I never thought that calibrating would be such an adventure, but at least I've been finding a lot of interesting things I had no ideia until now.
I've learned more about how to tune the firmware, to calculate the values to insert on the DEFAULT_AXIS_STEPS_PER_UNIT variable on the firmware.
Now, after finding that somehow I was unable to communicate via USB to the printer I had to find solutions for this problem, so I could flash my custom firmware. In the while I've found this Repetier software and with it I was able to connect again to the printer. I'm liking it because it has a lot controls, graphics and informations that I didn't hat with Cura or slic3r.
I've printed directly from the PC a new cube and the results were not yet perfect but almost. The X and y had only 0,2mm difference and the Z was on the spot.
I'm printing now the Lock_CornerF2 and I'm hoping that it can fit right away. LAst night I printed it with Cura and as predicted it didn't fit. Let's see now if this repetier is the silver bullet... :)