Cupping After Resawing

[brnhornt]

Hi Gang...question for the masses,

I'm starting the FWW Bow Arm Morris Chair, and the first steps are to make the bent laminations. My first attempts at resawing some QSWO ended in disaster. I quickly realized how dull my blade was, and how out of tune my bandsaw was. After purchasing a new blade and bearings...she's humming pretty.

Monday, I head down to the mill and pick up another chunk of QSWO to replace the firewood I made during my first attempt. Last night...I get to work. Get the board squared up and ready to go. I proceed with resawing and the two boards I did came off nice and perfect...3/8" (from a 4/4 board) slices. I set them aside, moved the extension cord and then my dust collector hose over to the drum sander when I noticed the cupping. Both boards had cupped rather severely. Definitely more than I can overcome during glue up. Feeling rather dejected at creating yet more firewood, I put everything away and went inside before I messed anything else up.

So...what the heck did I do wrong here? I've been reading about casehardening and other stuff...but I don't have the budget to go pick up any more lumber for this project....and I think I have JUST enough boards remaining to produce the arms...I'm now honestly gun shy that I'm going to make a mess out of everything else.

The only plan that I came up with, is to resaw the 4/4 boards that I have remaining in half, sticker, and then clamp them down and wait a week...hoping that the extra material holds them in shape...then after a week, plane them down to final 1/4 thickness. I'm also reading that while the initial cupping can be dramatic, just spay the inside face with some water, sticker and clamp for a couple of days and all will be well.

Any ideas from those who have gone thru this frustration before?

Thanks!
Kevin

[Routerman]

I'd be surprised if it didn't cup.
Air-dried less of a problem but the re-saw cup is typical.
& typically you re-saw over size, let the stuff gestate and then mill to net.
Could be days or weeks later before the material equilibrates.

[handi]

Routerman said:

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I'd be surprised if it didn't cup.
Air-dried less of a problem but the re-saw cup is typical.
& typically you re-saw over size, let the stuff gestate and then mill to net.
Could be days or weeks later before the material equilibrates.

---

^^ this^^
For any fine furniture work I want to do, I ALWAYS prep the stock keeping it slightly over sized, because it will move. I sticker and stack it for a week, and let the stress "relax" out. Then I prep it all over as if starting from rough stock.

My game table was milled this way in NH, assembled on St. Croix in the Virgin Islands, and has since lived in Tennesee and now Florida without ANY unexpected wood movement.

I also never expect to Resaw a piece in half and retain both halves unless they will be planed down a lot. You can't usually get two dead flat 3/8 from a 1" piece.

Ralph

[Dan Moening]

Quote:

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just spay the inside face with some water, sticker and clamp for a couple of days and all will be well.

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The inside face is likely where the remaining moisture exists. IMO you need to equalize the moisture content by spraying the outside face.

I had this happen recently with some sugar pine. Same thing ... 3/8" from 4/4 stock.

I sprayed (heavily) the outside faces, clamped up with stickers, wrapped in a tarp and set them in the sun for a week (100+ degree days elevated the temp under the tarp to 120).

Of the 10 boards 6 came out flat, the remaining 4 were better but still cupped a bit.

I've read that professional kilns mitigate this by steaming lumber for a couple of hours, but I had no way to duplicate that process other than wrapping in a tarp to increase the temperature.

[YSU65]

It sounds like there is just residual stress in the wood. I could come from the drying process or is inherent to that piece of wood. I also had trouble with flat sawed wood that was initially OK but was left sitting on a bench when we had a weather change that caused the wood to cup. I let mine sit in the sun with the cup side down and it eventually came almost back to flat. Let is dry for a while and see if it starts to flatten out. I have had initially flat 8/4 stock turn into propellers when I cut strips. Good luck....Tom

[jteneyck]

If the wood did not have any internal stresses and was in equilibrium with your shop it wouldn't cup. Sooooo, that means it was one of the two. How long have you had the wood in your shop? If it hasn't been at least a couple of weeks that would be a red flag to me.

All may not be lost. If the problem was just due to non uniform moisture in the board, they may very well flatten back out once the moisture equalizes. And you don't need to spray them, clamp them, etc.. They will do it on their own if they are going to at all. Just leave them on edge or standing up so that air can freely circulate all around them and they will flatten out after a couple of days. If they don't the problem was due to internal stresses and the only solution to that is to slice the next batch thick and then joint flat and plane down to final thickness.

White oak is a cantankerous wood. It has high drying shrinkage compared to red oak and stresses often develop if it's dried too quickly. If it turns out that the problem was due to internal stresses I would look for another source of white oak the next time.

John

[brnhornt]

Thanks guys...the wood had only been in my garage from Monday afternoon to last night...

I'll let it settle for another week before I try again. This time...I'll just slice the 4/4 board in half and then set it aside and plan on planning it to the 1/4 I need a few days or a week after. If the wood cups even after all of that...then I guess I can only chalk it up to stresses in the wood possibly due to bad drying techniques...and won't be shopping at this particular mill in the future....

[MichaelMouse]

You may find the cup has gone away by the end of a week. Rift or quarter saw won't cup from drying stress as flat sawn will. You have a piece of "case-hardened" wood - which should relax its way to flat or nearly. Let it acclimate.

[Guest]

I agree with John. If the boards don't flatten out on their own and you have to buy more stock, here's a suggestion: Instead of trying to resaw 3/8" stock from 3/4", start with 8/4 stock. Resaw 1/4" slabs from each face and set them aside. Saw your 3/8" pieces from the remaining interior of the board. The moisture content of the 8/4 board will be more uniformly dispersed the nearer you get to the center. There is a pretty dramatic differential in the moisture gradient at the outside edge, which causes the slabs cut from the edges to cup as soon as they are separated from the board. If you remove the outside pieces first, slabs cut from the interior of the board will cup less, if at all. If they do cup, they should flatten themselves much easier and quicker than the outside pieces.

My $.02.

Hank

[brnhornt]

Thanks Hank...I'm looking for 1/4" material...and none of my local vendors had QSWO in 8/4...