Join Date: Jul 2008
Location: Dickinson, Tx. / Somerville, TX
Exactly what are you making, how thick is the plywood and how hard is it to press flat?
The reason I ask is that it may not be too much of a problem to 'pull' flat against a frame such as a table apron.
Anyway, you might try wetting down the concave side with hot water, a LOT of hot water, then flip the board over and add weights to the bulge of the convex side. This air movement will help shrink the upper convex side and swell the bottom concave side to flatten out the board. It should work in theory but it never worked for me. If it is an important piece of a project, I would unquestionably use a different piece and use this piece latter on down the line when you need small pieces. I learned a long time ago that trying to use something 'inferior' to save money will cost you a lot more in the long run.
Retired woodworker, amongst other things, Sold full time cruising boat and now full time cruising in RV. Currently in Somerville, Tx