro huxley with a .5 mm nozzle. I also have .3 nozzle for it.

Here are some of the things that I have tried:

Layer height. This has been the most effective thing That I have tried. The only way that I have partially succeeded is to increase my layer height to .48. This seems to work because the molten plastic sticks out so far that instead of curling up it sags for a bit then curls up to level. I have tried going to a .1 mm thickness but that did not help any.

Temperature. I have tried everything between 190 and 210 without much success. the higher temps seem to work a bit better.

Amount of material. I decreased my extrusion multiplier to the point that my prints were not even bonding but this only delayed the curling for a couple of layers.

Nozzle size. So far the .5 mm has worked better than the .3 mm.

Filament. I have been using black PLA pro from MatterHackers.com

I have exhausted my ideas for what to try next. I have tried many combinations of the above options over the course of several days and yet cannot get it to print. This print is clearly possible because others have done it. My problem seems to be either the plastic is curling (how do I fix that). Or the extruder is consistently putting too much filament at the tips of the gears (how do I fix that). It seems like the plastic is too elastic after extrusion.

The picture that I attached is a print that I killed early because it had already started to curl. I have many many many more failed prints if more pictures would help.

Thanks for any help you guys can give me,
David

You need a fan blowing on the print. Also, with small parts it's best to print 2 at a time to give each part time to cool before the next layer.

Edited 1 time(s). Last edit at 11/16/2013 03:08AM by waitaki.

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Waitaki 3D Printer

I actually have a small fan mounted to the x axis carriage like this. Is that little fan not enough or do I need a fan blowing on the entire area? Should I try printing hotter or colder?
Thanks for the help!

A fan blowing on the bed helps a lot, but doesn't fix it in my (limited) experience. My theory is that there's not much mass of plastic in overhanging sharp tips like those teeth, which means the nozzle is able to heat up the whole thing as it passes over, even if the plastic had been cooled to room temperature by the fan. And since the supporting mass is all hot and melty again it easily deforms as the top layer cools and contracts.

What speeds are you printing at? Faster speeds could help by reducing the amount of contact time during which heat can be transmitted into the part. You still need the layers to cool as you print, and with the faster speed you'll probably want to aim a powerful fan across the whole bed.

I had not thought of that. I am currently printing at 30 mm/s. Maybe if I tell it to print the infill at 20 mm/s instead of 60 and then raised the printing speed to 45 mm/s that would give me faster perimeters while allowing them extra time to cool. I am also going to try lowering the extrusion temperature to 185c becasue the manufacturer says that it will still extrude at that temp. I will also try to locate a floor fan or something like that and have that blowing across the entire area as well. maybe with all of that combined it will actually work.

Those new numbers sound sensible to me, though maybe keep the infill a little faster. You could also try bumping your external perimeters up to 100% speed instead of 70% (or whatever the default modifier is) since this will be the perimeter with the most overhang.

Unless they've changed since I bought my kit those RepRapPro nozzles are very squat, meaning they can transfer more excess heat into the already printed layers. If you continue having trouble then perhaps buying a more pointy nozzle tip will help. They're pretty cheap.

I'm no materials engineer, but lowering the extruder temp beyond a certain range *might* make it worse, particularly at faster speeds. With less energy/heat the polymers may have a stronger "desire" to return the extruded filament to its original shape - shorter and fatter - pulling harder on the teeth.

Thank you 4Mule8! Your suggestions solved the problem. I raised the speed up to 45 mm/s and raised the temp up to 195. I also put a much larger fan blowing directly on the print bed and with that combined I can now consistently print those overhangs. Thank you very much!

Woohoo, I'm glad it worked!

I've done a ton of printing and was relatively new to PLA until recently.
I just could not for the life of me get the edges of the robohand parts to stop curling (https://www.thingiverse.com/thing:44150)

I tried double fans, higher temp, faster perimeters, lower multiplier, nothing worked with slight tweaking to these parameters

I had to increased the temp to 205! (for PLA I didn't think it should go that high!) but again with two fans so that might affect it.
I might try the next part with one fan and see if thats too hot.
I think the point where the overhangs sag and look bad is probably the point where heating is too high or there is not enough cooling.
I think the key is getting it hot enough to completely melt it so it doesn't try and return to its pre-stressed shape.
I'm cross posting at (http://forum.velleman.eu/viewtopic.php?f=51&t=10632) the other best discussion on this ive found.

Someone brought up too much cooling might cause this but I dont think thats it.
I've seen cooling on the first layer cause peeling, but not the same thing.
I originally started using 2 fans because I was printing threaded bolts and with only one fan, only one side had adequate detail

I won't add some clarity to the solution but I'll add some issues that derive too from this up-curling on the overhang corners.

Note: I'm speaking about ABS printing but..I suspect the topic is similar to PLA...

Axis shift !!!
The up-curl get's solidified and sometimes the nose hit's it and it's a hard hit so the Stepper motor does a Skip. And the whole object get's shifted .. a little.

I'll also add that in the end, I don't think there is an universal solution.
In the end, each (complex) object will have a "preferred" set of parameters that will work on a "particular" printer.
Changing the object or the printer might change these parameters.
THIS is the reason that I believe that there is a long way till the "print'n'click" printers.


Coming back to the solution, I'll add that:
- higher temperature helps the gravity win the fight of hot-end attraction
- higher speed isn't necessary a good solution. If the hot-end hit's a bump, if it's slow and hot might "melt" the bump. Otherwise... skipping can occur.
- as for the fan, "hot'n'windy" also helps. It "freezes" the material as soon as it gets out of the nozzle.



In the end, the journey to a good (perfect?) print is also fun.... in itself...

I'll follow this topic so keep posting.

:-)

Edited 1 time(s). Last edit at 09/21/2014 12:58PM by alexella.