Problems Tolerance

[Didi]

Hi all guys, I've been going crazy with my CNC for 3 days and I don't know where to turn my head anymore.
It is self-built in 25mm ergal, very stable.
I spent a day calibrating it after the move and it's perfectly calibrated,
I also redid all the stepper calibrations with centesimal precision on all axes (calibrated with Mitutoyo comparator)
Now the problem arises, if I tell it to move 20mm via MDI it moves 20.00mm, very precise on all axes.
If instead I make him make a 20x20mm test square directly from the post processor file, he makes it 20.2 x 20.2mm on both X and Y, tested at any speed, it doesn't change.
I use CAM fusion360 (non-hobbyist) and UCCNC post processor with UC100.
Tried the kernel at both 25, 50 and 100...it doesn't change.
Checked backlash, and adjusted on x-axis.
It gives me the impression as if in the passage between the fusion file that I download onto a flash drive, and the CNC's PC, something happened that generates the error.
Can anyone help me?
Thank you

[ger21]

If you are cutting a 20mm square, and measuring it, try cutting in the opposite direction. The most likely answer is that you are seeing some deflection. Also verify the actual tool diameter.

[Didi]

Thanks for the reply, the diameter of the tool is correct and I think that if I had a deflection it should cut the square narrower and not wider, is that correct?

[Didi]

SOLVED... so guys, everything you wrote to me is absolutely correct and I had already checked, the only thing I hadn't tried to do was try the contour from concordant to discordant and everything went perfect... I know this It's important but I hadn't thought about it much.
I ran the tests with 3mm carbon fiber, 1.45 cutter, 700mm/m feed, and 3.5mm depth in one pass.
Thanks everyone for the help.