Single outline prints two passes

[zemlin]

Factory file is attached.
I printed this part with a .25mm nozzle wanting the vertical wall to print .3mm thick. It looks perfect on the preview (had to back the extrusion diameter down to .29 to remove the gaps), but when printing the nozzle makes two passes on each layer resulting in too much plastic per layer and a wall thickness of .5mm.

Why would the wall that's shown as one layer print two passes?

[jimc]

S3d will put a single extrusion on each surface of the model. The wall has 2 surfaces. You cannot print a single extrusion wall. Depending on your overlap and thin wall settings s3d will try to squeeze them together to get you a bit narrower than 2x your extrusion width but then you end up a little over extruded.

[zemlin]

You cannot print a single extrusion wall.

What would be the benefit of this limitation?

In the Thin Wall feature request thread there's a lot of sentiment about S3D not compromising accuracy in order to lay down material that shouldn't be there, yet that's exactly what's happening here.

[jimc]

yes thats why its a user selectable feature. its the thin wall behavior settings. thats the amount of allowable overlap. its not a perfect solution. its about a 1/2 way between. you can generally handle about 15-20% overlap and still keep things in spec but if you wanted more you can set it that way. depending on the model the overextrusion may not matter and it would be better to have the over extrusion than s3d not print the feature all together so that is why they added the thin wall setting.