trying to understand nozzle size relating to model dimensions

Hey all,
first post and trying to solve an annoying phenomenon.
I've been making my models in CAD, sending them to Cura 4 and the slicer is under-sizing my vertical wall thicknesses. I draw a 2 mm wall, Cura draws them thinner. I'm guessing it has to do with the nozzle diameter multiplier (.4 mm) and maybe some settings somewhere. At .4 mm it specifies a wall thickness of .8 mm, and I guess multiples thereof. If that is the case, what can I do to reliably work at half mm width values eg. 0.5, 1, 1.5, 2 and so-on?
Would a .5 mm nozzle work better for this or am I barking up the wrong tree? I'm making functional engineering models so the walls, ribs, pillars, screw hole walls need to be the specified thickness or it ends up useless. I tried 'thin walls' to see if that helped, not so much. If anyone has any advice I'd be very grateful.
Cheers

get simplify 3d :-)

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Originally Posted by curious aardvark

get simplify 3d :-)

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No money for that, gotta work with the free stuff.I did find out that it is a problem with something Cura is doing. I can refresh the profile and it looks fine, start it up later and it's all gone to crap again. At least I know it *can* work properly. I think I'll try an older version, see if that'll be any more reliable.

I Have some Cura 4 Profiles which may help you.

You could install them then configure your own 3D Printer specifications.

I use Cura 15.04.6 more than the newer Cura versions because it is simpler to use.
Only use Cura 4 when special features are needed for printing a 3D Model.

thanks!
There seems to be one setting which is throwing it off but I haven't nailed it down yet. I think it might be horizontal expansion that I like to run at - 0.4mm. More testing to go but getting closer.

In S3D there are many things that can change your wall thinkness.

You set your Nozzle diameter which is used in calculations, you set your Extrude width which is the thickness you want the extrusion to be. rule of thumb is 1.2x nozzle size. I like .5 for .5 nozzle with my printer. Then other settings that do other things will screw that up.. If the starting height is too low it can cause the wall to be fatter. If the extrusion multiplier is too low walls will be under sized, to high then they are too fat. If the filament diameter setting is set to 1.75 but the filament is actually 1.69 or 1.71 then your expected extrusion will be under extruded and wall too thin. Not sure how cura works but they both do the same thing.. change stl to gcode.. Good luck!

in simplify3d there are also settings for single line walls, wall infill settings, and all very easy to find and adjust.

One thing to check on cura is that it hasn't changed from 1.75mm filament back to 2.85. Apparently this is something it likes to do.
Cura is an ultimaker piece of software and ultimaker only use 2.85mm filament.