QUESTION Why is the nozzle still printing out material when travelling?

[hyiu0000 0]

Hi, I just start printing with Cura and Ultimaker 2.  I have built-plate adhesion set to "Raft", and after printing the first raft layer, it travels to the next raft layer but seems like the nozzle is still extracting.  I already have retraction enabled.  I tried different settings such as "Combing mode", "Z hop", etc, and it does not change anything.  If I have retraction enable when layer change, it does retract but it retracts only after drawing the diagonal line.  See the pictures.  The nozzle travel very quickly in the diagonal direction and you can clearly see the diagonal line with print material on it.

[hyiu0000 0]

Upgraded the Cura to the latest 4.8.0.  Now the diagonal line becomes a horizontal line.  Yes this line does not really affect the print quality that much, but the problem is that when it travel across the print, it scratches the layer with a loud sound.  This seems more like a software bug than a hardware problem.

[hyiu0000 0]

Okay, "Combing mode" is actually enabled by default.  So the problem is fixed by disabling "Combing mode".   But doing so will make the print very slow since it will retract all the time.  Setting the "Retraction Minimum Travel" to a higher value such as 5mm will make it print almost as fast as the default, but of course, now the diagonal line is gone.  So although the problem is fixed by changing this setting, it still does not make sense that filament are spitting out during a travel in "Combing mode".  I think something is wrong with the G-code output from Cura.

[hyiu0000 0]

The print comes out okay, but now I found that the disadvantage is that the print has more stringing, even though it is only a PLA print.  I guess the advantage of "Combing" is to have the stringing stay within the solid area of the print.

 

[hyiu0000 0]

Why does Cura make "Combing" and "Retraction" mutually exclusive options?  Can't they exist at the same time to increase user flexibility?  "Combing" keeps the stringing within the print, but at the same time, I want to use "Z Hop" to avoid scratching the surface, and "Z Hop" must exist with "Retraction".

[hyiu0000 0]

https://github.com/Ultimaker/Cura/issues/5226

https://github.com/Ultimaker/Cura/issues/6470

[hyiu0000 0]

Okay, recalibrate the material flow setting seems to reduce the scratching.  It seems that my previous print might have an over extrusion issue.  So maybe that is what most people do and there is no need to do Z hops.