Vertices that seems to be aligned, are not? Hi all and good to be here. 
I'm new to the forum and fairly new to Blender. I did some tutorials and simple drawings, but now I want to 3D print my designs.

I've created a rim (1/24 meant to be used in scale modeling) 
The inside of the rim containts a 'cylinder' that will be used to attach the wheel to the model car. For some reason, the vertices shown in the image below appear to be somewhat offset when I slice the STL export for printing. However, all the vertices have the same Z value of -11mm.
What am I missing/doing wrong?



According to the slicing tool the outer rim first appears on the third layer, where the center starts on the 1st.


I am aware this could also be a problem from the slicing software... but let's look at the design first.
i had problems like that as well. I ended up just starting from new and being very careful. Blender sometimes just creates some weird slightly invisible vertecies out if nothing. and if u don't ctrl + z them, I don't find any way to get rid of them