Problem solved! I found 2 lose screws at the back of the gantry 🙂

Thanks for your reply, but I don't think this has anything to do with backlash. I'm using a pen at very low speed. I did a new test, I combined a circ...

I see that the system here rotated my image 90deg. So the straight line is de Y-axis, not de X-axis! And I did one more test, quick engraving, but...