Is there a tap with a pilot bearing?

[UAM fab]

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.

[packrat]

How about a DRAP COMBINATION DRILL & TAP (DRAP) and other DRILLS at MSCDirect.com


cary

[neilw20]

Can you clamp a temporary spoil piece in the gap to equalize the load?

[lerman]

If you can rigid tap, you can probably thread mill. That shouldn't care about the gap.

Ken