John Tuttle asks about correcting a warped keybed on a piano. The
classic way to correct a warp is by hammering numerous thin veneer
wedges into saw cuts you have made with glue to hold them in. The
keybed however is a structure which is made kind of like a door and
would be difficult to fix completely that way. Since the grain is
running with the keybed on the long members, and since they are
separated by panels, I am a little questionable as to how all three ( I
presume) members could warp the same way. Usually, you have perhaps one
member warp, but not all of them, until it looks "like an elephant sat
down on it."
Sometimes we don't always see exactly what the problem is at first
glance. Granted, if this is a really "el-cheapo" pianer, then pull out
that keybed and replace it with your own version. It was obviously made
from poorly cured and dried wood. No sense asking the company to
replace it with another one of their famous keybeds, is there? On the
other hand, you just may have a warp in one of the rails and it just
looks like the entire keybed to you, or it could be that the keyframe
can be straightened above the keybed with shims.
If it is fixable, the way I'd do it is a little bit here and a
little bit there. A straight edge finds the bow, and a straightedge and
paper front rail punchings will find the twist. Take some of it out
with veneer wedges, some with veneer shims, make sure the key frame is
flat first, then reset it using paper and veneer.
If you think the extreme humidity is to blame, you have two
options: You can either remove the keybed, soak it, wrap it in
newspapers and clamp it in a heavy press with just enough overbend to
fully correct when it's dry, or you can make another one using southern
poplar found up there in a lumber yard. Pin plank material makes a
great press when clamped on edge.