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Strange under/overextrusion


Dim3nsioneer
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Posted · Strange under/overextrusion

Hi there

This is a very strange one. I tried to print http://www.thingiverse.com/thing:14195 in Colorfabb signal red PLA/PHA. After having measured the filament diameter I-don't-know-how-many-times I set it to 2.85mm in Cura 13.12-test (worked nicely for other prints).

After a few prints with serious underextrusion I also managed to get some fairly reasonable settings (not fully convincing quality) such as 50mm/s at 220°C with more or less closed surfaces.

Then I scaled the model by 2 in z-direction, i.e. the thickness was set to 5mm from previous 2.5mm. I was actually baffled by the result.

Snowman Over-Extrusion

The print is 'normal' (which means about the same quality as the original 2.5mm print) up to 2.5mm. After that point, an enormous overextrusion happened.

I put this into the Cura section as I think it is rather a software than hardware issue (would be quite a coincidence if my Ultimaker decides at exact the original height to go crazy, wouldn't it?). However, it could also be the model itself. I just had a look into it and for me, it looks ok...

Any ideas?

 

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    Posted · Strange under/overextrusion

    On some of my prints a few weeks ago, something similar was happening - I think Cura was pre-emptively raising the nozzle temp, in anticipation of the fan being turned on full blast (and thus cooling the nozzle somewhat).

    Did you watch the nozzle temp when this happened? I bet the temp spiked and you started getting overextrusion.

     

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    Posted · Strange under/overextrusion

    Unfortunately, I was not watching it as my Ultimaker behaves usually... :eek:

    EDIT: I turn on my fan on layer 2 (at 100%) and let it run until the end of the print... but I'll keep an eye on that temperature during the next attempts.

     

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    Posted · Strange under/overextrusion

    Cura does not change temperatures during the print. It does change fan speed and printing speed.

    I've put the same print on on a machine here, to see if I get the same issue.

     

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    Posted · Strange under/overextrusion

    Thanks for testing! I'll do another one myself. Maybe it was a big coincidence and a different reason...

    EDIT: How did you get the space between the hole in the hat and the hat outline filled? Seems to me a bit like a mission impossible with a 0.4mm nozzle...at original size.

     

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    Posted · Strange under/overextrusion

    No idea, just downloaded the model, put all settings on default, enabled brim, scaled the Z*2 and printed it.

     

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    Posted · Strange under/overextrusion

    Must be your magic hands then... :wink:

    I printed it again this morning. It came out ok (with the exception of the hole in the hat). So it was definitively something hardware-related. After having another look at the failed print, I think it might be caused by partial delamination as the print is significantly thinner at one end (and the material difference most probably distributed over the rest of the print).

     

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