Yes, you can use a corner plate very easily. You will want to make a corner plate that has three independent plates that do not conduct with each other. Each of these plates will be connected to a different input (i.e. IN1 for X, IN2 for Y and IN3 for Z). The end mill or tool that is inserted into the spindle will connect to V- of the 24V power supply, or the DCM on the controller, which is connected to the 24V V-. Then, you can use the ref all home button on the program run screen of Mach3.
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 Is there a way to use an X,Y plate that will only be responsible for corner finding?