Cura line size vs object size

[CasaDelGato 1]

If I'm printing a piece that is 5mm wide, and using a 0.4mm nozzle and line width.
How wide is the resulting object?  is it 0.2mm larger or smaller than designed?  or does Cura do some trick to make it the correct size?

 

[burtoogle 509]

Cura does lots of "tricks" but in this regard it is straightforward. The outer walls will be inset 1/2 of the line width from the outline of the object so, in theory, the object should have the correct outer dimensions. Of course, that assumes that the printer motion is perfect and the extruder calibrated, etc. so, in reality, it is normal for the object to come out slightly the wrong size and some tweaking may be necessary. This is FFF printing, after all.

[CasaDelGato 1]

So, for a solid object (no infill), it must underflow at some point?
a 5mm wide object, using a 0.4mm nozzle, is 12.5 nozzles wide.  If I have the walls set to 7 lines wide.  what happens?

[burtoogle 509]

It only generates sufficient walls to fill the space. Unfortunately, at the present time, Cura doesn't handle the situation where there is not space for an even number of walls very well. This defect is well known and the UM devs are currently beavering away night and day to come up with a solution.