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How To Make Warped Plywood Flat???

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How To Make Warped Plywood Flat???

Old 01-17-2009, 03:16 PM
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Blackout
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Default How To Make Warped Plywood Flat???

I bought a sheet of 5/32 inch Sig aircraft ply from the LHS. It has a slight warp in it. Anyone know a good way to make the sheet flat again???

For what it's worth, most all the sheets were warped at the LHS. I bought the best one there.

Thanks.
Old 01-17-2009, 03:39 PM
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500 lb. koolaid man
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Default RE: How To Make Warped Plywood Flat???

All I can think of is, soak it in water then immediately put concave opposite pressure on it for 12-24H. maybe someone else has better advice though.

I haven't actually read it, but try this
http://www.homediscussion.com/showthread.php?t=81780

also google "fix warped wood"
Old 01-18-2009, 12:00 AM
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Default RE: How To Make Warped Plywood Flat???

Place a wet towel over it and iron it flat with high steam. when it steam dries should be flat. this also works well for taking out dents in the wood.
Old 01-18-2009, 10:40 PM
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Default RE: How To Make Warped Plywood Flat???

I have straightened boat kit parts by spraying with 50/50 amonia + water, two sheets of glass and a full day of sunlight on a hot day.

A think towel on each side might help it evaporate a little better.

The day I did this, all it seemed to do is sweat inside the glass but it eventually dried out. It seemed to trap the moisture a little too good.

Amonia temporarily softens the cellulose fibers with wood and allow it to relax until it dries.

I stole the smoked glass doors off my stereo tower cabinet for the day.

Expect a bit of raised and exposed grain when doing this. These were internal bulkheads for a hydro, so it wasn't very critical that I saved the grain on it. They could probably be sanded smooth again if I wanted.

I think I have the right idea, but it's not perfected yet.

Ply doesn't have to be very straight in its free state unless your trying to span a very large open area without any support.

My wood sections were small but curved really bad by being out of the die-cut sheet loose in a box for 35 years. They aren't whooped that bad anymore, but still not straight enough without using small spring clamps and short sections of aluminum angle clamped to each one when I go to mock up the hull.

Using small angle iron (aluminum) and spring clamps isn't a bad way to go either way when building. Boat ply is usually too thin to have any kind of straightness to it to start with. As long as it can be HELD straight while its glued, thats the important part. Once it is glued, the clamps can come off and usually there's enough support within its glued structure to hold it straight.
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Old 01-19-2009, 06:49 PM
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Default RE: How To Make Warped Plywood Flat???

Good ideas, thanks! I'll give them a try.
Old 01-24-2009, 06:55 PM
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Default RE: How To Make Warped Plywood Flat???

Warpped wood is usually caused by uneven dehydration of the wood, i.e. sun or dryness on one side. The damp towels on both side can balance out the wood again.
I use to have the problem of trying to bend the wood across a deck and it not wanting to go my direction. Sometimes you can use a warp to your advantage in those compound bend areas. We also used home made bean bags to hold our wood in place until the adheasive set. Good luck. Al
Old 01-25-2009, 08:20 PM
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Default RE: How To Make Warped Plywood Flat???

Hey Jetpack, you hang out here too?...I have used alcohol to bend wood,, dries quicker than the ammonia/water,,I imagine it would work to straighten wood as well, nice flat surface and several books to flatten it out......Rog
Hey if I can bend balsa around a drink can, flattening ply cant be too hard
Old 01-26-2009, 10:12 PM
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Default RE: How To Make Warped Plywood Flat???

How about this? Put some epoxy resin and 1 oz fiberglass on either side of the plywood. Lay the "sandwich" down on a flat surface with a piece of wax paper as barrier. Then place another piece of wax paper over it and something heavy like an anvil on top of the whole thing. When the epoxy resin cures, the piece should be straight and also quite a bit stronger as a side benefit.
Old 01-26-2009, 10:17 PM
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Default RE: How To Make Warped Plywood Flat???

Yep a pre-finish with epoxy would help because it wets the wood...well at least the outer plys. I would expect some spring-back still. Bent wood is very determined to stay bent. Adding cloth would make it very much stronger. It forms an "I" beam with the wood. Aluminum honeycomb with Carbon Fiber sheeting is an extreme example of this and is a modern version of this trick.

Pre-finishing ply is how I plan on doing up some bulkheads when I go to build this next time. What works better than wax paper (it used to be wax but now its different and sticks) is using PVC Visqueen...that clear plastic drop cloth stuff painters and home builders use. Thicker the better.
Old 01-31-2009, 08:11 AM
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Default RE: How To Make Warped Plywood Flat???


99 % of ANY warping in plywood is due to it being made with 2 DIFFERENT types of wood in it.

They WILL definately swell at different rates.........Waste of time usually.

Also..... same wood used in every layer CAN STILL WARP..........layer were cut from different ANGLES of the wood GRAIN. 1 side is AAA the other is B or C grade.


They really are trying to warp all plywood if NOT used immediatly.

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