Thanks for the encouragement Geoffrey!
Got the latching bit working on the master relay so it stays on when reset and trips out on estop button being pressed.
Got power to the first 2 drivers via the relays so starting to come together.

Very pleased that it is working as per my original electrical plan. One thing that bothers me is that if I power up the spindle manually and there is an estop then the inhibit relay will tell the VFD to stop. All good except when I reset the fault the spindle will come on straight away. something for me to watch if I use it manually

Most of the time the spindle on/off will be under mach3 control and I'm expecting the relay on the BOB to trip if there is an estop so no problem. Does anyone know if the Bob will trip the spindle relay if there is an estop?