Limits, homes, override switch

[paulus.v]

The most economical way is to have one microswitch and one inductive sensor per axis fitted on the moving part. And you mount them so that they pass by their respective adjustable metal stops on both ends.
Then you wire the sensors in parallel to one BoB input (or to separate inputs if you have them, and you can home all axis simultaneously) and the microswitches in series with the e-stop. You put the limit override to bypass the microswitches loop but not your e-stop.

In normal operation you will be using only the sensors and only for homing. You will have to set in mach3 the soft limits which will prevent you to hit the limit sensors. In the case you hit the limit sensors you tick in mach3 the automatic limit override and manually back off the respective sensor. Normally the miocroswitches will never be used, only in the worst case scenario if the software is no longer responding or the motor drives are failing, etc., then hitting the microswitch will cut the power to both motors power supply and spindle.

It is better to have both switches and sensors to operate at 24V. If your BoB do not accept 24V you can either use an optocoupler with a resistor or if the BoB inputs are optoisolated you may change the value of the resistor on the board.

I noticed you have fuses on your power supplies inputs. You want to have fuses on the outputs to actually protect the power supplies for short circuit, etc. The mains will be protected with one or more circuit beakers. (Eg. one for spindle+motors PSU and one for the 5V+24V PSU)

Edit: you will also want to wire the alarm outputs from your drive through a relay to the same limits + e-stop relay loop. In this case if one drive gives an error, the other will stop as well. It is also good to have the BoB e-stop input better connected to a mach3 input. This way you can tell mach3 to stop the g-code if the motor power switches off. So you can resume your job quickly.