"Polymer Man" wrote: (clip)Then come in with a centering drill and drill an
accurately located hole. It will not deflect because it is on the flat.
^^^^^^^^^^^^^^^
Yeah, but OP said he had to drill THROUGH the tubing. Your method will get
the drill started okay, but what happens when it gets to the other tubing
wall from the inside?

I guess he could lay out the "exit point" very accurately and come in from
the other direction using your method.