Xy gap too

My printer has a variation of about 4% lower on the X axis than Y axis. I have printed several calibration pieces and allways same thing.

The belts are taut , tight engines and i don´t know what else to do. The rods are perpendicular , almost no sound . The print quality is very good in art pieces,

The main problem is to make pieces to attach with screws and nuts or include rods or bearings. Using PLA now , although with ABS the same variation occurs .

How could solve the gap ?

Thank you very much everyone