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Thread: Walnut Table Top is cupping

  1. #1
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    Walnut Table Top is cupping

    Advice please!
    I am making a walnut dining room table. It has breadboards for the ends that will slide out on rails so that I can extend the table to seat 10 people. I glued up the top and it was flat. But like most things, life got in the way and I neglected to get the top finished and mounted on the bottom in a timely manner. So now it is cupping a bit (about 1/4 inch) at the sides. I brought it up from my basement workshop yesterday to get it into its final “environment”. I put cauls on it and clamped it flat. I am wondering if this will get it back to being somewhat flat—or flatter than it is right now. One of the photos is the top on my workbench in the basement. the other two are upstairs in clamps.

    How long should I leave it clamped? Should I flip it and reclamp at some point?

    My plan is to finish the bottom side with wipe on poly and then mount it to the base with z clips. Hopefully that might hold it flat while I finish the top. Once that is done, I will get the breadboards attached and hopefully the table extensions working.

    Any advice would be appreciated.
    Gail
    Attached Images Attached Images

  2. #2
    The first thing I would do is remove top and turn it face down on a blanket. That will let the back get a little dryer and
    get flatter. Cauls underneath top might hold it

  3. #3
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    Wood moves (warps) with humidity changes. Finishing all sides will slow it down but never stop it. The first pic shows all of one board and a bit of the second where it looks like you alternated growth rings. But the boards look very wide and they are flat sawn. They will warp as the humidity changes. You should get the book "Understanding Wood". It may also be the boards were surfaced before they were sufficiently dry.

    also, if the warp is a lot, and you hold the top flat with clips the top will crack as the warp force is very strong.

  4. #4
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    The wood came from my husband’s family farm. It was cut about 30-40 years ago and has been stored in a barn since that time. So it is dry. But, I do agree with the comment about the wide boards. I probably should have ripped them into smaller pieces and actually I thought about doing it. But sadly, I didn’t. I have learned a great deal with this project and it is still continuing. BIG SIGH..........

  5. #5
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    If it sat on your work bench without any air space between the bench and the walnut then I think Mel’s approach will be just best bet.
    Forcing the wood into a shape it doesn’t want to be is futile.
    The exception is a good ridged base that holds it for years and years.
    Good Luck
    Aj

  6. #6
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    Quote Originally Posted by Gail Ludwig View Post
    The wood came from my husband’s family farm. It was cut about 30-40 years ago and has been stored in a barn since that time. So it is dry. But, I do agree with the comment about the wide boards. I probably should have ripped them into smaller pieces and actually I thought about doing it. But sadly, I didn’t. I have learned a great deal with this project and it is still continuing. BIG SIGH..........
    Sitting in a barn does not mean it's dry. What it means is that it has reached equilibrium in the barn's conditions. Seasonal changes don't mean it will warp if all surfaces are exposed equally to the air. If it is laying down on something and the air only gets to one side, then the exposed side is what changes faster and you get the warp. First I would just stand it up and let air get all around it. You furnace is surely running some days now, so everything is drying out and shrinking. It'll be changing again with the lower humidity.

  7. #7
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    Seems we all get to learn this lesson for ourselves despite reading about others troubles ;-) I now make tops and other large panels just prior to finishing or assembling or both. There are plenty of for and against arguments for and against breadboards as being functional elements with today's lumber handling and glue modernization. I'm still for 'em out of habit and an affinity for the look.

    I assume since your "breadboards" pull out to accept leaves they are not actually functional as breadboards. Given that you let an assembly lay about for a period of time, functional breadboard ends may or may not have saved you. A common failure is to glue up a large panel early and then leave it standing on one edge or worse, laying flat on a surface for an extended time. The wood does what it does and then we find ourselves here in this discussion.

    It is possible that if the piece had been stored on stickers allowing equal air travel all around the material that it would have done better. No guarantees of course. The lesson to be carried forward is to make large panels when you are ready for them and then execute as planned. Deviating from this process requires that you accept that you may have to "make another one". Determining which is more important at the time of interruption is a fluid process. Good luck
    "A hen is only an egg's way of making another egg".


    – Samuel Butler

  8. #8
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    Yep, clamping it flat will do nothing but temporarily hold it flat until you take the cauls off. 1/4" cup over what width? I assume 36-42" if its a dining table. How thick? If its 1/4" over 48" and the top is 1.25" or so, id imagine you can pull that flat to the base. Allow for movement yada yada yada, but you can torque it down. If its thicker and narrower, you might want to enter the field of woodworking dark magic and do like Mel suggests. Its shocking how much you can manipulate wood by introducing moisture to one face and drying the other face. Ive had to do this 2-3 times in my life and ive pulled 3/4" cups out of 60" lengths etc. Overdo it and it will swing the other way on you.

  9. #9
    I think you can pull 1/4 out of it when you fasten it to the base. I would start applying finish. Leaving it unfinished is not going to help it and I doubt clamping it as you apparently have will help either. As long as it sets unfinished it is going to continue to either dry or get wetter depending on the moisture level in the wood and the moisture in the room it is in. When the moisture moves around the top will tend to also.

    I would not finish the bottom and then wait awhile and finish the top. When you do that you greatly retard the mositure movement from the bottom but not the top. That is a very good way to get it moving. Much better to wipe a coat on the top one day, the bottom the next, etc.. Or if you use water borne, you can do 3 coats in a day. But I would probably use oil based on walnut so it would be a coat a day. But other than the hassle of flipping it no reason you can't do side 1 the first day, side 2 the second, etc, right?

    I understand it is challenging to see your nice flat top cup but I don't think you will see it in the finished table.

  10. #10
    Patrick,thanks for the kind word, and agreement on treatments helps an Op go forward with confidence.

  11. #11
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    A 1/4" is not terrible and it may pull into flat using Mel's solution and some type of base frame to pull it the rest of the way.
    Unfortunately, Glenn's solution may be your final solution, which is to either make another top, or remake the existing top.
    I would highly doubt that there is a wood worker alive, that has not been exactly where you're at. It seems we all think we'll get by the nature of wood, until it gives us a good enough spanking. Then we change.
    Give Mel's method a few weeks and if the end result is not acceptable to you, rip the existing top down the glue lines, re-mill the wood and do a second glue up.
    "The first thing you need to know, will likely be the last thing you learn." (Unknown)

  12. #12
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    Just curious but which way was it warped when you went to the basement? Was the cup downward? Unless you run a dehumidifier it probably gained moisture on the exposed side. Which would make it swell/expand on that side. No expert here but if it were flat when it it was first assembled then it should return to that after everything equalizes. Then get the finish on all of it. I learned the hard way on a much smaller piece about would movement. I put a edge across the cross grain of a bench seat. Same thing it sat for a few weeks and it had a significant warp to it. The side that was held by the edge board couldn't expand. i removed it and after a few more weeks it was flat again. I think yours will flatten once equalized. Good luck.

  13. #13
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    Well, I took the cauls off today and it did look like they helped a bit. I went ahead and put one coat of wipe on poly on the top and when dried, I flipped it and put a coat on the other side. I will try to get a couple of coats on each side tomorrow and then attach it to the bottom. I plan to put quite a few coats of poly on the top, so this will continue for a few days. So stay tuned. I appreciate all the advice you have given me. And I learned a valuable lesson— don’t let flat panels lie about for any length of time. Finally, I have to get this table finished because it has mucked up our living room for a few weeks. My husband is getting pissed!!! HaHa—many of you guys always talk about how your wives yell about the messes you make. Well, in our house it is exactly the opposite!!!

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