Don, the G84 is a tapping cycle code. On the fadal the .1 and .2 and used to signify which gear you want the tapping to be done in. If you are using a higher rpm, the spindle may "coast" to a stop before reversing. The z axis may reverse prior. If you keep it in a lower gear it will respond better. The machine does not know if the tap is chucked rigid or floating. There are physical componets needed to do rigid tap. The proper spindle driver and spindle feed back, not just a tach. Do you have a factory setup sheet in the back of the electrical cabinet? That may tell you. Or you can call the factory with the serial number and they may help you.