Hey Jason,
I’ve looked up what Q3 is in the circuit diagram. The Q2/Q3 and the big white 5.1 Ω resistor are part of a circuit that the TinyAVR on the left of it uses to report the “Shunt Overload” indicator. The TinyAVR talks to the Raspberry Pi via i2c bus.
By the way, I would avoid to let that much wood dust fly around. Before it affects the controller, it certainly will harm your ball screws which are incompatible with wood dust