I am having an issue with a clients small mill.

When I try and home the Z axis, Z goes up for a bit sometimes it hits the switch, sometimes it does not.  Then it reverses direction and starts going down.  Indefinitely.

If I home Z and manually trigger the switch, it will work.  So first I though of debounce settings.  I got up to 50 in the smooth stepper config and 100 in each of the debounce settings in general config in mach 3.  None of these seem to have any effect.   

Y and X seem to home just fine.  Z axis is the one with the issue.  If I manually push the switch, I get the Z axis home LED light.

Anyone have any ideas?

The debounce setting in Mach have no effect when using a SmoothStepper.

It sure sounds like switch noise to me. Can you swap the switch out with another one? Also keep in mind that the noise filtering values you enter in the SS config are in microseconds. Entering 2000 gives you 2 milliseconds, etc.