Well done sir.. Salute.

only thing I can suggest, is, instead of driving each shoulder of the gantry with its own stepper motor, connect the two ballscrews with a long belt to one stepper. you wont regret it. That way you can calibrate it square once, and it remains mechanically fixed that way going forward.

I think a few of the boys have done it, most recently mr njhussey look at his thread

matt