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  1. #1
    Join Date
    Jan 2007
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    Default Jarrah table top - now bowed

    I'm hoping some advice can be offered on why the table top i have made has now bowed - along with any solutions!! The top comprises 6 Jarrah boards spaced intermittently with pine strips. The Jarrah is in the region of 150 x 25, the pine strips approx 25 x 25. It does not appear to originate between the two woods and thus i don't expect that it has anything to do with the varying strength of the two types. All is jointed with biscuit joints & the piece has always been supported appropriately from underneath. The bowing is clearly evident, and is probably a deflection of 1 inch up at either side.
    <O</O
    <O</O

    See attached photo’s for before & after pics of the top, along with a couple of the base - still a work in progress. I hope someone can provide some advice. . . .<O</O

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  3. #2
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    Default

    Silly question, perhaps, but is the underside of the table properly sealed? If not, it could be picking up moisture on that side and swelling.
    Also, your Jarrah boards appear to be back sawn and the grain is all oriented the same way, at least in the right of pic 3. A possible fix would be to run half-depth kerf-cuts on the underside lengthwise and then screw it to some strong, straight boards.
    Cheers,
    Craig

  4. #3
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    Silly question perhaps but have you sealed the top and bottom faces of the table top in similar way?
    Cheers

    TEEJAY

    There is a very fine line between "hobby" and "mental illness"

    (Man was born to hunt and kill)

  5. #4
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    Quote Originally Posted by Exador View Post
    Silly question, perhaps, but is the underside of the table properly sealed? If not, it could be picking up moisture on that side and swelling.
    Also, your Jarrah boards appear to be back sawn and the grain is all oriented the same way, at least in the right of pic 3. A possible fix would be to run half-depth kerf-cuts on the underside lengthwise and then screw it to some strong, straight boards.
    Hey come on Craig - I bet I wrote this first - had to answer a kid at the front door before I pressed submit
    Cheers

    TEEJAY

    There is a very fine line between "hobby" and "mental illness"

    (Man was born to hunt and kill)

  6. #5
    Join Date
    Aug 2002
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    Sydney, NSW, Australia
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    Default

    How do you attach the top? With buttons or some other method that allows the wood to move?

  7. #6
    Join Date
    May 2007
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    wagga wagga
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    Default

    Had the exact same thing happen to me a couple of days ago ! had my table top sitting on my work bench good side up oiled & came back the next day & the middle was sitting up about 10mm so i flipped it u/d & oiled the bottom & left it for a couple of days & its now gone in the other direction & resembles your top ( so flipped it again ) if it does not come good i will put it bowed side up in the sun to draw some moisture & cross my fingers.

    bloody wood ......crazy stuff

  8. #7
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    Quote Originally Posted by TEEJAY View Post
    Hey come on Craig - I bet I wrote this first - had to answer a kid at the front door before I pressed submit
    I'm claiming copyright.
    Cheers,
    Craig

  9. #8
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    Turn the table top up side down and leave it for a while??

    I always build the top last so I can attach it to the base right away.
    Visit my website at www.myWoodwork.com.au

  10. #9
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    Quote Originally Posted by Wongo View Post
    Turn the table top up side down and leave it for a while??

    I always build the top last so I can attach it to the base right away.
    But wouldn't that mean that the legs would come up off the floor
    woody U.K.

    "Common looking people are the best in the world: that is the reason the Lord makes so many of them." ~ Abraham Lincoln

  11. #10
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    As Craig has said, all the grain in the boards seem to be oriented the same way. This isn't so much of a problem if 1. the table top is small 2. the timber is KD and 3. if you seal it both sides.

    But even then, you've got to expect a single "board" of any width to cup. By gluing up "same orientation" boards, the pieces become one. So the wider the top, the greater the shrinkage on each side of each face, which gives us the cupping.

    Can I suggest some unpalatable solutions?

    First, rip the table on the glue line. Then square the edges to each face and reglue, preferably without the strips. I know they add contrast, but they will certainly move at a different rate to te Jarrah.

    And, because it seems the Jarrah isn't KD or perhaps even dry seasoned, orient the boards one up, the other down. That way, the top will ripple rather than cup, but it's managable. Suggest you check the moisture level too.

    Of course, seal all over.

    I'd be re-jointing the top as suggested and fixing it to the top unsealed for a while and see what happens.

    It certainly seems strange that the cupping occurred this time of the year when humidity is relatively low. Where are you from?

    If you are determined to leave the top as is, suggest you strip off the finish, wet down thoroughly with water, place weights on the top and let it move back to original condition. Then, fix firm in the middle of the top and see if you can defy nature!

    I also didn't know Jarrah moved so much on the tangential plane. Something learned every day.

    Hope this helps. Nice looking table but for your problem!

    Jefferson

  12. #11
    Join Date
    Jan 2007
    Location
    Melbourne
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    17

    Default

    Oi choi oi!
    Thanks for the replies.
    The bottom is not sealed/coated at all - i'm certainly learning a lot from this project! What is the likelihood that things will come back to "normal" once done? The top is polished so should i be polishing the bottom also, or a more simple seal method?

    It hasn't as yet been attached to the base - still working on the base. If i manage to flatten and attach (once the base is ready), what are the chances it would simply pull through any attachments in its effort to re-curl?

    I don't like the thought of re-cutting, joining, polishing etc (will if i have to though) - especially if there is a chance this will happen again

    I'll have to plead ignorance on the "orientation" of the grain. How can i tell which way it is orientated?

  13. #12
    Join Date
    Apr 2006
    Location
    Broken Hill
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    Default Orientation

    Hi vaughn

    "I'll have to plead ignorance on the "orientation" of the grain. How can i tell which way it is orientated?"...

    look at the end grain,,, see how the grain runs - convex or concave...
    if you join the boards with all the end grain concave "u" shaped - then you get a curve in the table top like yours... Join them all convex "n" shaped and you get the opposite - a hump in the middle...
    So you've to alternate - one board with the grain oriented convex "n" joined to the next board with the grain oriented concave "u", next to convex "n" then concave "u" etc etc...
    That way, as it expands and contracts you get a ripple effect rather than the gross effect of a bow...

    edit: However, I think that not sealing the underside is the biggest culprit here...
    Jedo
    When all the world said I couldn't do it - they were right...

  14. #13
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    I would stick it out in the sun upside down to draw the moisture from the bottom until straight or very close to it and then seal the bottom and your problem should be pretty much fixed.
    Check my facebook:rhbtimber

  15. #14
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    Default

    I had a similar problem with a jarrah table top, despite its being sealed both sides. I cured the problem by screwing (using slotted holes to allow for wood movement) two heavy cleats to the underside to straighten it. It worked fine, and did not require any of the more drastic solutions sugested above.

    Rocker

  16. #15
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    Quote Originally Posted by Rocker View Post
    I had a similar problem with a jarrah table top, despite its being sealed both sides. I cured the problem by screwing (using slotted holes to allow for wood movement) two heavy cleats to the underside to straighten it. It worked fine, and did not require any of the more drastic solutions sugested above.

    Rocker
    Essentially, that's what i'd do. the kerf cuts are just to take the compressive strength out of the back of the board so that battens will hold it down more easily. It's an old trick used on drawing boards, even those that are laminated.
    Cheers,
    Craig

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