How to flatten warped plywood?

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Well-Known Member
Dec 31, 2003
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I just bought a 12" X 48" piece of 1/8" thick aircraft plywood that I want to use for some fins.

The hobby shop only had two pieces and both were warped.

My fins are going to be about 7" X 7" so the warping will be noticable. Is there a way to flatten this out?

Thanks for reading!
I have heard that a hot iron with steam often does the trick.

You will probably have to place the fins under a heavy object on a flat surface afterwards, to dry for several days.

You may want to fiberglass later, to prevent re-warping.
is it permantly warped or only bent?

vjp has some good ideas....ecspecially fiberglassing
I got some 1/8 birch ply fins laser cut from BMS and they arrived warped a bit.

I was able to remedy it by sprying them with water from a squirt bottle and then bending them back against the "warp" by hand. As soon as I had it looking satisfactory, I immediately glued the fin to the airframe with a thick bead of CA. After all the fins were applied in this way, I applied fix-it epoxy clay fillets.

That was several months and a couple of launches ago. They still look fine.

Of note, I was suprised at how tough plywood is, and how much pressure I could apply bending out the warps without cracking the wood.
I was thinking of the steam iron idea... not sure what kind of luck I will have.

Soaking in water is another thought, but I need the fins to be ready fast and I don't know how long it would take to dry them out. The launch is on the 15th and I haven't started my project!!

Ryan S., not sure what you mean. I figure if it's warped, it's permenantly bent.

So I had another thought, maybe I should use G10. Anybody know of a good supplier that will cut custom fins out of G10?

All I could find is Public Missiles so far. I'll be sending them a drawing tomorrow for quote. Maybe this should be another thread.

Thanks again for the ideas.
I haven't ordered from Giant Leap yet but others in my area have. No complaints.

I see that he does have a lot of variety of G10, but I am not sure if he does custom fins (like, from a RockSim file) or not. I wouldn't be surprised though.

Here's the link.

Len Bryan
I decided to spring for the custom G10 fins. I sent a quote request to both PML and Giant Leap Rocketry. PML had an answer within hours (haven't heard form GLR yet). I made up a list of things I wanted to buy and placed the order yesterday (thursday). They said I should have my order by monday!!

Thanks for all of the help guys! I've got to get rolling on this project if I expect to have it ready by the 15th!