I seldom use plywood for anything -- and fir plywood for absolutely
nothing in player work.

You would find a lot of poplar plywood in player components, from the
bottom boards of the Duo-Art expression boxes, to the pumps and
reservoirs of upright player pianos.  You would never find lumber yard
quality fir plywood in anything like a player piano.  However, today,
too many rebuilders are misusing it in applications like the bottoms of
pianos, etc.

Despite its strength, plywood is not waterproof unless it happens to
be made to marine specs.  But marine plywood must be sealed, or one
lamination will still expand on top of another and wrinkle up and crack.
Besides, after steaming, the wood is never the same.  It is too porous and
grainy in my opinion, so you have to buy finished plywood, and because of
its tremendous expense, particularly in 1" thick sheets, you don't find it
on these replacement piano bottom boards.  Then the voids mentioned by
D. L. Bullock cannot be anticipated, so when replacing the pedals and
heavy equipment, pumps, and so forth, the plywood is often discovered not
to be able to hold screws at those critical places where you had counted
on it!  You'll definitely sit there, wondering what you are going to do
next!

I use solid poplar for most of these applications.  It looks worlds
better than plywood, finishes beautifully, holds screws wonderfully.
Like any other wood, you have to pick poplar carefully.  A bottom board
made from quality poplar is authentic and original.  You can buy 1-inch
thick poplar here, and butt-glue a wide plank with hot hide glue, then
plane it down, and it becomes a factory job.  That's easy, fast, and
sure, because you are not in for any surprises later, and neither are
your customers.

As far as holding screws in end grain, no wood -- not even plywood --
is satisfactory for that.  For end grain, a cross dowel is the best
solution.  That doesn't take a lot of time.  But if you want to do it
even faster, soak the screw hole with super glue and spray with the
liquid hardener after the glue has soaked in.  You'll think you're
screwing into iron!

Craig Brougher