SOLVED:
Just finished one simple print and everything looks working fine.
first problem:
I've just inverted the extruder connector on the Arduino shield
second problem:
I've used the simple procedure explained in this tutorial from Ian Johnson:
[
www.youtube.com]
The only big difference is that the last value in the string #define DEFAULT_AXIS_STEP_PER_UNIT was much greater than the new one (around 600 while the new value after doing some calculations is only 95).
Suggestion:if you move from a geared extruder to a direct one during the first calibration take away the bowden tube and allow the filament to come out freely since the first time you're gonna extrude something between 500/600 mm so pay attention!
Cheers
Albert