Bowed wood clarification

[David Ragan]

Hi,

I posted a couple of weeks ago about some bowed walnut. Thanks for the replies.

I had four pieces. Last wkd, as instructred, I wet the concave side with warm water and then took each pair, concavity toward each other, and secured with some 2" shrink wrap. (Called 'flat twine' by some mfg.) Of course, when paired, they straighten each other out. They are still paired up in shrink wrap. The shrink wrap doesn't cover but a fraction of the wood--all water should be able to evaporate.

Yesterday, I was looking around this forum and saw where some folks had recommended wetting the convex side, and gave a very complete scientific explanation (I loved it, but was unable to comprehend it in full.).

So-I will unwrap my walnut in a couple of days, it may still be bowed. Is there a consensus on what to do if it is still bowed? I don't have the $ to go buy more.

Thank You, David

[Dennis Ford]

I am sorry to be a wet blanket but; I suspect it will be bowed when you unwrap it and that it will defy attempts to keep it straight.

[John TenEyck]

Sorry I didn't see your first posting. If your wood was not at EMC when you first worked it, it may straighten out on it's own when it does reach equilibrium with your shop. But if it was at equilibrium with your shop when you first cut it, then there is nothing you can do that will make it permanently straight and flat again other than run it over the jointer. Efforts like wetting it like you are doing now are temporary and when it dries out again the bow, cup, etc. will return. That's been my experience anyway.

John

[lowell holmes]

I think it will be bowed.
Look back at the original thread and see my post.
It was the one about ripping the board down the middle and gluing the halves back together with dowels.

I had two 2X8 s4s pieces of clear walnut that I had paid a lot of money for. They were to be the stiles for
a new boardroom door. I tried water and even the old boat builders trick of laying the boards on wet grass cupped side down.
Nothing worked.

I straightened the boards like I described and 30 years later, the door is still straight.

I was younger then and did not know better.

[Andy Pratt]

I don't feel like you are getting anywhere if you use water to artificially, temporarily, eliminate cup in a board, when the board dries out it is just going to go back the way it was. If the board was accidentally wetted on one face and that's why it cupped in the first place, just let it dry out with a little weight on the convex side and it should not be cupped any more. If you temporarily remove the cup with water and attach the board to something in the meantime (built into a project) you now have that stress on whatever you built, possibly ruining the project. I suppose there are some situations where the board would be so firmly held into place by other parts of the project that it could be worthwhile, but barring something unique I would just fix the flat in the ripping manner described above, that is the only way to really fix the problem without losing a lot of thickness on the jointer.

[Jim Matthews]

I don't see the prior post.

To clarify, is the curve over the length of the board, or across the width?
If I'm dealing with a long run, I try to laminate by resawing the board along
it's length and flipping one half 180 degrees so that the board's natural grain
pattern is in opposition. If the board moves with the Seasons, the forces cancel.

Cupping is nearly impossible to eradicate, and should be manageable by proper milling.

Severely cupped boards that cannot be planed close to flat should go back to the lumber yard.

As mentioned before, if you rip the boards in half - you can work around the curve.

http://www.mcilvain.com/wood-moves-get-over-it/

[David Ragan]

Success!
I took the plunge, ripped the wood, and used dowels to align them. I read a bit about the dowelling deal, and made a lengthwise little trough in each dowel (store-bought). Jointed the edges after ripping. used a..."WolfCraft" jig to make sure the dowels lined up perfectly-they did. But, not perfectly centered width-wise. so, when I took out what little cup was in a board, the dowels showed through on one face. Will not show.
I replaned all that, and went from about 0.68" to 0.58" Not bad?
I also have a pricier doweling jig that auto centers, but was worried about eye-ball lining them up.
Was afraid my Festool domino would just be too much trouble.
Anyway, the results area great. The different wood grain is not a cosmetic concern, and the planing went pretty smooth, with the backwards on the other half sometimes.
Thanks for the help!