Removing the bent screw from a piano leg might be a difficult job,
requiring grinding the head off or drilling a small hole in the slot and
progressively drilling larger and larger holes until the head falls off.

It is very difficult to center a drill bit in the head of a screw with a
slot in it.  The drill wants to run to the outside of the head, and this
is not where the hole needs to be.

However, it is my experience that about .001% of the population owns all
of the good screwdrivers.  I have plenty myself but am constantly amazed
at what others (including some excellent craftspeople) seem to think a
screwdriver should be!

There is a tremendous difference between a good quality screwdriver and
a bad one, and there is exactly one that is suited to each type and size
of screw.  Even a good screwdriver that is too small will not work, or
worse, it will damage the screw.

For a slotted screw, the tip of the screwdriver should be as big as will
fit in the slot fully inserted and the tip must be hollow ground, not
tapered as the cheap ones are.  This tip will pull itself into the screw
instead of pushing itself out like the tapered cheapy.  The steel of the
screwdriver should be hard enough to not bend, but also not so hard that
it breaks.

The reason I am mentioning all this basic screwdriver information is
that it is quite likely that the screw can be removed or broken off with
just a good screwdriver.  It might need a good screwdriver bit in a
ratchet handle if it is really tough.

Most of the time a screw bends in the threaded portion and this is the
weak area and weakened more by the bending.  If it does not come out it
is likely to break there and allow the parts to come apart.  If the tip
is the right size and of good quality and the head is not already ruined
there is a very good chance it will come out or break.

If the screw is badly bent, make sure you change the angle of the
screwdriver as the angle of the head changes and take all the other
screws out first to allow the parts to move as the bent screw moves them
out of their correct position.  If it breaks you can dig out the rest in
an area that will never be seen, or drill a new pilot hole at a slight
angle to hit wood to the side of the old embedded screw if there is
room.

If the stub must be removed, there are tools made to do this by drilling
around the screw.  You then need to glue in a plug to fill the oversized
hole, or better yet, install a machine screw insert and use a machine
screw or bolt.  I have seen very few good screwdrivers in the hands of
anyone other than the most fastidious mechanics and technicians.  I doubt
that the mover had a screwdriver that was good enough to remove a large
bent screw.

Here is one last possibility, but I would make sure to be very careful
where you are prying on the wood so as to not damage anything that will
show, and also be sure to not force anything to the point of breaking.

If the leg is installed in such a way that removing all the other screws
allows you to insert a wedge, you might be able to use the leg as a lever
(or a pry bar inserted into the gap) against the wedge to straighten the
bent screw enough that it makes it easier to remove.  Pay careful
attention to the direction of the grain of the leg components and stop
levering if you feel or hear any wood or glue joints cracking.

Spencer Chase
http://www.SpencersErolls.com/