Flexible non-steamed wood for gunnels?

Discussion in 'Materials' started by sprit, Oct 19, 2013.

  1. PAR
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    PAR Yacht Designer/Builder

    It's really all about the heat. A heat gun can make some bends.
     
  2. Steve W
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    Steve W Senior Member

    While hot water works it is nowhere near as good as steaming. A simple steam box can be made with scrap wood or a couple of lengths of 4 inch pvc pipe joined together, all you need to produce steam is a camp stove or a propane turkey fryer, a steel 5 gal pail for the water or an old steel outboard fuel tank. Slope the steam box so as the steam condenses and becomes water again it flows back to the tank so your not having to top it up all the time, you can cap the end furthest from the tank but allow steam to escape from the other end, you dont want a pressure vessel. It may be old technology but is very satisfying to pull out a substantial hardwood piece and easily wrap it around just about anything. I would use white oak or something similar that you can get from a local sawmill, its best if it is still wet or air dried, hardwood would be best for your application and no need for glassing. This is a perfect job to gain the experience on.

    Steve.
     
  3. peter radclyffe
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    peter radclyffe Senior Member

    a hot water tank is more efficient than steaming
     
  4. Steve W
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    Steve W Senior Member

    Peter, please explain, im not saying you are right or wrong, i dont know. I dont profess to be an expert on steaming but I have used the technology from time to time over a 40 year boatbuilding career and never cease to be impressed with how well it works. The most recent was during a 2005 rebuild of a historic steam tug where all the 2.5 inch oak planking in the fwd sections required steaming. This was in an unheated building in the winter in upstate new york. Im trying to imagine the logistics of doing this with hot water, our steam box was outside covered in snow until it melted off when we fired up the steamer.
    I have also used the hot water and old towel method that. Par referenced on appropriate small jobs and even bundled up wood, weighted it down and thrown it in the river to soak, whatever works, but really, anyone can set up even a large steambox settup for peanuts.

    Steve.
     
  5. Petros
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    Petros Senior Member

    I have built about 12 skin on frame sea kayaks, most used steam bent ribs. I have built two or three different types of steam boxes. I usually use salvaged oak lumber or Alaska yellow cedar, I selectively rip my ribs from the better parts of the salvaged lumber. Using the old low cost lumber in a steamer, after I soak the wood for several days, I typically split about half of my ribs (not a big deal to make lots of extras). When I heat the wood in a water tub, not even to boiling but to just below boiling, I will split no ribs. boiling the wood allow for even using wood with small knots, grain runout, etc. without risk of splitting the wood. So I have found that boiling (or near boiling) the wood is much easier and much more tolerant of defects in the grain than steaming.

    Yes, I have done steam bending with some nice quality (and very costly) "steam bending" wood from a specialty supplier. It works very nicely and will make more complex shapes. But I can use any old cheap (or free) fairly clear lumber if I boil it, at a fraction of the cost.
     
  6. peter radclyffe
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    peter radclyffe Senior Member

    Steve W, please excuse me, i do not mean hot water and cloth, you are most experienced with steaming, as you know the big problem is to keep the plank too hot to touch and so wet it does,nt crack, i used to steam planks until i went to italy and saw how they put the plank in a steel bath, open at the top with a fire underneath it, it appears to be cheaper to heat than a steamer
     
  7. PAR
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    PAR Yacht Designer/Builder

    Again, it's the heat that does the trick, though adding a lot of moisture can help make it more ductile. If I use heat, sometimes I'll soak the stock for a few days in a tank or simply a trench, lined with a plastic and filled with water. I'll pull this well soaked stock and use a heat gun or a hand held steamer (tile floor cleaner). This usually works well. If I have severe bends, usually in a jig, I use a metal strap on the outside of the bend to prevent blow outs. It's not hard, if the stock is well selected for suitability for bending.
     
  8. rwatson
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    rwatson Senior Member

    6 oz fibreglass and epoxy on the outside of the bend, on any strip of wood, increases the ability to curve without breaking enormously.

    Here are photos of a 5mm strip of Western Red Cedar, glassed on one side, being bent into position without any steaming.
     

    Attached Files:

  9. sprit
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    sprit Junior Member

    Thanks rwatson.
    This is the first new idea I have heard.
     
  10. PAR
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    PAR Yacht Designer/Builder

    On really thin pieces this is true. I bend veneers this way, but on thicker pieces, not much advantage.
     
  11. upchurchmr
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    upchurchmr Senior Member

    Watson,

    Great tip, if it is required.
    Did you actually try putting the 5mm board in the boat without the glass? It might be completely obvious if I tried something similar:)

    I have wanted to reverse this for a SOF kayak. Glass on the inside of the stringers (inside of the curve) to reduce the size of the stringer.

    PAR, I assume veneer means the typical commercial bought really thin stuff?
    I have just finished making a laminated handle for the bow of a boat with 1mm (.040" or a little less) table saw cut "veneers" and had to remake them 4 times due to cracking because of the severe curvature. This was after wetting them and trying to position them on the bending form to pre-curve them before laminating.
     
  12. SamSam
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    SamSam Senior Member

    This is a standard way for bending the sides of guitars.

    [​IMG]

    You mount a capped piped (so you don't scorch your nads) in a vice and stick a propane torch in the open end. Bigger pipes work better for me, but the pipe is what you bend the wood over, so it depends on the curvature of the bend you're making. The small pipe in the picture is needed for the small bend next to the hand, but it also works for the bigger bend.

    Guitar side wood is 1/8" or more thick and 4-6" wide, usually hardwood. Heat is what makes wood pliable, not so much the moisture. You keep steady pressure on the wood while rocking or sliding it over the hot pipe. You just do a short area at a time, but keep the heated area moving along the length as the bend is made. It reaches a temperature and then you can feel the wood become elastic and flexible and then can take a bend and stay bent. It doesn't hurt to spray or wipe water on the wood to keep it from scorching, but the less water the better as then the wood doesn't have to dry before gluing.

    It would take maybe 10-15 minutes or so too bend the sides for a guitar with this crude set-up. If you google 'bending guitar sides' there are a lot of different bending irons shown. It is free form bending, but if there is a pattern or lines to gauge by, areas that aren't correct can be gone back to and 'touched up'.
     
  13. NoEyeDeer
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    NoEyeDeer Senior Member

    That wouldn't be an effective use of glass. As a rough analogy, it'd be like putting glass on one side of foam to make it stronger, instead of building a proper sandwich layup.

    You only want longitudinal strength and stiffness. If you really want to try it, the best way would be unidirectional glass each side of the timber. Or carbon (even better). It'd probably make sense to do the layup before ripping the stringers too.
     
  14. upchurchmr
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    upchurchmr Senior Member

    Noeyedeer,

    Actually I don't want longitudinal stiffness at all, there is plenty.
    All of the stringers and gunwales are in bending, since there is no effective sheer path connecting the longitudinal members.

    What I want is bending stiffness for impact and to regain the bending stiffness I would loose if I down size the stringers.

    I don't understand your analogy with foam. Glass on foam is done all the time, just not a single layer but that is not what I suggested at all. I understand sandwich thank you.
     

  15. rwatson
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    rwatson Senior Member

    The wood had no chance of making the bend unaided. The WRC didn't have that much elasticity.

    I also used the method when I was building a curve in a skate ramp, out of average quality exterior ply.

    The outside of the bend started to splinter when pressured, so I applied 6 oz fg + epoxy on the outside of the bend, and it curved with no further trouble.
     
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