Well there are several options. If your control will do helical interpolation you can do what is called "Thread Milling" where a special cutter is driven in a 360 degree arc in X & Y (the thread diameter) while moving down in Z (the thread pitch) The nice thing about this method is you can mill just about any size or pitch thread, inside or outside.
Some controls also have "canned" thread cycles where the tap is heald in a special chuck and the control sends it down to a certain depth then automatically reverses. The tap holder usaually has some "float" in Z to take up for the difference in reversal time from the axis drive and spindle drive.
Do not try to machine tap with standard taps. Machine taps are designed to either pull the chips out (blind hole) or drive the chip down (through hole)
Mike |