Rectract Before Outer Wall not working - ZScar issues

[amagro 1]

Hi,

I'm having some issues with the zscar, I already try most of the possible combinations with Cura settings and I am continuing having problems as we can see in the image below.

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I think the main problem that is causing the issue in the image, is the lack of pressure inside the extruder when it starts extruding the outer wall. Before the outer wall, the extruder does a long travel move, and during this travel move some pressure (filament) goes way from the extruder.

Also this long travel move is strange since the the "Z Seam Aligment" is "Shortest".

After analysing the gcode, I found that the "Rectract Before Outer Wall" setting is not working as we can see in the next image.

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What I intent with this setting is to hold the pressure inside the extruder soon after the last extruder path (in the below layer), and then ensure that when it starts extruding (on the next layer) it will not have underextruding issues.

I also found that if the "Retract at Layer Change" is activated the rectration will occur in the same x y position where the outter perimeter will start, this situation contributed again for the loose of the pressure in the extruder.

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This two settings "Retract at Layer Change" and "Rectract Before Outer Wall" in order to be more eficiente must happens on the end of the last extruder path (yellow arrowhead in the gcode images).

Cura 2.7.0

Tks

Edited September 22, 2017 by Guest

[amagro 1]

It seems that the "Rectract Before Outer Wall" sometimes is made.

[smartavionics 157]

Could please post a link to the gcode so I can have nose around, thanks.

[amagro 1]

https://www.dropbox.com/s/r1l4rqbigvdlzks/3DBenchy.gcode?dl=0

[smartavionics 157]

Thanks for the gcode - I've found the bug (it's not one of mine!), it's triggered by the combination of retract before outer wall and outer wall printed before inner walls both being enabled and the end of one layer being some distance away from the start of the new layer. I will submit a PR that should fix the problem to the Cura devs.

[smartavionics 157]

PR raised, see https://github.com/Ultimaker/CuraEngine/pull/610

[amagro 1]

Really appreciated @smartavionics

[ghostkeeper 66]

And it's merged. Thanks for the debugging, guys.

[amagro 1]

Hi @ghostkeeper,

The issue with the "Retract at Layer Change" that is happeing in the same x y position where the outter perimeter will start (that contribute for the loose of the pressure in the extruder) was not solved, only the "Rectract Before Outer Wall" was corrected.

As you can see in the image, after the last extrusion (and here is where the retraction must occour) there's a long travel move, then a retraction happens, goes to new layer and prime, all this on the exact same place.

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[amagro 1]

Here's the gcode: https://www.dropbox.com/s/z6dqigty8etkdqk/3DBenchy_print2.gcode?dl=0

[smartavionics 157]

Hmm, I thought that was sorted, obviously not. Let's take another look at that...

[smartavionics 157]

Just doing a quick test and it's working for me. This image shows the retracted travel move (yellow) to the start of the outer wall. Will continue to investigate.

[smartavionics 157]

Edit - no, I was wrong it's actually working OK (duhh, I forgot to turn on the retract before outer wall setting!) So at the moment, it's working OK for me.

Edited November 9, 2017 by Guest

[smartavionics 157]

And, guess what? You made the same mistake! In your gcode file it has the evidence:

travel_retract_before_outer_wall = False

[amagro 1]

In this gcode I was not using the "Retract before_outer_wall" option (but I know that it's already working), I was testing only the "Retract at Layer Change".

Edited November 9, 2017 by Guest

[smartavionics 157]

Ah, sorry, I misunderstood (should have read your posting more carefully!)

[smartavionics 157]

I have modified the mod we made earlier to take into account the retract at layer change setting. A quick test appears to do the right thing so I will create a PR and then the Cura devs can decide whether to incorporate it or do something different.

[smartavionics 157]

See https://github.com/Ultimaker/CuraEngine/pull/650