Hi,
I got the same as you. That will get you in the ball park. You will then have to calibrate or fine tune each axis using the axis calibration in mach3
No, the calculation should be perfect. There should be no need to tweak it, if you do then that means that you are doing something wrong or the stepper is missing steps.
It is nice to think that microsteppeing improves resolution, but it does not work out that way in practice. There is a rather long a tedious explanation as to why that is case,
it all comes down to diminishing torque between microsteps. In truth most steppers can do no better than half-stepping, ie 400 step/rev.
The principle gain with micro stepping is not resolution but motion smoothness. Astronomers first invented microstepping with steppers mainly to smooth the movement
of their telescopes. At around 8 microstepps per full step is a good compromise. You get the majority of the smoothing that is available, whatever resolution gain you can get
without overly increasing the signalling rate. I would suggest changing your driver switches to either 8, or 10, or 16 microsteps per full step.
The manner of the calculation remains the same.
Craig