Ok, very slow. I think you can overcome that issue by tweaking the homing routine, but my latest CNC creation isn't quite complete enough to test that.
I think a routine like this would work:
move at 10% speed in the home direction
stop when you see the home/index signal go by
backup at .1% speed and stop when the home/index signal is active
Your home position would have to be a little off the physical limits to allow for a bit of overshoot, but that's good practice anyway. The commercial CNCs I've worked on have a seperate decel switch to indicate when to slow down and then use the limit/index combo for homing. You could do the same with Mach if you tweak it I think.
Pete C.