I have a Warco WM16 milling machine that I'm converting to CNC. The machine is now protected with "end of travel" limit switches - these are N.C. contacts in series with the E-Stops, so provide safety by dropping out a contactor which controls the mains supplies.

I'm now looking at fitting of homing switches but am not sure where "home" will be as it's not really a constant. I also need to setup the software to account for the machine limits. For instance, for 180mm of travel, do we set the software limits to 0 to 180, -90 to +90, or some other value? Obviously this also affects how the homing switches will work. I'm guessing that the X and Y axis will probably home to the centre of travel and the Z to the top of its travel?

So my question is: what is the "conventional" setup for milling machine home positions and switches?