How Long?

[Lori Kleinberg]

I have a 4X8 sheet of 1/2" plywood that is pretty badly cupped . I cut it in to 3 pieces (rough dimensions for what I need). I then clamped it to a perfectly flat surface. My question is how long to leave it clamped before it will be somewhat flat . By the way it is not Baltic Birch nor is it the cheapest stuff though it did come from the borg.

[Mike Henderson]

My experience is that it never stays flat. I would purchase a new sheet of quality plywood if you really need it to stay flat.

Mike

[Terry Flowers]

I agree with Mike. It may never flatten out. It may be useable anyway if you are using it in a structure that will hold it flat, such as partions in dados.

Terry

[Greg Cole]

I've heard that you can flatten cupped plywood, though never tried it. You supposedly place cupped plywood with the cup facing down, wet the side facing up and let it sit in the sun until dry. Aagin, I am not sure if it works or how well, but it's worth a shot if you don't want to head to the big box store and get another sheet.

[Lori Kleinberg]

Thanks for the answers. I was going to use as a frame for a 3 step thingy to help a dog onto the couch. I will leave it clamped for a bit and see what happens.

Happy Holidays

[glenn bradley]

I'm with Mike. I have never had success altering where a board wants to go unless it is to be fastened or captured reliably.

[John Miliunas]

Lori, I think I would simply frame it underneath to help "pull" the cup out. Once ply is cupped, I've not seen it come back flat. The wetting down method may work but, only if that piece of the ply structure is what is causing the cup. However, the cupping may have easily come from one of the inner plies.

[Mike Henderson]

Thanks for the answers. I was going to use as a frame for a 3 step thingy to help a dog onto the couch. I will leave it clamped for a bit and see what happens.

Happy Holidays

Since you're not going to use it for fine furniture, is there any way in the design to use 1 inch supports instead of 1/2 inch? If so, take two of the pieces of plywood and glue and screw them concave side to concave side to make a 1 inch piece.

I reaching here but it's the best I can think of.

I hope you and your family have a very happy holiday, also, Lori, and a healthy and prosperous new year.

Mike

[Lori Kleinberg]

Thanks Mike. That might be a good idea. I still have the boards clamped. Will wait to see how they look after unclamping.