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While printing PET-G (@ 220 °C nozzle and over 58 °C bed temperature), the outlines always print fine but the infill keeps shoveling. Could I be printing too hot or too cold? I am using a 0.8 mm nozzle.

Shoveling is when the plastic is over extruding to the point at which it starts piling up in the path of the nozzle, usually resulting in an uneven surface. Visually, it manifests like a snow plow shoveling snow. I tried adding an image, but, the filament is black so that turned out to be a difficult task.

This reason why this is a problem is because the nozzle hits those peaks while printing, which seems to be causing the print to detach from the bed. I've also noticed the print curling up at the edges, but I think that's a separate problem.

I am printing at 3000 mm/min. The outline, and the infill is 80 % of that. The layer height is 0.6 mm

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Normally, what you're calling shoveling is caused by having the bed too high - when you deposit enough material for a space that should be the nominal layer height high, but significantly less volume is available, it has nowhere to go but up around the edges of the nozzle.

However, in your case your temperatures are also seriously wrong for PETG. The normal recommended range of nozzle temperature for PETG is 230-250 °C, and in my experience, you need the full 250 °C to have any hope of printing fast. At 220 °C I'm really surprised you're not having problems with underextrusion instead.

The bed temperature is likely even more important. Minimum bed temperature for PETG is 80 °C. If the material is hitting a 58 °C bed as it comes out, it's likely to cool way too fast. This may lead to what you call shoveling (especially if you see both pits and ridges rather than just ridges), but even if not, it's going to prevent the material from bonding to previously laid down lines, so that your print will end up more brittle than PLA.

One additional detail I initially missed involves your 0.8 mm nozzle. It might be hard for the hotend to keep up with properly melting that much PETG at normal print speeds. As noted in the comments, a 50 mm/s linear extrusion rate with an 0.8 mm nozzle is equivalent, in volumetric extrusion rate, to a 200 mm/s linear extrusion rate with a typical 0.4 mm nozzle, which would be extremely fast for PETG. It's unlikely that any hotend except a "volcano" or similar (with extended melt zone length) could keep up with raising that much material to 250 °C that quickly.

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  • $\begingroup$ I upped the temp but it didn't work. Had to strip the pva off the bed, retram and try again. Still didn't working. Changed settings. Still getting problems. I think I'll retire the 0.8 nozzle. $\endgroup$ – user77232 Jul 16 '19 at 14:35
  • $\begingroup$ @R, So heat up, slow down and reduce the layer height or upgrade to an all metal hotend (e.g. e3d) $\endgroup$ – user77232 Jul 16 '19 at 17:00
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    $\begingroup$ @user77232: "All metal" is not what makes a hotend capable of doing high extrusion rates. It needs a longer melting zone and maybe larger heating element. The "volcano" and similar models are the ones to look at, as I understand it. $\endgroup$ – R.. GitHub STOP HELPING ICE Jul 16 '19 at 17:19
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    $\begingroup$ I slowed down and cut the layer height in half. That seems to have solved the problem. I have other problems though. $\endgroup$ – user77232 Jul 17 '19 at 14:56

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