On Fri, 04 Sep 2009 23:47:02 +0100, Dave Plowman (News) wrote:

... is it possible that the bit deflected inside the wall?

Possible - but then the pipe would bend as easily.

15mm tube is far more ridged than a 16mm drill. The drill is also far
more likely to drill a hole with a kink in it(*) rather than a smooth
and even bend. A hole with a kink requires the bend in the tube to
move along the tube as you (try to) put it through the hole.

You'll get away with a small deflection but not much more than a few
mm in every 300 or so.

--
Cheers
Dave.