I've read through past posts about handling power glitches and outages some options seemed a bit complicated to me.

I've come up with a very simple solution to the UPS Backup issue that also takes care of the spindle.

Use a UPS backup to take care of the computer and control box. To prevent the Mach3 from continuing to run if the power goes out and the spindle isn't running I'm going to use a 12V transformer AC/DC converter plugged into a surge protected only outlet on the UPS. The transformer will be hooked to the coil of a normally open relay. The normally open switch of the relay will be in series with the other estop switches. When power is lost the relay will de-energize releasing the switch to open causing a estop in Mach3. To prevent very short power glitches from causing an estop you put a capacitor on the relay coil to hold it up for a brief time after power is lost (the 12V transformer I used has a built in capacitor that holds the relay up for about a second and a half). If power comes back before the capacitor bleeds down then the relay doesn't de-energize. See the attached schematic.

Don't know why I can't show both pictures in one posting.