Text Resize

  • -A
  • +A
  • Q: Trouble joining boards for a table top

    I am joining 7 lengths of 6" wide walnut for a table top.  I am using dowels to keep the boards in line - just like the side table in season 3.  When I joined the first 3 boards they are cupping to form a "U" shape.  Will this go away once I do the glue up?  Am I doing something wrong? 


    I didn't joint or plane the boards myself.  I am wondering if the boards aren't straight and that is what is causing the issue.  The boads are flush up against one another but the whole collection of boards is warping?

    answer question

    All Answers

    Ed Pirnik writes:

    Hi Collin:

    I thought I'd add some materials to the lineup that might help regarding the milling of boards, as well as tabletop glue-ups. Hope these little nuggets are useful as well. Even if you're having someone else mill your boards, it's always a good idea to have a thorough understanding of the process:


    Rudiments of Tabletop Glue-Up
    Basic tips on milling and gluing multiple boards together for tabletops.

    Build a Shaker Nightstand Video Series
    Our Getting Started series on building a Shaker nightstand of American walnut covers basic milling techniques in episode 2 and a simple tabletop glue-up in episode 5.

    How to Mill Lumber
    Learn the basic steps involved in obtaining smooth, square, straight boards for furniture components.

    How to Use the Jointer Safely
    Best practices for safely and effectively using a jointer to obtain one flat, square face

    Asa Christiana writes: The are two main possibilities here. I don't think it is moisture content as the last guy suggests, and unless you have a moisture meter, you can't check any way. I think the key is that you didn't mill the boards yourself. My first guess is that the edges are not 90 degrees. Check them with a good square. You might be able to flip one or two of them to get the inaccuracies to cancel out. Or better, joint their edges with a machine or sharp hand plane. If you don't have those, head back to the place you got them and ask them to do it. But before attacking the edges, check each board individually with a straightedge to see if it is cupped. If it is, you won't be able to mill the edges accurately, and even if you do you'll get a warped glue up. If they are cupped, you've got the same options I outlined above. Successful woodworking is all about starting with straight, square, flat parts. Let me know how it works out for you.
    580 grandpa
    Clifford McGhghy writes:

    I don't think this will go away.  Cupping can be a wildcard.  Often time it is caused by planing the boards and removing all or most of the stock from one side of the board.  This actually makes one side of the board more moist than the other causing the problem.  Sometimes it just happens.  Wood can do that.  Was the wood climatized in your shop for awhile before working it?  This can cause problems if it was not.  Was it exposed to the sun.  This will cause cupping and twisting.  

    Begin by checking the moisture content of the boards.  This might give a clue.  Those boards need to be flat before you glue up.  Now is the time to correct the problem.  Then move on and you will have a better project and enjoy it more.   Wide boards tend to cup more than narrow boards.  Some people rip them into 3 to 4 inch wide strips and flip alternating boards.  This will cause one to pull upward while the adjoing board will pull downward.

    I wish you great success in your endeavor,