Accuracy: Extrusion width and/or Extrusion Spacing

[Lodran]

Add "Extrusion width:" and "Extrusion spacing:" to the accuracy panel, as advanced options.

The two would be tied to each other, with changes to one being reflected in the other.

If I had to choose between one or the other, I'd rather see extrusion spacing.

In skeinforge, Extrusion spacing = Extrusion width / 1.272.

Note: When printing a 2mm wide rectangle with an extrusion spacing of 1/3mm (or extrusion width of .424), and 2 extra shells, Skeinforge lays down exactly 6 filaments, with equal spacing between them. This implies that the finished part will be about 1/10mm wider than expected, which could explain a small part of the issues we have with hole diameter in skeinforge.

[alranel]

Okay, it's there. --extrusion-width-ratio allows to specify the extrusion width as a ratio over layer height. When left undefined, Slic3r calculates an optimal width automatically. Having an explicit width setting in mm is just a GUI issue, so it will be there soon.

[Lodran]

I have to say - extrusion width as a ratio based on layer height doesn't make any sense at all, particularly if you're experimenting with different layer heights.

If it has to be expressed as a ratio, it should be based on nozzle width. Ideally, it should not be expressed as a ratio at all, because when you are tweaking extrusion width, it is usually because you are trying to fit an exact number of perimeters into a small space.

[alranel]

Just a note. Extrusion width expressed as a ratio over layer height is a shape factor of the extrudate. It does indeed make sense. The shape factor changes the strenghtness of the printed part. For details about it, see the upcoming book by Josef Prusa :)