I am tapping a hole in an aluminum extrusion on a cnc using a rigid tapping setup. The problem is the the pilot hole is not a complete 360. The hole is only 3/4 round and the tap is having a tendency to work its way towards the opening. The tap is an M16 going to 3.25" deep. I was wondering if the tap had a pilot if that would keep the tap concentric with the axis of the hole.