I have issues with tapping depth. it's always vary anything between .50mm to 2.0mm.. (I know it's weird..).
Rest of the operations (drilling,milling.etc.) are fine!!!!
Machine Type: Galaxy CNC Milling
Controller : Centroid
OS : Windows
Sounds like a centroid acorn question go to their forum im sure someone there will help . You can try adding a number value after the z-5. Try something like z-5.001 this way the motor will have to dial in closer to the given number this helps with industrial cnc machines im not sure about centroid