Help with Cura settings

[Reverse_Engineer 0]

Reprap printer - cartesian

PETG filament 1.75mm

Cura 3.6

 

So I'm trying to print some parts with that have an open section in the center - a bit like a coffee cup I suppose and I'm getting so much stringing in the center where there should be nothing that it's basically ruining my prints. I've tried playing around with retraction settings, temp settings and travel speed and nothing seems to change. So I observed a print and when the strings are created the nozzle travels across the center of the print to start a new layer but the extruder doesn't retract and filament oozes out until it gets to where the next layer starts.

 

So in my meddling I tried turning off combing and then the extruder retracts during travels and the strings are gone. This creates several other problems that degrade the print quality in other ways, the first layer has problems due to how it stops, retracts and restarts so much. When combing is on the first layer doesn't go through all those stop start retract moves and it works perfect. Having combing turned off also seems to create a lot more blobs both within the infill and on the outside of the print.

 

So is there a way to enable retraction while combing is on?

 

All those travels seem really inefficient when printing something with nothing in the center, that time could be better spent printing something. Is there a need for the nozzle to travel across the print like that between layers and is there a setting to stop it?

 

 

[Reverse_Engineer 0]

So I wasted another 100 metres or so of filament on this print with combing turned off, there was very little stringing until it got near the top of the print and then it seemed to make thicker strings than all the previous attempts.

 

So anyway I viewed the layer view preview with the travels shown and it was generating travel paths in seemingly random places that went across the print where there was no material to be printed (just like the print did), it looked like a spider had moved in and made a web. So then I sliced the same file for another printer I have and all travel paths were confined to places that had material printed, seemingly eliminating the opportunity for strings to be drawn across the void in the print.

 

Then I loaded the model back into Cura with the original profile for the first printer and sliced it again with all the setting as they were when I was having problems and checked the travel paths and this time they are all on printed surfaces. Nothing changed except the way Cura decided to plot the travel paths. So it seems like Cura can sometimes plot the travel paths in a way that leads to stringing across a void.

 

I don't know if it's a bug or just a random slicing error, it's never happened before. I will be sure to check the show travels box when I check the layer view from now on though.