Q: I have several pieces of A-B plywood and they have twisted after I brought them into the work area. I am trying to get them flat by putting some reverse twist in them and holding them that way. If that does not work (I do not see any improvement yet), what next?
A: We are dealing with the First Law of Working with Wood: If the moisture content never changes (good luck!), then wood will not change size or shape from day to day.
The tendency to twist is inherent in the wood veneers used for making your twisted plywood, especially some of the pines. It would be common for the plywood to be flat when it leaves the press during manufacturing; heat and pressure will eliminate twist. But then if the plywood cycles a lot in MC, it will likely warp if this twisting tendency is in the veneer initially.
It is my guess that the supplier of your plywood stored the plywood in an unheated shed where the humidity of the air was high. The wood regained MC slowly. It was only when you quickly re-dried the pieces in your dry work area that this natural shrinkage occurred. Trying to untwist the wood is not likely to work well at all. I would encourage you to return the wood to the supplier and get some new pieces. Otherwise, use this plywood for small pieces or where warp will not matter. Do not expect to be able to hold if flat, such as with a table frame. (Note: The twisting tendency of some pieces of plywood is hard to prevent when manufacturing veneers and plywood. Most manufacturers understand this and, in my experience, will work with you when twisting is severe enough so that you cannot use the piece.
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