Partial infill taking longer than full infill?

[Brandis 0]

Want to print this model https://www.thingiverse.com/thing:4013242 and the maker recommends on only use infill in the bottom and the top. Using Cura 4.7.0.

 

Then I create an eraser cube, size it so everything execpt the bottom where I do want to have infill is covered, then change the setting eraser cube to "Mesh Type: Modify settings for overlaps" and "infill mesh only" and finally "Infill density: 0%"

 

When I slice it, in the preview it looks ok, only bottom has infills but not the walls. However, printtime and material usage is much more than if I have infill everywhere.

 

Why is that?

[GregValiant 48]

I used LB_SPIRAL_BOT to check.

Model rotated so the bottom is down

Eraser size = 100,100,100

Eraser location = 0,0,3

Eraser cube settings - Wall Thickness = 0 and Top Bottom Thickness = 0, and Infill Density = 0.

My settings were .2 layer and .2 initial layer.  I got 7:46 print time and 23.85 meters.

Without the eraser and at 10% infill it was 8:33 print time and 28.35 meters.

 

If you "remove" the Wall and Top/Bottom settings from the eraser - it will go to the "Infill Mesh Only" default and add additional walls inside the regular walls.  That might be where the confusion is because that does add material.

 

That's an interesting box.  I might print one up.