What would cause a table leaf to suddenly warp?

Re: What would cause a table leaf to suddenly warp

Sgian Dubh

So, six leaves standing vertically (if my arithmetic is right). Was it a stack of leaves one in front of the other? Was it a leaf in the middle of the stack, or one next to a wall (for example), or one on the outside of the stack? In other words, could air circulate freely around each leaf, or not? Is the warped leaf cupped as well as bowed, and perhaps even in-winding as well?

Anyway, it seems possible or likely one side of the bowed (warped) leaf has experienced different RH conditions on each of its faces during the storage period. I'm trying to prompt you into thinking about the storage conditions, and what might be different about the storage of that one leaf compared to all the others.

There may be a cause for the warpage unrelated to differential RH conditions as hinted at above, but it seems logical to start with either confirming or discounting what is probably the most likely one. Slainte.

I agree with Sgian

Lee Grindinger

I'd say it's a moisture problem, one side of this leaf either picked up a lot of moisture, or lost a lot of moisture. Your attempts at straightening with clamps probably won't help, just get air flows even on both sides and hope it straightens out before Thursday.

Has anyone ever seen a board bow....

Bill Tindall, E.Tn.

from moisture? If I understand correctly the leaf is not cupped, the usual result of moisture gradient. Bowed, and not cupped. Doesn't sound like a moisture generated problem to me. I think mechanical stress is the culprit, however that happened. And I think mechanical stress the opposite direction will at least partially correct the bow.

These leaves are solid wood and not veneered something or another?

Temporary fix if needed

Bill Tindall, E.Tn.

Screw something stiff on the back side. Maybe even add spacers to each end to get a gap in the middle to pull down.

All good advice, and im with Bill,

Keith Newton

I’d cut a 2x6~8 long enough to fit between the slides, with a shim under both ends, and oversized holes for thread clearance across the middle. Then with however many large diameter screws you think it needs to draw it down and hold it there. This may not totally fix it, but I’ll bet it will take enough out to be able to use it.

Hope you enjoy the feast. I really looking forward to our gathering.

Re: Has anyone ever seen a board bow....

Sgian Dubh

Hi Bill, yes, I have seen bowing as a response to water, but not more than two or three times I could be reasonably certain that was the cause in all my time as a woodworker. In each example it was accompanied by cupping across the grain which was, if I remember correctly, the more pronounced warp.

In my original response you'll have noticed that I was probing around to see if higher moisture or concentration of water vapour to one side of the panel could be either the cause of the warping or could be eliminated. If it could be eliminated, then a search elsewhere might be in order, I suppose. Slainte.

Thanks, and some answers to questions.

Tim Greif - West of Chicago

This is an old antique table that my parents had some extra leaves made for back in the 70s. The leaves are solid oak. Unused leaves have always been stored vertically. I moved the table to my house back in 2004 and the unused leaves have been stored vertically in exactly the same place and manner for the last 14 years. They're in my basement, but the basement is dry as a bone and they are in an open area where air circulates freely. If you look at the picture I posted, each leaf has an apron piece on each end, so they act as spacers when leaning up against each other allowing airflow on all sides.

The offending leaf has no cupping or twist. Only a uniform bow along its length with the concave side down. I've had it clamped in the opposite direction for a couple days now, with no success yet.

That's why it's so puzzling to me. After 14 years of storing all the leaves exactly the same way, this year one of them decides to warp (bow). I see no chance for a mechanical cause of this the way they are vertically oriented. And only one has suffered this effect. I'm clueless why this happened.

Re: Thanks, and some answers to questions.

Kneale Brownson

Can you do the clamping with some sort of flat surface back in the basement?

While the basement may be "dry as a bone" as far as visible moisture is concerned, is it a different temperature from the rest of the house? Is the humidity identical?

They're all the same Jim....

Tim Greif - West of Chicago

All are finished on all sides and edges. I can find no difference in any of the leaves with regard to finish.

My former Mother in Law. NM

Re: Temporary fix if needed

Wood3rz

Yes, you should use the spacers for that

Re: Thanks, and some answers to questions.

Barry Irby

I have been told that the way to "fix" this is to put it out in the yard with the concave side down and the convex side up facing the sun. The theory is that the "short" side will absorb moisture from the earth and the "long" side will lose moisture when heated by the sun. I have never tried it with anything finished, but have seen lumber warp and unwarp (?) many times when flipped over next to the construction lumber pile when I was building. We used to play with pieces to see if they would do it again.

The alternative would be to have two people sit at the kids table. I am approaching 70 and never got to sit at the adult table at a family gathering.

That isnt good advice for this problem.

Keith Newton

That might work for cupping just fine, but not for bow. It would probably induce some cupping without seeing any change on the bow.

Sometimes a board which was sawn straight will bow right off the mill. When it is stacked and stickered it can take a set as it dries, but there might be some residual stress that wants to return to that initial bow.

When we steam bend wood, we want to get the whole thickness of the wood up to at least 210*, which softens the lignin between the cells, then bend it far enough for the cells to slip and take a new set. Kiln drying likely didn’t get the wood that hot, and even if it did just pressing this small amount of bow wouldn’t cause any cells to slip to form a new memory.

Sometimes you can screw around with a problem until the cows come home, and never get a satisfactory fix. Sometimes it’s just easier to make a new one from scratch.

Re: Thanks, and some answers to questions.

Sgian Dubh

Hi Tim, with your additional storage notes I can't see any obvious cause of the bowing that's resulted. I think you're unlikely to be able to force it into straightness through clamping it down as you have, as you seem to be finding out.

It seems to be one of those mystery warpages, or at least me it is. Perhaps your best recourse is as both Bill and Keith have suggested; to pull it straight with a bearer running lengthways and screwed in place so that it's at least usable. Slainte.

Don't give up straighting it

Bill Tindall, E.Tn.

Wood is plastic and it will respond to stress by changing shape. We all know that a shelf loaded to where it deflects will acquire a "permanent" bend over time. So will improperly supported wood in your lumber storage. Given enough time and stress the shelf will bow, even at room temperature. How fast depends on temperature and humidity. I have no doubt that if you put enough stress on the leaf that over the course of weeks to months you can reverse the bow.

A quick irreversible fix would be to make 3-4 scoring cuts across its back, about 1/2" deep, which will make it flexible. If flexible enough the leaf locating pins will keep it flat in use.

Re: Don't give up straighting it

Sgian Dubh

Bill, you're describing creep deformation in which a small load, well within the elastic limit of a supporting structure, e.g., a shelf will, given time, turn into permanent plastic deformation. A good example is a bookshelf relatively lightly loaded that eventually takes on a permanent bend with the concavity facing upwards.

Given Tim's description of the storage of these leaves, i.e., vertical, I think the cause of the original deformation is still a bit of a mystery. Nevertheless, you're suggested solution of a bearer (or perhaps bearers) to straighten the piece might be as good a solution as any in that it will hopefully induce creep deformation in reverse of that described above, i.e., to straighten the leaf.

Your alternative of a series of cross grain trenches would also work, but the risk with that solution might be a series of visible facets.

It seems to me that both your proposed solutions haver merit, and it's up to Tim which one he tries.

Two more 'solutions' might be considered.

1. Scrap the leaf and don't replace it, meaning a somewhat smaller maximum table size.

2. Scrap the leaf and make a new one with all the attendant grain, moulding and colour matching issues.

3. Note: I offer neither 1 or 2 above as serious options, i.e., they're offered rather tongue-in-cheek. Slainte.

tongue-in-cheek- maybe not

Bill Tindall, E.Tn.

It is oak and likely not more than simply stained. If the molded edge is not complex it may be entirely practical to reproduce the shape and a good approximation of the color and luster.

In use it likely will have a table cloth on it so really what it looks like may be irrelevant.

I hate loose leaf tables!

Re: tongue-in-cheek- maybe not

Ron in Sterling, CT

Back in the forties, while growing up, we had an old "black" table in the dining room. In order to seat all of the family one Thanksgiving, my dad made a 12 inch wide leaf out of pine. No stain, no finish. With the table cloth on nobody knew the difference and everybody enjoyed the feast. We went on to use that leaf without finish for several more years until Mom got a new dining room set.

Ron

Re: tongue-in-cheek- maybe not

Sgian Dubh

"It is oak and likely not more than simply stained. If the molded edge is not complex it may be entirely practical to reproduce the shape and a good approximation of the color and luster.

That's true really I suppose, Bill. I guess it depends upon what skills Tim can bring to bear on such a project, relatively minor for myself, and you I believe. But I don't know Tim's skills - they may be more than adequate, and if they are then making a new leaf would be a very viable option. Slainte.