Unwarping a board.


GNiessen

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I have a White oak board that I had cut for use as a door threshold and even sealed the surface with an epoxy paint. And it decided to warp on me while sitting in the shop for a couple of months waiting to be installed. Is it a lost cause to try to wet the concave side and try to get it to straighten a bit?

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the only way to get it perfectly flat again is to mil it using the jointer (or a planer sled) to flatten one side, the run the other side through the planer to both faces parallel. Unfortunately, you will loose thickness (possibly a lot if it is severely warped) in this process.

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Did you paint all sides? Almost sounds like just the top was painted, which is where the error was. You have nothing to lose. If it is concave down because the underside wasn't sealed, get a big sponge from the big box and get it pretty wet with basically boiling water. Lay out a couple garbage bags and roll the board up like a subway sandwich so the entire board is wrapped with the plastic. Clamp concave down on a flat bench along its length. Leave it at least 24 hours (not overnight, 24 hours).

Worse case, you're out a quart of boiling water.

After 24 hours, unroll it and check it. Should be much better. If not, you can repeat although I'd say twice is about the limit. If you need a second time, put a small shim under each far end to overbend it a bit.

Once straight enough, paint any unsealed surface with that epoxy paint. Try keeping it clamped so it gets in and sets while straight.

Variants of the above in different circumstances worked for me.

If that doesn't work for your situation, post back for another simple idea to fix it.

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The only way I've been able to straighten warped stock is to flat laminate it. That's the opposite of a bent lamination, bandsaw the piece into slices then glue them up clamped to a flat platen or in a vaccuum bag. It's almost always not worth the effort.

If this is a threshold, what's stopping you from nailing it down and painting it? If it's thin enough the nails will hold it.

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I am making the threshold of two parts, a 3/4" flat bottom board that fills the threshold and stops at the tile of the entryway. And a shaped piece that extends a little out over the tile and then rises up to fill the gap under the door and then tapers down to the bottom piece. The main warp is on the thin part that tapers down to just 1/8" to blend into the bottom threshold. I was going to screw down the bottom board and then epoxy the top piece on in place. That way the top would cover the screw holes. But I have no way to clamp it. So I'll have to count on some weights.

I have it clamped in a jig now with a shim to over bend it a bit. I only used damp rags to add moisture. And it seems to be bending a little more each day. Tomorrow I'll try letting it dry while clamped and then see it it holds its shape in another couple of days.

70# of weight was not enough to hold it flat. So I may have to glue it together and just plug the anchor holes.

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