Size correctness of a print?

Vertex 3D Printer Vertex - Issues while printing
1

When i print a ring
outside 40mm inside 20mm
it prints the outside spot on 40mm, inside is printed to small 19.5mm

What could be the reason for this? Somwhere a wrong setting in cura?

2

It’s a well known slicer issue, not so easy to get rid of.

Read some explanations about it [color=#408040]here[/color].

3

[quote=“raby”]It’s a well known slicer issue, not so easy to get rid of.

Read some explanations about it [color=#408040]here[/color].[/quote]

Thanks Raby