How to flatten 3/4" plywood (24" x 24")?

[Tom Burgess]

I've been holding onto this 24" x 24" scrap piece of cherry plywood for a long time (maybe too long ;)). I finally have a use for it, but laying it on the table saw shows that it's warped :( across opposite corners. It's just two cherry veneer faces with 7 ply of some softwood between, but I don't want to purchase another full sheet.

Is there a tried-and-true method for flattening a piece like this?

[Jeff Duncan]

I don't know of any dependable method for flattening a piece of ply that's warped. One exception would be if you can pull it down to the piece your making with fasteners or other mechanical connection.

good luck,
JeffD

[Frank Drew]

Tom

Not that I'm aware of. I've tried weighing in the opposite direction but that didn't work. The methods that people use on warped solid wood (with varying results) would likely be ineffective on ply.
Plywood can be such a nasty material for exactly this reason.

[Jason King]

I've had the best luck trapping the misbehaving ply in dados of a larger assembly. Depending upon what you plan to do with it, you may be able to build a flat frame around it, force the ply inside and then use the frame/plywood for your project.

[Malcolm Schweizer]

In many cases the warpage is due to uneven drying, which causes one face to shrink, thus causing the plywood to bow in towards the face with the least moisture. Try leaving it out in the sun with the concave down. It only takes a short time- in some cases just 30 minutes or so, so check on it often. This may or may not work, but has worked many times for me with warped plywood.

[Larry Edgerton]

What Malcolm said but you can use a cheap worklight on that size. My old shop had a radiant tube heater that I would use for this purpose when needed. Five minutes and it was flat, ten and it would be cupped the other way.

Larry

[Sid Matheny]

I have at times used MS on both sides and clamping it flat on a good flat surface and let it set at least 24 hours. Don't always work but it has worked better for me than anything else.

Sid

[Tom Burgess]

Thanks guys, for all comments.

Malcolm: Thanks for the insight regarding bowing toward the dryer side. I've always treated plywood half-sheets and smaller as if they were totally inert (and basically indestructible...). Lesson learned. I would put it out in the sun, but it looks like nuttin' but "winter gloom" until about April (doh!). I wonder if spritzing the concave side very lightly with water (a mist really) would assist the process you suggest?

Larry: I have a HALOGEN! work light that gets 'hotter than the hubs o' hell' so maybe I can press that into service. Again, I wonder if misting 'the dry side' of the panel with water would help the process along. I'm glad to have a fix, ecstatic to have a five-minute fix. I hope it works. Thanks.

Sid: Thanks for adding to the discussion. What is 'MS'? And I appreciate your Louis Nizer quote, “A man who works with his hands is a laborer, a man who works with his hands and his mind is a craftsman, but a man who works with his hands, his mind and his heart is an artist.”

Thanks

[Sid Matheny]

MS = Mineral Spirits


Sid

[Malcolm Schweizer]

Thanks guys, for all comments.

Malcolm: Thanks for the insight regarding bowing toward the dryer side. I've always treated plywood half-sheets and smaller as if they were totally inert (and basically indestructible...). Lesson learned. I would put it out in the sun, but it looks like nuttin' but "winter gloom" until about April (doh!). I wonder if spritzing the concave side very lightly with water (a mist really) would assist the process you suggest?

Hello Tom,

I often forget that it gets cold and cloudy in some parts of the world! A light will work just fine. It is better to dry the moist side than to try to moisten the dry side.

[Tom Burgess]

Thanks Sid and Malcolm.

I'll try the Malcolm+Larry method of dry plywood under hot halogen light.

If that doesn't work, I'll try it again but with a very light misting of water on the dry side.

If that doesn't work, I'll wipe on mineral spirits and clamp it flat for 24 hours (first 10 minutes under the halogen light) per Sid's method.

If that doesn't work, it's firewood. :D

[Mike Hollingsworth]

10 minutes on the lawn in the sun.

[Tom Burgess]

If I were living in sunny "Pasadino, CA" that might be an option in late November, but here the plywood would be covered in snow.

BRRRRR! :eek: