How do I control the single line width in Prusa Slicer?

Maker Talk
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I’m needing to control what Prusa will resolve as a single line. By nature, it cannot be less than nozzle dia, and things do tend to go wonky when asked to do like 2x. But otherwise it works brilliantly and produces structure you can’t get any other way. Also can be a trick to produce exceptional layer adhesion, abeit at the loss of bridging.

I got Cura to do it. I can’t find the setting in Slicer though.

Basically:

  1. I have a 0.4mm nozzle. My design has a thin 0.4mm wall and a 0.6mm wall. No solid to infill, just a single wall, but it CANNOT be vase mode as there are other features on that layer that cannot be a single path It needs to extride the 0.4mm as one line only, and 0.6mm as one line only by extruding 50% more at the same Z-step. If the feature is a very acute triangle that widens past 0.6mm and then pas 0.8mm, this does present a problem, it might be best to start at 0.4mm, extrude extra to get 0.6mm, then go ahead and extrude past 150% until it hits 200% then start rending as two 0.4mm lines when it’s 0.8mm or wider.
  2. I have a horizontal trapezoid with a 0.4mm top surface and another with 0.6mm, and variable layers. Needs to give the same single-line result.
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A diagram/cross section of the desired part would help me visualize this.

Suppose it would also help if you describe what you did to get Cura to do it, might give us some more clues to work with.