"wingnut" wrote in message
...

Why are you doing this?

To provide heat and AC to a basement. The basement currently has supply and
return ducts running across the ceiling, but there are no supply vents or
return vents.

I just did the tin snips routine today and it worked without too much
trouble. I also did what someone else here suggested and folded back a tab
of the sheet metal on each end to create a double thickness and make the
opening more rigid. That worked well too.