Hi all. A chessboard I had made for me is quite bowed, and I'd like to
fix it. It is big though--almost 22" square. The stock is thick enough
that I think this could be corrected.

Can I find a planer at a furniture shop so big? Otherwise it looks like
a lot of sanding is in my future.

Getting it flat by hand: I was thinking of glueing the sand paper on a
board and then placing my chessboard face-down and moving it back and
forth for a few weeks. I don't have a better idea on getting it flat,
and I probably can't hold a belt sander at the right angle to fix the
board and not ruin it with wrong and excessive removal.

I'm hardly a woodworker so a better solution is always welcome.