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Thread: Flattening a cupped board

  1. #1
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    Flattening a cupped board

    If a board, counter top or tabletop won't stay flat and wants to cup, and I need it flat on its own merit, I'll kerf the board lengthwise on my tablesaw with the grain, on the bottom or backside, push/clamp it down flat, and glue in a strip of matching wood. I've attached a photo-essay of the process. While I show the kerf running all the way out the end of the wood for illustration purposes, on pieces that the end-grain will show, I stop short of the end so that you can not see the glued in strip(s).

    I use this technique to flatten both lumber and plywood. If I'm flattening plywood, like for a counter top, I won't go through the hassle of glueing in a wedged spline, 'cuz you'll never see it. The technique is the same technique as kerf-bending, but the objective and results are just opposite (curved to flat instead of flat to curved).

    I'll make the splines rectangular, the same width as the fattest part of the wedge, and then either block plane or sand the spline to fit. It can be full length or pieced in.

    Depending on the piece and the amount of cup, I will choose a depth of cut for the kerf. For a large solid wood tabletop, I will kerf only as far as I feel I need to to get the cup out. On utility items, I generally kerf deeper for speed's sake.

    Todd

    (Drawings done in Sketchup!)

    (How many people wanna put odds on this technique showing up in a woodworking rag within the next 2 months? )
    Attached Images Attached Images

  2. #2
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    Feb 2003
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    Gastonia, NC
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    Todd,

    Quote Originally Posted by Todd Burch
    If a board, counter top or tabletop won't stay flat and wants to cup, and I need it flat on its own merit, I'll kerf the board lengthwise on my tablesaw with the grain, on the bottom or backside, push/clamp it down flat, and glue in a strip of matching wood. I've attached a photo-essay of the process. While I show the kerf running all the way out the end of the wood for illustration purposes, on pieces that the end-grain will show, I stop short of the end so that you can not see the glued in strip(s).

    I use this technique to flatten both lumber and plywood. If I'm flattening plywood, like for a counter top, I won't go through the hassle of glueing in a wedged spline, 'cuz you'll never see it. The technique is the same technique as kerf-bending, but the objective and results are just opposite (curved to flat instead of flat to curved).

    I'll make the splines rectangular, the same width as the fattest part of the wedge, and then either block plane or sand the spline to fit. It can be full length or pieced in.

    Depending on the piece and the amount of cup, I will choose a depth of cut for the kerf. For a large solid wood tabletop, I will kerf only as far as I feel I need to to get the cup out. On utility items, I generally kerf deeper for speed's sake.

    Todd

    (Drawings done in Sketchup!)

    (How many people wanna put odds on this technique showing up in a woodworking rag within the next 2 months? )
    Thanks! Now that is information worth keeping. Do you use a formula for depth of cut or trial and error? Also, when you need to stop short of the ends, do you just stop your table saw blade short or do you use a router, etc? Thanks for sharing, and have a great Christmas.
    Be Blessed!

  3. #3
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    Chris,

    No formula, just trial and error, until that turned into experience! The way I showed the cup in this illustration would be difficult to cut on the tablesaw - since it's cupped! In this case, I would use a circular saw (now that I have a Festool). A router would work, but that would be a lot of traveling with a 1/8" router bit. I break all my 1/8" bits on first use typically. (The board I showed is 40" wide and 10' long - to scale). When I have to bend a board flat and the kerf wedges closed instead of wedging open (like I showed), I just make the spline rectangluar in section (simpler) and use glue to fill the gap down in the wood where it is hidden and will never be seen. Todd.

  4. #4
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    Nice...thanks for the tip, Todd. Are you preparing for that chunk 'o bubinga, maybe???

    I need to start playing with my trial version of Sketch-up...interestingly, I think LOML will get a trial version, too!

    another Chris

  5. #5
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    Hey, now that IS information worth keeping! Todd, many thanks for that super helpful hint. You should send that in to one of the WW rags. I'd wager it would earn you a top spot and "prize"! The added exposure wouldn't hurt, either! Thanks again. Great info.

    HAPPY HO-HO!
    Cheers,
    John K. Miliunas

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  6. #6

    Cupped board

    Quote Originally Posted by Todd Burch
    If a board, counter top or tabletop won't stay flat and wants to cup, and I need it flat on its own merit, I'll kerf the board lengthwise on my tablesaw with the grain, on the bottom or backside, push/clamp it down flat, and glue in a strip of matching wood. I've attached a photo-essay of the process. While I show the kerf running all the way out the end of the wood for illustration purposes, on pieces that the end-grain will show, I stop short of the end so that you can not see the glued in strip(s).

    I use this technique to flatten both lumber and plywood. If I'm flattening plywood, like for a counter top, I won't go through the hassle of glueing in a wedged spline, 'cuz you'll never see it. The technique is the same technique as kerf-bending, but the objective and results are just opposite (curved to flat instead of flat to curved).

    I'll make the splines rectangular, the same width as the fattest part of the wedge, and then either block plane or sand the spline to fit. It can be full length or pieced in.

    Depending on the piece and the amount of cup, I will choose a depth of cut for the kerf. For a large solid wood tabletop, I will kerf only as far as I feel I need to to get the cup out. On utility items, I generally kerf deeper for speed's sake.

    Todd

    (Drawings done in Sketchup!)

    (How many people wanna put odds on this technique showing up in a woodworking rag within the next 2 months? )
    Todd,
    Excellent.... What is Sketch-up, I think I was using it incorrectly on french fries.. Where do you get that program
    Mark

    I went to the "sketchup" website...it looks good. Did you pay around $475?
    mark
    Last edited by Mark Singer; 12-25-2003 at 10:28 AM.

  7. #7
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    Yes, www.sketchup.com, Free to download an 8 hour trial, $475 to get a permanent key.
    Todd.

  8. #8
    Quote Originally Posted by Todd Burch
    Yes, www.sketchup.com, Free to download an 8 hour trial, $475 to get a permanent key.
    Todd.
    Todd,
    Do you like it? Merry Christmas!
    Mark

  9. #9
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    Do I like it?

    Do I like it?

    DO I LIKE IT???

    Does a bear poop in the woods? Is the Pope Catholic? Yes, I like it. (Understatement of the year award goes to Todd)


  10. #10

    Good Graphics!

    Quote Originally Posted by Todd Burch
    Do I like it?

    Do I like it?

    DO I LIKE IT???

    Does a bear poop in the woods? Is the Pope Catholic? Yes, I like it. (Understatement of the year award goes to Todd)


    Enjoy the day !!!!
    mark

  11. #11
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    Keith, please make into an article. Todd

  12. #12
    Todd, great tip.

    I am curious if you worry about the amount of moisture the glue adds to one side of the board. do you hold it flat for a certain amount of time? also have you ever tried it on burl? I have a large (30" x 60") maple burl 1" thick that I need to flatten. I have heard advice to lay it out in the sun over some damp grass. Any advice from the ranks of the creekers would be appreciated.
    Enjoy the journey,

    Martin


    ---------------
    Whatever is true, whatever is noble, whatever is right, whatever is pure, whatever is lovely, whatever is admirable --- if anything is excellent or praiseworthy --- think about such things. --- Paul of Tarsus

  13. #13
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    Sep 2003
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    Sunny California
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    Todd,

    Really cool idea which I will remember and use, ideal for the Festool saw too. Thanks for posting....

    Gene

  14. #14
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    Dec 2003
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    Martin,

    I would think the moisture unbalance to be a very temporary problem and not one that should cause the piece to curl back to where it was. MC should be back to "even" in a few days.

    Flattening something that thick (1") using moisture, heat, weight, and TIME takes some patience but it can be done. Todd's method is quite speedy. Also, I think the reverse of Todd's method could be done to the other side of the cup: only this time the kerf cut would close up: If someone made a router bit or even saw blade that would make a very steeply-angled V-cut, it should work to flatten the board. This way, you don't have to glue in extra wood...just close up the board on itself.
    Last edited by Chris Padilla; 10-06-2004 at 11:36 AM.
    Crown Molding: cut, cope, cuss, caulk, chill....

    Did you know SMC is user supported? Please help.

  15. #15
    Chris,

    Thanks for the reply. I am not sure how to get that flat. I dont want to cut into it because of the burl, but it would make a great desk top if I can flatten it. the moisture, pressure and time route may be the best.

    From your location it looks like you are in Colorado. Welcome to God's Country. The only better place is on the western slope of Colorado, but no prejudice here.
    Enjoy the journey,

    Martin


    ---------------
    Whatever is true, whatever is noble, whatever is right, whatever is pure, whatever is lovely, whatever is admirable --- if anything is excellent or praiseworthy --- think about such things. --- Paul of Tarsus

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