Has anyone tried . . .

Discussion in 'Materials' started by ancient kayaker, May 22, 2013.

  1. ancient kayaker
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    ancient kayaker aka Terry Haines

    - bendable hardwood at this site http://www.puretimber.com/ ?

    I understand it's wet hardwood that has been compressed along the grain so it will stretch along the outside of the curve as well as compressing along the inside. Extreme bends are claimed. It becomes stable and holds the shape when dried.

    Not sure what the drying time is or how stable it is if it gets wet again . . .
     
  2. daiquiri
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    daiquiri Engineering and Design

    Wow! Looks great! :)

    I understand that it uses the same principle as steam bending, plus the external metal skin which carries over the tension stress which would otherwise break the wood fibers during the bending phase. Ever done the trick of tying a cigarette into a knot? This looks like the same principle. Very smart indeed. It opens a whole range of creative possibilities for woodworkers.
    Thanks for the link.
     
  3. gonzo
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    gonzo Senior Member

    Tying a cigarette in a knot? Wow, I hadn't heard of that one.
     
  4. daiquiri
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    daiquiri Engineering and Design

    It's one old trick, did it when I was a kid.
    You actually cannot normally tie a cigarette in a knot - it will break if you try. But... if you tightly wrap it in a transparent (so you can see what happens inside) plastic film, like the one used for cooking bags, you will easily tie the cigarette without breaking it. The plastic film will take over all the tension stress which would otherwise try to pass through the cigarette paper, hence the cigarette won't snap. ;)
    Cheers
     
  5. SamSam
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    SamSam Senior Member

  6. ancient kayaker
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    ancient kayaker aka Terry Haines

    That certainly seems somewhat safer than bull-fighting.

    I thought the phrase "the dance of the steam bender" conveyed a great deal of hidden meaning . . . it seems that laminating rules, but the glue drools.
     
  7. rwatson
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    rwatson Senior Member

    Looking closely, you may have identified the technique that the PureTimber guys use.
     
  8. Landlubber
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    Landlubber Senior Member

    Interseting articles fellas, ta.
     
  9. messabout
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    messabout Senior Member

    Dynamite Payson told us about using ammonia a long time ago. He used household ammonia for many of his model projects. For full sized bending, the volume of all that nasty ammonia would become scary.

    I'm inclined to laminate but AK is right in that ....laminate rules but epoxy drools.
     
  10. DCockey
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    DCockey Senior Member

    I talked to Pure Timber several years ago about their "Cold-Bend" wood for a non-marine application and purchased a sample, but haven't used it. No ammonia is used in producing it. The wood is shipped straight wrapped in plastic, and the user saws it and bends it as needed.

    From the Pure Timber website (bolding added): http://www.puretimber.com/how-its-made/

    Cold-Bend™ hardwood undergoes extreme physical, longitudinal thermo-mechanical compression. There is no chemical treatment, or glues used in the process. Cold-Bend™ hardwood is solid hardwood that has been selected and milled to yield clear lumber. It is carefully controlled for moisture content. Cold-Bend™ hardwood is not modified in any way except for the extreme compression and the careful quality selection and moisture control required for its extreme bending qualities.

    Wood used for compression must be clear and straight grained - essentially veneer quality temperate hardwoods (i.e. beech, ash, oaks, cherry, maple, walnut) . Softwoods and most exotics do not work in this process. After sawing from the log, the green, wet boards are partially dried over a period of a few months, then sawn and planed to the required dimensions.

    The patented and trademarked Cold-Bend™ hardwood process begins by steaming the planks under pressure in a long autoclave. The plasticized boards are then placed in the compression chamber of the Cold-Bend™ hardwood press, which compresses it lengthwise to about 75 to 85 percent of its original length, while maintaining the other dimensions. The wood is altered at the cellular level. You can think of the normally rigid cell walls as sliding into or folding over on themselves. Imagine a drinking straw, and a hospital straw, and you will get an idea of the difference between hardwood and compressed hardwood. You may also think of the compression as producing a bellows effect in the cell walls.

    Once removed from the press, the wood returns to about 10 percent of its original, trimmed length during a process called "Compression Resting". It is immediately set into a second press where the forces are allowed to equalize throughout the compressed planks. After compression and resting, the wood retains amazing flexibility, as long as it is kept moist, making it suitable for bending cold, by hand. The compression allows the wood to both stretch on the outside of the curve (something wood can't otherwise do) and further compress on the inside of the curve without backing straps, heat or steam. The wood is flexible until dried, so it can be bent onto or over a fixture while wet, then dried to fix the shape. The dried wood is rigid, and is identical to the original wood, except that by now it has probably taken on some cool new shape. About 5 to 10% of the original strength of the wood may be lost, insignificant in most applications, and usually better than other shaping methods like steam, lamination and sawing curves.
     
  11. daiquiri
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    daiquiri Engineering and Design

    Very interesting David, thanks. I would have expected a significant loss of strength after all that manipulation, but evidently I was wrong. Now the question is - is this process suitable for marine constructions? After all that bending, can they certify a minimum guaranteed wood strength for scantling purposes?
     
  12. ancient kayaker
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    ancient kayaker aka Terry Haines

    An awesome process which explains the awesome price . . .
     
  13. upchurchmr
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    upchurchmr Senior Member

    Strength might be not so bad, but I wonder how it stands up to repeated loads. Normally wood is really good for that, but this has been predamaged.
     
  14. Petros
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    Petros Senior Member

    I would think it is not suitable for marine applications at all. I am also highly skeptical of the 10 percent loss of strength. I would think that if it becomes wet, like for use in a boat hull, it would loose a lot more than 10 percent of its strength. the structure of the wood is already crushed and damaged even before it has any load on it.

    I notice that no where on their page do they show it in a structural application. I think it is intended for non-structural applications like custom window trim, curved stair rails, etc.
     

  15. keith66
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    keith66 Senior Member

    A friend who works in a joinery factory recently gave me a couple of samples of a similar product, http://www.bendywood.info/index.php?lang=english, sample was beech about 1/2" square & it could literally be tied into a knot cold.
    My first thought was it could be ideal for use in steamed timber replacement but further reading shows that its not recomended for damp conditions.
     
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