A Method for Correcting Warps

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Forum topic by therealSteveN posted 07-01-2019 08:04 AM 350 views 0 times favorited 7 replies Add to Favorites Watch
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3378 posts in 1026 days

07-01-2019 08:04 AM

You are reading through, the whole time saying hummmmm lookie there, complete with pictures. Then when you get done you read the comments, and say, yeah I had heard this too.

Being Flexner, he had to throw in doesn’t matter if it’s finished on both sides.

It makes you want to look back at the last subject Flexner typed about…. Should I finish on one side (Show side) or both…... Not like that question has never been asked.

Discuss. He does say it’s a work in progress.

-- Think safe, be safe

7 replies so far

View bondogaposis's profile


5492 posts in 2803 days

#1 posted 07-01-2019 01:11 PM

My first impression was that he was wetting the wrong side, then by further reading I realized that by confining the sides the wetting of the long side will cause compression of the cells on that side resulting in a flattened board once it dries out. Interesting, I’m not sure how practical it might be, but it is always interesting to learn something new about how wood behaves.

-- Bondo Gaposis

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3378 posts in 1026 days

#2 posted 07-01-2019 03:29 PM

I guess the reason I posted this was because I have seen some threads, not just here, where if folks were close, I’m pretty sure gun play would have ensued. It was just Bob is considered by many as being quite knowledgeable, and he had pictures showing what he thought to be true. Sometimes a rare combination in a woodworking thread.

I’d never seen anyone post pictures of their theories on this before. I thought it was pretty neat, so figured I would throw it out there.

Certainly both things are subjects that get posts about on forums such as this one.

-- Think safe, be safe

View CWWoodworking's profile


528 posts in 630 days

#3 posted 07-01-2019 04:21 PM

His last subject is a straw man argument. Finish is not going to stop wood movement.

Personally I would never use this trick. Just easier to rip it, glue it, and sand it flat.

View Jerry's profile


3229 posts in 2100 days

#4 posted 07-01-2019 05:39 PM

I have flattened a lot of boards by wetting the cupped side and letting them sit with the cupped side down on the workbench until they resemble flat, but never the bowed side…

They don’t ever get perfectly flat, but flat enough to run through the planer to finish the job. The trick then is to let them acclimate for awhile to make sure they stay flat, then you can use them.

-- There are good ships and there are wood ships, the ships that sail the sea, but the best ships are friendships and may they always be.

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James E McIntyre

405 posts in 1744 days

#5 posted 07-03-2019 07:51 PM

This is a topic that should of interest to almost all woodworkers.
It turns everything I though about removing a cup from a board upside down.
I’m going to experiment with Flexner’s technique.

Do you know why he placed the clamps on the sides of the board?
Seems like the clamps would prevent the cup from flattening out.

Thanks for posting this topic Steven.

-- James E McIntyre

View jacww's profile


38 posts in 1459 days

#6 posted 07-03-2019 09:34 PM

From the caption of the 4th picture:

“To encourage compression shrinkage of the bowed side, you can add clamps.”


View Woodknack's profile


12870 posts in 2832 days

#7 posted 07-04-2019 06:17 AM

Seems like the clamps would prevent the cup from flattening out.
- James E McIntyre

That’s exactly what he is doing. If you have a loose hammer handle, you can soak it in water and swell the wood to tighten it up but the compression crushes the wood so that when it dries it’s even looser than before. Flexner applied the same idea to a cupped board. The clamps prevent the top from expanding so the expansion compresses the wood cells which shrink when dry and flattens the board. He came up with the idea because he believes that tables with unfinished bottoms cup because they are wiped down with damp cloths everyday causing compression shrinkage, and not because of unequal moisture exchange through the bottom.

-- Rick M,

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