Strange under/overextrusion

[Dim3nsioneer 557]

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.

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?

 

[nick-foley 5]

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.

 

[Dim3nsioneer 557]

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.

 

[Daid 306]

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.

 

[Daid 306]

 

[Dim3nsioneer 557]

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.

 

[Daid 306]

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

 

[Dim3nsioneer 557]

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).