[Dimensional accuracy problem with holes]

Hi,

I'm having problems to print separate parts which should fit together. So I created a test print.

I have a cube with the dimensions of 20x20x10mm

I subtract another cube with 10x10x10mm from it so I get a hole of 10x10mm in the middle of the first cube.

 

When I print this with my Ultimaker 3 all dimensions are perfect except the hole in the middle. It is 0.5mm to small in both dimensions (x/y).

 

I found the "Horizontal Expansion" parameter in Cura which allows me to correct this but this affects my outer dimensions as well.

I tried various materials (PLA, ABS, InnoFlex Pro1) and got the same results.

 

Does anyone have an explanation for this behavior? 

Any suggestions how can I avoid this?