More thoughts.

A cobalt bit or try a reciprocating saw with a long, fine
tooth, bimetallic blade. If the bimetallic blade won't cut
the screws, get a diamond blade. Just lift the board enough
to get the blade under it and cut off the screws.

Frank

"Martin Noakes" wrote in message
...
Hi all

I'm about to lift an Oak floor that has shrunk in order to
re-lay it after
straightenin the boards.

Here's a picture one of the gaps!
http://www.songcity.co.uk/MyPictures/Floorboards1.jpg

Due to the shrinkage the screws have been bent over and
I'm unable to
unscrew them.

The screws are hardened steel BZP and I wondered if anyone
knew which type
of drill bit I would need to drill the heads off. I have a
couple of
metalwork drills and they don't touch the screw heads.

Or maybe another suggestions/approach for unscrewing them.

Cheers

Martin