Hi,
the mm/inch button you refer to is equivalent to a G20/G21 command which directs the Gcode
interpreter that the current Gcode/MDI is in either mm or inches.
What you are looking for is called the native units. Config/SelectNativeUnits, see attached.
At the moment your native units, these units are those the Mach uses to calculate motor tuning, homing, limits etc
are mm's. Once you set them LEAVE them alone. That does not mean your machine is limited to mm (or inches),
thats what the button or G20/g21 are for.
So at the moment your 'StepsPerUnit'=400 and
'MaxVelocity'=3200
MaxPulse rate= 400x 3200
=1,280,000 pulses per minute
1280000/60 =21.3333 kHz
Thus if you leave the kernel speed at the minimum 25kHz default Machs parallel port is still fast enough for your motor
tuning.
Craig