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Joe Member

I have been working with wood all my life. Since the 1960's. And I have always had in my head, when you look at the end grain of a board, by the way the circles are, you can determine if it was to warp, what direction it would.

But my latest batch of wood I have gotten has gone the other way. ODD! So my question to all the smart folk here when you see wood as in the image,

"N" if it was to warp what way would it most likely warp "A" or "B"?

5/13/20       #3: Warping ...
Tom Gardiner

I would expect B. The way to remember is the rings are trying to straighten out. That is if the wood is drying after milling. The opposite is true if the wood is gaining moisture.

5/13/20       #4: Warping ...
Joe Member

That's what I always remembered thinking the grain circles want to flatten out so make a hill like "B" bit I got some that is behaving like "A" sooo odd.


5/13/20       #5: Warping ...
David R Sochar Member

Remember - wood only changes shape in response to changes in moisture in its environment.

While the terminology is anything but precise, where I am, the defect you describe is cupping. Warp has to do with curving along an edge.

5/14/20       #6: Warping ...
D Brown

It is possible that the lumber was surfaced or brought to the current thickness by removing more from one side than the other , now the moisture is not centered, maybe that is helping the cupping happen.

5/14/20       #7: Warping ...
David R Sochar Member

D Brown is right, but....

That is true only if the lumber is not dried properly. Hardwoods often have a final step in the drying schedule - called conditioning - that causes the wood to be a bit over dry on the surface, while the center comes right down to the right MC. Then the kiln operator adds some humidity to the load, putting back the water vapor that was taken in the short overdrying step.

Look up casehardening on this site and you can test some of your lumber in a few easy minutes.

View higher quality, full size image (600 X 314)

6/1/20       #8: Warping ...
Jessica  Member


Wood movement is entirely related to moisture loss or gain. Most moisture content related issues come from the lumber being too wet. But the thing to remember is lumber will swell if it's too dry.
What it comes down to is the orientation of the grain. What you have pictured below is a flat sawn board. The flat sawn surface is known in the wood science world as the tangential surface. Every flat sawn board has two tangential surfaces, with one being more tangentially orientated than the other. The surface that is more tangentially orientated is the surface that would be closest to the bark. We say the tangential surface shrinks and swells the most out of the three surfaces of wood. But because one surface is more tangential than the other, that surface will shrink or swell more than the other. This is what causes cupping.
So when lumber looses moisture, the surface that is closest to the bark will shrink more than the other. This causes the board to "cup towards the bark." This is what is depicted in image B. But if the lumber gains moisture, the more tangentially orientated face will swell more than the other, causing the board to "crown toward the bark." This is what is shown in image A.
It's true that this could be happening do to removing too much material off of one face, but only if the lumber wasn't conditioned properly. But if you have rough sawn or even S2S lumber that came through you're door looking like this, chances are it picked up moisture.

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