Ok, its working however at startup the boards 'click'. It did not cause a problem at first but now the coolant pump starts / stops as the relays change state.

Any idea what can be causing this? I tried a different 5V supply. I believe the 24V supply can offer enough current. I cant see any voltage drop as such.

Could it be Mach 3 initalising as the PC boots up? Not sure if I can create some form of 'dont power anything till everything is ready' steady state. The PC currently is fed from the same power as the CNC. Perhaps I should power the PC on its own and see if this still happens during the machine start up.

Once everything has been booted and settled, the clicking goes away.