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Thread: Need help with steam bending

  1. #1

    Need help with steam bending

    I purchased some 5/4 knotty alder about 4-6 weeks ago. While sitting in my garage it has twisted on me really bad. The pieces are roughly 6" wide by 10 feet long and some have over 1/2" of twist. I was hoping to get 1-1/8 finished thickness out of these boards. If I mill this out with the jointer and planer I won't even be able to get a 3/4" thick board, much less 1-1/8". The alder was kiln dried. I've read that this means no amount of steaming will work for bending or in my case un-twisting. However, I have proved this statement to be false as I've had some degree of success trying to steam and un-twist the board back straight. However, I'm getting a lot of spring back. Can anyone suggest a steam duration and technique? How far past straight do I go with my mold to get the thing to spring back straight. Also, after I remove the steam, and twist it back straight, how long does it need to sit in the form before I take it out and hope that it's straight? I'm in Denver, super low humidity here so wet boards dry really fast. I'm not looking for perfection here. Just straight enough to be able to take to the jointer/planer and not have to remove more than 1/16" or maybe 3/32".

  2. #2
    A guy can dream, can't he?

    Getting that much twist out of a board isn't likely to happen no matter what.
    Fair winds and following seas,
    Jim Waldron

  3. #3
    Join Date
    Apr 2017
    Location
    Michigan
    Posts
    348
    1. You must become the expert in springback in this particular situation.

    2. Depending on how you will be using the wood it may not be necessary to get it flat. You can forget the jointer and just plane it to a twisted but consistent thickness and work with it.

  4. #4
    Join Date
    Aug 2010
    Location
    Scarborough(part of Toronto|) Ontario
    Posts
    190
    Maybe this booklet from Lee Valley might be of some help to you. "http://www.leevalley.com/en/wood/page.aspx?p=31161&cat=1,46096,45867
    With any steam bending I have done, I found the spring back to be very unpredictable. I make the form so it overbends the board. The amount is a guess. I most cases it is not critical because both ends are restricted from moving in the final product.
    You keep the board or whatever in the form until it has cooled to room temperature.
    Cheers,

    Tim

  5. #5
    Join Date
    Feb 2003
    Location
    McKinney, TX
    Posts
    1,565
    Do you need the full 10’? Normally rough cut an inch over needed length then joint and plane
    Steve Jenkins, McKinney, TX. 469 742-9694
    Always use the word "impossible" with extreme caution

  6. #6
    Knotty? Kiln dried?

    If I had to do this, I'd not overbend it. I'd soak it for a day, then steam it, then clamp it flat. This is not to say I think it's a worthwhile effort.
    You'll be no worse off than you are today, at least, though.
    Last edited by Prashun Patel; 09-18-2018 at 10:43 PM.

  7. #7
    Join Date
    Jun 2013
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    Here is an analogy; It is easy to take a straight wire and bend it into a paper clip, but once it’s bent into a paper clip it’s near impossible to get it back to a straight wire again. Much the same with wood- in order to straighten the board, it will take the exact amount of bend in exactly the right places, and with spring back that is difficult to figure out.

    I have straightened bent guitar necks, but it sounds like your board has a few twists and is much longer.

  8. #8
    In traditional boat building, wooden planks are formed around frames and fastened in place to make up the shape of the hull. In the case of some designs, it is necessary to also twist the planks to propely conform to the shape of the frames. Depending on size, shape and specific materials used, it is not uncommonly desirable to steam the planks to aid in the forming. In some cases, steaming is essential. When in place, the plank is fastened in place, typically with screws or, in small craft, with rivets.

    When the fastenings are pulled, even after years of service, there will be springback. Not all the way to a straight timber, but typically quite a lot. And if that plank is to be rehung on the frames, it will take substantial force to bend it back into place.

    More recently, it has become common to laminate hulls of multiple plies of sliced or sawn veneers, 1/8" to 1/4" or sometimes more in thickness. These are formed (i.e. bent and twisted as needed) in place and bonded, typically with an epoxy adhesive formulation. The veneer skins are often bonded over comparably laminated frames. Along the way, it was found that springback is somewhat predictable; with 8 or more plies of veneer in a laminate, springback is so slight as to be a non-factor; two plies will have dramatic sringback. The amount of springback will vary somewhat with the species of wood, but is largely independent of the thickness of the plies.

    Unless the OP finds a way to slice his piece into 8 or more plies which can then be laminated on a flat form, there is no realistic way to attain the straight form he desires.

    If he has a better idea than I know of, I would never dream of dissuading him from trying. Bon chance.
    Fair winds and following seas,
    Jim Waldron

  9. #9
    Often for me - it takes several goís at it.. Always clamp it to a form and let it dry a couple days. Soak, steam, then clamp... Undo it a couple days later to see how it came out. Lather rinse repeat till it settles in enough for you. Then stack it under a big pile of lumber for a while.

    Another trick I stumbled across is to chunk it outside in the rain/sleet/snow for a season and just let it relax in the elements. It will settle into wherever itís natural equilibrium is - and then you can go from there to sort it out.

    Realize though - cranky cantankerous wood is likely to be that way for a LONG time... And so if you need it to be flat and not warped all over the place - get different wood.

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