Skirt extrusion width does not account for second extruder nozzle diameter

[simonkuehling]

When doing a skirt with dual extrusion all skirt loops are printed with the same flow rate for both extruders (standard extrusion width of first extruder is used).
Using two nozzles of quite different diameter for the extruders (here: 0.35mm on extruder #1, 0.75mm on extruder #2) this results in the second extruder trying to print skirt loops as thin as the first extruder - but doing a 0.39mm extrusion width by a 0.75mm nozzle just won't work :-)

[alranel]

I confirm that, Simon.

[simonkuehling]

I also noticed today, that with two extruders and 5 skirt loops the generated gcode will first print two loops with extruder No.1, then two loops with extruder No.2 and then another loop with extruder No.1.

Is this sequence intended by a specific reason?

[alranel]

No @simonkuehling, the order does not make sense and I need to change it :)

[lordofhyphens]

This is partially addressed by #3349 @simonkuehling is that enough or did @alexrj fix it before then?

[simonkuehling]

As of 49f327f in the stable branch, this issue still exists - i just checked that quickly. Due to the fact that a dedicated skirt width always applies to all extruders, an extrusion width of 0.5mm will not work with a 0.35+0.75mm nozzle dual extruder setup. The most obvious workaround to just use 0.75mm skirt width instead may get problematic for the smaller nozzle pretty fast as well.

There are other strategies to prime two extruders than using a skirt, of course. We do the priming in front of the printbed (extruding freely and then sticking it onto the print bed edge) from the start-gcode ever since.

So, while potentially a cause of failure, this issue has no priority i think.
We should include a warning, though - just telling the user if the skirt extrusion width is too low for one of the nozzles configured.

[lordofhyphens]

When you have some time, could you take a look at the PR for skirt width
and see if that makes anything worse?
On Jun 3, 2016 5:27 AM, "simonkuehling" notifications@github.com wrote:

As of 49f327f
49f327f
in the stable branch, this issue still exists - i just checked that
quickly. Due to the fact that a dedicated skirt width always applies to all
extruders, an extrusion width of 0.5mm will not work with a 0.35+0.75mm
nozzle dual extruder setup. The most obvious workaround to just use 0.75mm
skirt width instead may get problematic for the smaller nozzle pretty fast
as well.

There are other strategies to prime two extruders than using a skirt, of
course. We do the priming in front of the printbed (extruding freely and
then sticking it onto the print bed edge) from the start-gcode ever since.

So, while potentially a cause of failure, this issue has no priority i
think.
We should include a warning, though - just telling the user if the skirt
extrusion width is too low for one of the nozzles configured.

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