Curaengine - Spiralize problem

What is the number of perimeters you have chosen? Are wall thickness depending on slicer. The wall thickness can only be an even multiple of your nozzle width to get proper infill.

You also cant print a 2mm wall with a .8 shell thickness. You cant get 2mm by multiplying a .8 shell. Try changing to a .5 shell.

Correct. The reason is the printer csn control the layer height based on the movement of the z axis. But the only way to control wall thickness is your flow rate which is static and some fuzzy math between your nozzle diameter and the layer thickness. A .3mm layer thickness should yield around a .48mm thick wall on a properly calibrated machine. A .2mm layer will follow the same math.

Yes flowrate can be changed but during the print it remains at that setting unless you change it or the gcode changes it.

So in a nut shell you want to design your walls so can be evenly divided by your nozzle diameter or you may find gaps where the extrusion may not meet the previous wall, or when doing solid infill the infill may not make full contact with the wall.

The way it was explained to me is you first want to run a test. To do this print a single wall cube with no infill. This way you just get a cube with one perimeter. There are some you can download on Thingiverse. print that with a .3mm layer thickness. What this will do is tell you what your actual print width is. Once you know this then you can figure out how many perimeter you can allow in a models wall and such.

Lets say you want to print a cup with a 3mm wall. Lets say you find out your print width for a .3mm layer is .40mm just hypothetical numbers here. What you would want to do is divide the cups wall thickness (3mm) by the known perimeter value (.4mm). You could make the cups wall with 7.5 perimeters of course you can't print a half perimeter so you can't make the wall with all perimeters. So what we would do is use 3 perimeters. That will put 3 on the outside and three on the inside and then the slicer would infill the space between which would be .6mm which may or may not fill to the edges since .6 won't really divide by .4. Yo may have a .2mm gap between the infill and the perimeters and again you may not.

But you get an idea of how the math works.

I would also not use the spiral function on anything but round objects with single perimeter walls such as a vase. It is supposed to make a continuous extrusion but can't because you are not printing a round object and your object has multiple perimeters..

If you hover your mouse over the various settings there should be a tooltip that pops up and explains what the function does and what it would normally be for.

I assume you are using Rep Host. If so, dont use the cura slicer initially. Use the Slic3r engine to confirm your machine first. You will understand why once you start setting it up. As for cura, get the actual cura host and use it. Much easier to deal with and fully integrated with cura slicer.