• Relay spindle interface - Outputs Max. 36V 7.5A for spindle motors or coolant pump (only one
device can be powered by this output!)

So does this mean it will put out 36v to run the spindle. or just its max input.

It is just a relay but the Gnd has me wondering as I was expecting that to be the common terminal of a NC/NO relay.
What it sounds like is just a normally open relay and you would connect the positive supply to V+ and then V- to your motors positive. The Negative wire from your supply would go direct to the motor. However as said the Gnd has me slightly worried and if I could test myself I would be confident to tell you how to connect but as I cant then it might be best to see if you can ask the supplier of the board.
Hood

No it will not put out 36v, that means it will handle a max of 36v at 7.5 amps through its contacts, you need to supply the voltage for the contacts.
Hood

OK thanks for all the help.

Is there any way I can use this, to index. like a 4th axis?

Don think so unless you have a stand alone 4th axis that reqires a signal to make it index.
It is meant for coolant or spindle on/off like you say and I am almost certain it should be wired like I said two posts ago but as its not mine and I cant test I will not say it is definitely that way as I dont want to be responsible for you letting the smoke out.
Hood