The answer to your question should be in the Mach 2 instructions. I will leave the details to others with experience on this software.Originally Posted by ironDigit
The controllers do not know the length of any bit in the spindle. You set Z zero to the end of each tool along with the diameter in a tool offset or library that the control will use to compensate motion via the actual path programmed.
The true length of the cutter needs to be considered by the programmer and operator to prevent either programming a depth beyond the tools capacity or the operator selecting a tool shorter than the depth expected for that operation. Thereby making the human interface the de-fact-o brains of the system to prevent conflicts in the machining envelope. That includes chuck diameters, clamps or anything in the path that one would not want a cutter, holder or otherwise to pass through unintentionally.
This type of question is a great reason for dry running a program to verify all is as expected before unleashing the "unknown" onto an unsuspecting machine in your trust. Precisely why there is a feedhold and E-stop on the machine. Stuff happens!