I have some pieces of 5/32 aircraft plywood that are about 1' X1'. They have a modest warp to them... about 3/8" in 12". What is a good way to make them flat? I'm going to use the material for fins that will be about 4"X 8". Would it be better to cut the fins then try to flatten them?
Steaming the wood will make it expand, so steam them inside the warp. I got some fins in a kit that were warped along the root edge. To straighten them out I got out the spaghetti pot and got a good boil going. it's tricky the first time you do it so start out with the fin about 18" above the water, and check your progress frequently with something that you know is flat, like a piece of glass, or the edge of a metal ruler.
5/32 is 3-ply and particularly prone to warping. the 1/8 is actually 6-ply and seems to be more warp resistant. Before they got in bed with Estes, NCR used to use the 5/32 stuff because it's a LOT cheaper. I use it a lot for centering rings and other places where warping won't be a problem.
Any my plywood pet peeve, especially among kit vendors: Plywood grain direction matters as mush as balsa grain direction. Sure, that 1/8" ply is 6 layers, but 4 are one direction, same as the surface, and only 2 are perpendicular. Yet it seems that more kits have the grain running parallel to the root, rather than parallel to the leading edge. It does make a difference!
Bob Kaplow NAR # 18L TRA # "Impeach the TRA BoD" >>> To reply, remove the TRABoD!