snafu fired this volley in news:5NqdnfiSF-
:

Can I simply swap the E-stop pin configuration to active low and run
the
axis limit switches normally closed (opening when they are hit?

That's the safer configuration, anyway. That way, if a switch fails (bad
contacts, etc), it shows an unsafe condition.

But you really need to find the source of the noise. Feeding the spindle
AND returning the limit switch signals via STP (shielded twisted-pair)
AND routing them so they aren't in _tight_ physical parallel to one-
another is likely part of the solution.

How's the spindle varied in speed -- variable voltage or PWM? PWM is
quite noisy.

"Loading" the E-stop with some significant current will probably help.
If it took (say) a 50ma swing in loop current to cause a signal change,
rather than a couple of ma would likely help, too.

Lloyd