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My supports 'grid' prints with empty spaces (after stoping extraction over perpendicular lines) (BTW. I have checked the direction when it appears and it has nothing to do with coastig)

enter image description here

(the end result is: extra filament sticks to nozzle forming 'big bomb' and end up with screwed printout due to layers shift)

  • Printer: Qidi X-Plus
  • Slicer: Qidi Print 5.3 based on CuraEngine 2019/09/24
  • Retraction: 3 mm, 30 mm/s
  • Filament: PET-G Spectrum
  • Temperature: 220 °C
  • Bed temperature: 80 °C
  • Speed: 60 mm/s

What could be the reason? This is particularly evident on PETG.

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  • $\begingroup$ this seems to be a result of bad slicer settings. Please tell us: what printer, which slicer variant (YES, we need to know who made it), what filament type at what temperature, what retraction length and speed you use. $\endgroup$
    – Trish
    Apr 24 '20 at 14:49
  • $\begingroup$ Printer: Qidi X-Plus Slicer: Qidi Print 5.3 based on CuraEngine 2019/09/24 Retraction: 3mm, 30mm/s Filament: PET-G Spectrum $\endgroup$
    – Mac
    Apr 25 '20 at 19:55
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    $\begingroup$ Please update the question by edit and add even more relevant data like print temperatures, speeds, printer brand and model, etc. Without such information it might not be possible to solve this question. After editing, we can reopen the question. $\endgroup$
    – 0scar
    Apr 25 '20 at 21:35
  • $\begingroup$ what's the print Temperature? I strongly suggest to use proper Cura instead of the Qiditech reskin - it is impossible to know which version and derivate really was used and which bugs to steer around $\endgroup$
    – Trish
    Apr 26 '20 at 5:58
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You mentioned coasting. Absolutely make sure that's off. Coasting inherently extrudes less material than what's needed to print the model correctly, and this underextrusion will accumulate. PETG is really sensitive to underextrusion because it doesn't self-adhere well without a lot of effort to get things right (temperature, speed, etc.) and unless/until the amount extruded is enough to adhere well, it'll just get dragged by the nozzle.

Also 220°C is way too low for PETG, and low temperatures will exacerbate this kind of problem. I'd consider 230°C the absolute minimum for PETG, and 240-250 preferable. Ignore what the filament manufacturer or vendor advertises about lower temperatures being okay; this is normally a marketing ploy to ensure they can sell to users with printers that don't recommend high temperatures or have hard limits in firmware and users who are worried about PTFE off-gassing when operating at higher temperatures (not a real issue at or below 250°C, and probably not even up to 260-275, but still common FUD). Even if they don't want to be deceptive they're competing with other vendors who do.

Further, make sure fan is off, or at least set to very low speed. Rapid cooling will completely mess up PETG adhesion. PETG is still very viscous at printing temperatures (unlike PLA) so there's no need to start cooling it right away to ensure it keeps its form.

Finally, PETG is just a real pain to print with. At first I thought it was a nice material, because it holds shape well and can stand up to fairly high temperatures (which are still true), but there are lots of gotchas and it's really hard to tune your settings to get good adhesion and strong parts. Be prepared to do a lot of experimentation beyond the things I've written in this answer to get good results if you want to keep using it.

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