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Thread: Flattening a cupped board

  1. #16
    Join Date
    Dec 2003
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    SF Bay Area, CA
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    15,332
    Martin...I am from Colorado but have lived in California since 1998 so I enjoyed the first Super Bowl win by the Broncos while still in town but watched the second SB win from here in California....

    You might rent some time with a pro woodshop, Martin, that has a wide enough belt sander and just go for it. Otherwise, you could get quite a work out with an appropriate hand plane to shave down either the sides or the middle.

    Sounds like a very nice piece...could you post some pics of it?
    Wood: a fickle medium....

    Did you know SMC is user supported? Please help.

  2. #17
    Join Date
    Feb 2003
    Location
    McKinney, TX
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    Hey Martin isn't about time for a road trip to Dallas? like maybe for the 23rd?.
    I have a solid oak dining table that is about 42x96 that was outside and rained on for a summer. It's not mine but I'm trying to flatten it for a client. I got it to flatten by putting the top concave face up and keeping wet towels on it for about three days in the shop. this was without removing the finish. it flattened out but when it re-dried it curved right back again. I've decided I need to try Todd's method. Steve
    Steve Jenkins, McKinney, TX. 469 742-9694
    Always use the word "impossible" with extreme caution

  3. #18
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    Dec 2003
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    SF Bay Area, CA
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    Steve,

    I wonder if you remove the finish if it will hold? Perhaps some clamps/weight might help??
    Wood: a fickle medium....

    Did you know SMC is user supported? Please help.

  4. #19
    Hey Steve, I would love to come to Dallas for the BBQ and see everyone. Its been a long time. I would also like to come poke around your shop and visit with the master. Maybe around Christmas. My wife is from McKinney.

    Did you hold the top flat while it dried? I wonder if that would help. The cup is too much for a wide belt sander. Probably 1" - 1 1/4" over the length of the plank.
    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

  5. #20
    Join Date
    Dec 2003
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    That burl is a pretzel, Martin!! I think the slow route is a good one to take for your situation. Perhaps if you can get it flatter the slow route (and not necessarily flat) you could then sand/plane it flatter or perhaps rip it in half and resaw it into veneers. Fun stuff to play with....
    Wood: a fickle medium....

    Did you know SMC is user supported? Please help.

  6. #21
    Join Date
    Jan 2004
    Location
    Tacoma, Wa
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    222
    I LOVE THIS SITE!!! Thanks Todd...what a timely post....I have a need for this very info...I was gonna rip down a board to fit the 6" jointer, remove the cup and then reglue but I'll try this technique first...Thanks.

    Greg

  7. #22
    Todd does it again!! Great tip for sure and it will help many of us. I had one like that happen once on an Oak panel I had made. I ripped and re-glued it in alternating patterns...your idea woulda been much easier!!

  8. #23
    This is an extremely old post, but I just had to revive it. This technique worked marvelously for me on a blanket chest I'm making now. Thanks, Todd...

  9. Quote Originally Posted by Todd Burch View Post
    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, Thank you for the useful post! Any idea if I could make this work in reverse? My tabletop is cupped in the opposite way, as in the concave side is the bottom of the table and convex is the top. I"m trying to picture it in my mind...could I make relief cuts in the bottom could I force it to flatten out? In theory it seems like it might work? wondering as to whether or not You've tried it this way or not. Thanks in advance! -Nick

  10. #25
    Wow, this thread started 14 years ago lol.

  11. #26
    Join Date
    Mar 2012
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    Napa Valley, CA
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    916
    Quote Originally Posted by nicholas guenther View Post
    Todd, Thank you for the useful post! Any idea if I could make this work in reverse?... -Nick
    Nick-- I don't know if Todd is around any more but the concept should work on your table top. I would make the kerfs about 2/3 the thickness of the top.

  12. Thank you for the feedback Jerry!

  13. #28
    the old guys did this on furniture when they built it. If I looked at any top made by my favourite old guy there were kerfs under the table top. Even an end table the top had a number of kerfs in it, its called breaking the back. Inserting wood here a way to hopefully solve a problem. They were trained how to avoid them.

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