Using shielded wire for limit switches

Question 1-Will this allow me to have both hard and soft limiting…?

Question 2-Should the shield be connected to ground at both ends or only one…?

I would guess only one, otherwise you will generate a ground loop, always have one way for the ground to go.

in the absence of shielded cable would twisted wire help? Back in the good old days of radio control models we used twisted wires on long runs to help eliminate interference.

I am by no means an electrical engineer but understand the concepts, just curious if someone more knowledgeable could chime in

The wire that the X-Carve comes with for limit switches is twisted, and was susceptible to noise when I enabled the hard limits and then started up my spindle. Hopefully just the shielded wire will suffice, it may require some additional filtering (like a small capacitor) if the hard limits are still getting false positives.

So, with that said, should the shield be grounded on both ends, or just one…?

Always only ground at one end.

For limit wiring, regardless of wire type or length, I always add a 0.1 ceramic capacitor from the limit input pin to ground. It is good, cheap insurance against false limit triggering.
John Champlain

Switching from normally open to normally closed is more noise immune too. Normally open is held high using the internal Arduino pull up. That is about 30k Ohm as I recall. Normally closed would leave the circuit hard connected to ground in the normal run state. You could add an additional, external pull up to the normally open style.

This requires setting changes to grbl and a recompile.