Thanks for the replies.
I think I finally wrapped my head around this. I'm a nuts and bolts guy so sometimes its difficult to visualize the electrical connections.
The relay on the breakout board is a pass-through switch with NO, COM and NC connections. So in my case I will be using DC to AC solid state relays (SSR) to toggle the device on/off. All that needs to be done is run one leg of the low volt circuit through the BOB relay NO & COM and set the the appropriate output pin in Mach3 (pin 14 for this board set to active high). When the BOB powers up the relay will be open (NO) so nothing will start. When the input in Mach3 is toggled it goes "high" closing the BOB relay and completing the circuit to the SSR.
The "B" axis is not being used for a motor so the Step (pin 16) and Dir (pin 17) are available as outputs. Again using an SSR, the DC (-) side of the relay is wired to GND and the (+) side of the relay goes to pin 16 or 17. When activated (high) by Mach3 the pin applies 5v and activates the SSR.
I confirmed the wiring with a multi-meter and then tested each with a SSR wired to a flood light. Works!!!
My mill finally be delivered tomorrow (YAY!!!) so I will be able to see how the spindle motor is switched so I may have more questions about integrating that.
bloomingtonmike - thanks for the help. Currently the mill is just on/off, no VFD. That may come later.
jumps4 - A buddy gave me a dozen SSR-25DAs with heat sinks. I think these should work okay.
Jay