Y-dimensions shorter than the x or z - Velleman Vertex K8400

The object that should be printed has not the correct dimensions. In detail, the x- and z-dimensions are correct but the y-side shorter than it should be. So in fact squares become rectangles and circles become badly filled ovals. In the preview of Repetier-Host / CuraEngine it is paradoxically correct. Also the scales are 1:1:1 and we use the standard adjustment from Velleman. The mechanical parts of the printer work good, too.
Can you help me?

If you go to repetier -> Config -> Firmware EEprom configuration

Are the values for steps/mm the same on X and Y axis?

Ja, die Schritte pro mm sind für x und y genau gleich.

// Yes, the steps/mm are exactly the same

Then check if the axis is running freely, especially on the ends of movement range.
Also check if the stepper drivers are set to the correct voltage, (I don’t know the correct value for the vertex, caus i only have a k8200)
to prevent motors from loosing steps.

The machanics work freely and smooth. It seems like cura / repetier has a problem because the printer works quite exactly. The result is exact but short in direction.
Example: On the cura sliced preview the square is correct, but the printer prints an exact rectangle … y-side is 90% as long as the x-side. Curiously the ratio of the Vertex printing space dimensions are also about 9:10 (215mm : 240mm in y and x)… I don’t get that.

This issue can come from a somehow loose motor pulley : Check if it’s not moving a little (you’ll have to remove the motor as you can’t check it when it’s in place).

All mechanical parts work really well as I said before. The software really seems to be the problem. To prevent that the y-side is shorter (in a scale of 1:1:1), I tried 1:1,1:1 … but then the filling-quality is not good (but the shape of the model is correct). If I use 1:1:1 the printing quality is very precise, but one side is shorter

Problem solved. The axis were not exactly in a 90 degree angle, which could be repaired by the little screws.