Comments sought on new build: A CNC Router for RC Gliders and Planes

[Graeme]

I can see a couple off issues with your limit switches (I think). Firstly without your Override switch being pressed, the state of the limit switches is not passed on to the CSMIO due to the relay contacts being open. Also as you are using NC sensors and have all six in parallel the only way for the CSMIO to see a change is if ALL sensors are activated.
I do not know what the enable does to the motor drivers, but as I see it pressing the override switch will either allow the motors to work or stop them. Nothing else can affect the enable. I think you need to look at how you are using the override switch.
I think it might become a little clearer if you view the sensors as switches like in this image

I am not sure if you can achieve what you are trying with NC sensors.
Graeme