<p>I came across several issues which seem to have been lowered.
Firstly, I changed from a 0.4 to a 0.5 mm nozzle. Because of the backpressure I was not able to print my PETG (Colorfabb XT filament) below 270°C which caused unresolvable oozing. After that I was able to extrude till 230°C.</p>

<p>The left print below shows the result. I disassembled the hotend, there was no leak or whatsoever. Maybe it was too cold for printing. However, the temperature displayed was 250°C. Then I replaced the cheap aluminum heat block with a copper alloy based one. After that my PIDs did not work anymore. I had to greatly enhance the d-term, otherwise there was a big overshoot. Guess there was a serious heat conducting issue with the old BQ hotend. </p>

<p><a href="https://i.stack.imgur.com/uxd43.jpg" rel="nofollow noreferrer" title="Prints using BQ Alu Heatblock (left) and Copper alloy heatblock (right)"><img src="https://i.stack.imgur.com/uxd43.jpg" alt="Prints using BQ Alu Heatblock (left) and Copper alloy Heatblock (right)" title="Prints using BQ Alu Heatblock (left) and Copper alloy heatblock (right)"></a></p>

<p>Anyway, from there it became better. However, I noticed that I still have severe underextrusion after travel moves (second piece, first picture, first piece, second picture). I use Cura, so I activated retraction with the feature to prime after travel moves. I got the wall closed just after 0.35 mm³. </p>

<p><a href="https://i.stack.imgur.com/Oj1Ey.jpg" rel="nofollow noreferrer" title="Prints using Copper alloy Heatblock (left)"><img src="https://i.stack.imgur.com/Oj1Ey.jpg" alt="Prints using Copper alloy Heatblock (left)" title="Prints using Copper alloy Heatblock (left)"></a></p>

<p>My Question: Is this underextrusion after travel moves normal for PETG/XT? I did not discover such behavior with PLA or ABS in the past. </p>

<p>Current Site Advice: Despite the weight, copper heat blocks seem to be worth the upgrade. </p>

[{'answer_id': 7007, 'author': 'Brian Chow', 'author_id': 13062, 'author_profile': 'https://3dprinting.stackexchange.com/users/13062', 'pm_score': 3, 'selected': True, 'text': "<p>Have you tried adjusting the Extra Restart Distance in Simplify3D or Retraction Extra Prime in Ultimaker Cura?  Most slicers should have a similar setting, perhaps named just slightly differently.  A small positive value can help prime the nozzle after a long travel when you've lost back pressure or oozed a little.</p>\n"}, {'answer_id': 10194, 'author': 'R.. GitHub STOP HELPING ICE', 'author_id': 11157, 'author_profile': 'https://3dprinting.stackexchange.com/users/11157', 'pm_score': 0, 'selected': False, 'text': "<p>Zero retraction is just a special (worst) case of under-retraction. You'll pretty much always lose material to oozing if you don't retract before travel. At best this ends up hidden inside the print (but can still affect weight and weight balance); usually it'll also harm the surface.</p>\n\n<p>Ensure that retraction is set to <em>always</em> happen (not skipping short travel), and at least 5-6 mm for bowden extruders. Direct extruders can get away with less but I'm not sure exactly how much less. Less-rigid materials need more retraction to make up for compression of the filament between the extruder gear and the nozzle.</p>\n"}]
['https://3dprinting.stackexchange.com/questions/6315', 'https://3dprinting.stackexchange.com', 'https://3dprinting.stackexchange.com/users/10847/']