DIYbanter - View Single Post - Bowed chess board...would like to find a big planer

says...

Both top and bottom need flattening. I already flattened the bottom
(just the bottom of the frame needed it; it has a recessed panel). The
bottom has bowed since then and I think the top as well. Maybe I
accelerated that process by removing material from the bottom of the
frame?

As I said above, the squares are 3/4 walnut and soft maple, the frame
3/4 soft maple, the panel looks like ash.

I'll give some effort over time and try to fix it. If the wood doesn't
move over several months I'll put a finish on it.

If all goes well I guess I should finish the underside panel as well or
face the same problem later as leaving just the top finished may induce
stress?

Thanks for your reply John.

If the board has unfinished solid wood, then that is probably why it
warped. If the bottom panel was unfinished solid ash, then it would
expand and contract across the grain making warp inevitable. A plywood
base might have actually been more stable, but in any case the builder
should have sealed the board top and bottom to minimize moisture
exchange with varying humidity. If you flatten it and leave part of it
still unfinished, then it will likely warp again. Your best bet is to
flatten it, and seal any exposed wood with shellac. Unfinished wood may
be the root of your problem--don't leave it that way for long. But if
for any reason you want to remove Shellac, you can with some denatured
alcohol and elbow grease. Shellac would be a good choice for a finish
on a chessboard, and is an excellent base coat for just about any other
finish.

You might want to try exposing it to differing humidity levels to see if
it straightens out some. A cheap humidifier, if you don't already have
one, in a small room could raise the humidity, and raising the heat in a
small space can lower it. Of course the effects, if any, could take a
while to see. I haven't actually tried this, but in theory it may bring
the board back to a condition more like when it was new. You may be
able to guess if it gained or lost moisture from the warp. If the board
has a concave warp, then it probably gained moisture, and vice versa for
convex. Of course, it could be inherently unstable since it is
basically a two-ply laminate of very different wood layers. You may
want to seal it and leave it in the conditions where it will spend most
of its time for a good long while and let it finish doing its thing and
then flatten it.