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  1. #1
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    Default How to flatten bowed huon pine boards?

    A few years ago I bought a board of huon pine with some birdseye in it. It has been laid flat on a floor in its original black plastic wrapping for that time, opened one end. The dimensions are 180 W x 600L x 10mm thick

    Dug the board out today to use, and found the board had bowed lengthwise, like it has been standing at an angle against a wall for that time If I try to sit it flat on the floor, it looks a bit like the Sydney Harbour Bridge - actually, the under side of the board is only about 20mm 6mm off the floor. No sign of any twisting or cupping across the width of the board. If I press hard enough, it will flatten to the floor without any damage.

    Does anyone know of any old craftsman's trick that I could use to permanently flatten it, like wetting the concave side and putting weights on it, whatever?
    regards,

    Dengy

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  3. #2
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    Turn it over sit it on something like blocks either end and weight like you have said. Wetting it won't do much unless its bone dry being and oily wood. Throw it on the back lawn in the sun upside down but in this heat keep close eye on it.

  4. #3
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    Thanks for this, wheeling around. I have edited my original post - it was only bowed 6mm - seemed much more when held agaisnt a straight edge and looking into a light.
    Which side do I wet and put on the ground - the under side which is concave, or the upper side which is convex? Which side faces the sun? Put more simply, do I try to weigh the top of the arch down, or do I lie it curved upwards and weigh the ends down
    regards,

    Dengy

  5. #4
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    When wood has cupped it is clear that the wood on one surface (outer curve) has expanded or the wood on the inner suface (cupped or inner curve) has shrunk. The idea is to make the wood on the inner surface expand so the board flattens out. Usually you wet the grass first, not the wood, then you place it hollow side down on the wet grass in the sun. The heat induces the wet grass to emit water vapour which is taken up by the wood. The wood swells and expands, so making that surface expand to match the upper surface and thus a straight board.

    The best result I have had with the technique are when one surface is sealed and the other not sealed. However, it is worth a try with the Huon. If you get it straight you will need to look haw you store it or else seal it. Having strored it in plastic is there any chance that one side got wet (say the underside) because if it did you could possibly flatten it just by racking with stickers to get even airflow.


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  6. #5
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    I don't think at 10mm thick and that length, that 6mm is a big worry. I'd only worry about it after you've decided what your going to do with it. What are you going to do with it ?

  7. #6
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    thanks for your help, people.

    The HP timber is was going to be a 250 L x 100mm H side of an open box, after it was machined to about 7mm thick. There is not going to be any lid, and the timber will be held in position along its length by being glued to a 4 mm thick plywood base via a rebate in the HP
    regards,

    Dengy

  8. #7
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    Quote Originally Posted by Dengue View Post
    thanks for your help, people.

    The HP timber is was going to be a 250 L x 100mm H side of an open box, after it was machined to about 7mm thick. There is not going to be any lid, and the timber will be held in position along its length by being glued to a 4 mm thick plywood base via a rebate in the HP
    my thoughts on it based on what you've said.

    don't bother trying to straighten the board. Dock your pieces slightly over length,,,,and each piece will have less cupping ... (based on that 6mm you mentioned) .. face/edge/thickness each piece and you'll probably have enough meat for that final 7mm thickness. And at 7mm thick it will have pretty good flex anyway that it won't be a problem.

    In my opinion, don't attempt to straighten a board with moisture/heat if you don't have to. It might be cupped but at least its more stable. There's no guarantee that a heating/moisture attempt will work as well. You maybe able to straighten the board this way initially, but find after its stabilised again (dried out) it cups up again.

    Just an opinion. not an expert on cupping huon pine. 2 cents worth.

  9. #8
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    Quote Originally Posted by apricotripper View Post
    my thoughts on it based on what you've said.

    don't bother trying to straighten the board. Dock your pieces slightly over length,,,,and each piece will have less cupping ... (based on that 6mm you mentioned) .. face/edge/thickness each piece and you'll probably have enough meat for that final 7mm thickness. And at 7mm thick it will have pretty good flex anyway that it won't be a problem.

    In my opinion, don't attempt to straighten a board with moisture/heat if you don't have to. It might be cupped but at least its more stable. There's no guarantee that a heating/moisture attempt will work as well. You maybe able to straighten the board this way initially, but find after its stabilised again (dried out) it cups up again.

    Just an opinion. not an expert on cupping huon pine. 2 cents worth.


    I agree with this. Plus, remember that you're going to finish it with something. That will also cause the wood (being very thin) to bow slightly and it may straighten itself. I was building shelves once. The backing was thin - 3 mm plywood. It was very badly warped, but after applying a coat of clear finish on the concaved side first, to my surprise it flattened itself when the finish dried.
    Good luck with that.

  10. #9
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    If I understand the OP correctly, the board is not cupped it is bent. Doing the water trick or sitting on wet ground with weight will not straighten the bend and will probably cup it. As others have said, leave it alone and use it as it is.
    “We often contradict an opinion for no other reason
    than that we do not like the tone in which it is expressed.”

    Friedrich Nietzsche


  11. #10
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    I agree with Marc. It sounds like it has not cupped (side to side) but bent or distorted lengthwise. It should easily disappear once you use it as planned. My earlier post was on the assumption it was cupped.


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  12. #11
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    Thanks for the advice, everyone. I will proceed with cutting it up and then dressing to eliminate the bowing in the shorter lengths. Hopefully I will get 7mm thick boards out of the bowed 10mm boards. Will post pics of the final box.

    With respect to the terminology of timber defects used, this site by David's Timber in Victoria shows the terms I have used.
    regards,

    Dengy

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