The message
from Chris Bacon contains these words:

You sure about that? As I understand it, once the compressed outer layer
is broached the whole thing goes bang no matter what. Prince Rupert's
Drops and all that.

I drilled through a toughened windscreen some years ago, which
was OK..... I can however tell you that using a glass cutter is
not a good idea. Amazing how far the bits go.

Hmm. I tried it a couple of times with toughend quarterlights without
success. Laminated's OK, of course.

--
Skipweasel
Pay no attention to that man behind the curtain.