How do I avoid straight lines for walls in Cura?

Question

I need to print a thin piece. Theoretically, it could work, but Cura prints the walls as single lines. In my case, it is just this line that breaks apart as you can see here.

Is there a setting that would instruct Cura to avoid creating such a line as the outer wall, or how else could I resolve this problem?

• Printer: Kobra Max
• Material: PETG / PLA
• Temperature: 250 °C / 65 °C

Speeds:

• Print speed: 80 mm/s
• Outer Wall Speed: 45 mm/s
• Inner Wall Speed: 80 mm/s
• Top/Bottom Speed: 45 mm/s
• Travel Speed: 100 mm/s
• Initial layer speed 45 mm/s
• Travel retraction speed: 40 mm/s

Answer 1

Outer wall perimeters are printed as continuous lines, unless the geometry determines otherwise.

Your print faces an overhang situation in which it is prone to print walls from the inside out as where it sticking the wall lines together.

Default behavior is printing the outer wall first and traversing inwards, in overhang situations this isn't ideal so that you may want to print the wall perimeters inside out as if you stick the newly deposited perimeter to the latter.

Generally, printing outer perimeter first will give the print better dimensional precision, but, may cause problems in overhang situations where there is limited area to "stitch" your perimeter to, hence the poor adhesion you experience.

A solution is to print inside perimeters first and work outwards, in Cura, there is an option for called Wall ordering to change the order of perimeter printing.

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After updating your question with the print speeds, another possibility that came to mind is that you are extruding too fast for PETG for your setup (extruder and nozzle assembly). Not all extruders can process PETG fast enough or nozzle assemblies cannot heat fast enough causing the nozzle to under-extrude. I've seen this happen on my own printers. Please note that the premium brand I use, limits extrusion to 50 mm/s, 80 mm/s might be on the high side for your setup. It isn't that PETG cannot be extruded fast, it is merely that not all extruders and nozzles are capable of doing so (especially the lower end of the 3D printer market). So even that you now can stick perimeter from changing the order, under-extrusion might prevent from a good adhesion.

Answer 2

I'm pretty sure your core problem is underextrusion from printing PETG faster than your extrusion system can actually keep up with. Unless you've cranked up the acceleration, long straight lines are the only place in a print where the actual print speed will reach cruise at the requested speed; otherwise, all the time is spent speeding up towards that requested speed, then slowing back down for the next turn before reaching it.

If you have a single-flat-filament-gear, no-reduction-gearing, bowden extruder like the Ender 3 and most of these Ender 3 clones have, you'll be lucky to get reliable, consistent extrusion with PETG even at 50 mm/s (assuming 0.4 nozzle and 0.2 layer height). 80 mm/s is almost surely too much without upgrading your extruder.

Also, you didn't say anything about temperature, but low temperature will exacerbate this problem and lead to the failed layer bonding you're experiencing. Anything below 245°C is "very low" for PETG - despite what manufacturers recommendations may say. They write the recommendations low so that customers with PTFE-lined hotends (which can't safely go above 245-250) will buy their product, not because it actually works well at those temperatures.