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  1. #11
    GrizzlyAdams's Avatar
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    Quote Originally Posted by JerryW View Post
    My first reaction is *be very careful*! The diameter and wall thickness of arrows would likely be too small to handle the enormous compression forces of a bridge hammock. Any slight flex and it would bend and break, possibly sending shards of carbon tube in every direction.

    A larger diameter, thicker wall carbon tube(tent pole?, kite strut?) might work, but I don't know of a way to calculate the proper size. The trial and error method could get very expensive.

    We know that an aluminum hiking pole will work, as well as an aluminum tent pole, but how does that relate to carbon fiber?

    Grizz? You out there?


    Jerry
    Grizz phoning home.

    I doubt very much an arrows shaft is going to do it. Compression strength increases with diameter significantly (something like diameter^2 or diameter^3, Rapt will know), something on the order of a hollow carbon hiking pole like gnome's or fatter is the way to go I think.

    BER is taking one for the team, he ordered some hollow carbon poles over 0.5" in diameter. If we hear back in a couple of weeks or so we'll have data. If we never hear from him again, well then I guess it didn't work
    Grizz
    (alias ProfessorHammock on youtube)

  2. #12
    Senior Member CatSplat's Avatar
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    A quick back-of-the-envelope calculation tells me that in general, for a bridge hammock, the compressive force in those members would be around half the hanger's weight, depending on load distribution and fabric angle.

    Even my stiffer 7595 arrow shafts would likely (eventually) shatter under that kind of sustained compressive load. A cool idea indeed, but I would shy away from using the arrows.

  3. #13
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    Quote Originally Posted by GrizzlyAdams View Post

    BER is taking one for the team, he ordered some hollow carbon poles over 0.5" in diameter. If we hear back in a couple of weeks or so we'll have data. If we never hear from him again, well then I guess it didn't work
    Yes, as Grizz mentioned, I placed an order 2 days ago from Rockwest Composites for a couple 72" CF tubing with inner diameter of 0.5" and outer diameter of 0.56 with a wall thickness of 0.03" (item# 45166). I have received shipping info so should have them in a couple days. If my calculations are correct it should decrease the weight of my spreaders from ~9.9oz to 3-4oz.

    Rockwest has a lot of different tubes available. I chose the one I did because 1) they were fairly close to the size specs of 0.625" aluminum tubes from Quest that I use now and 2) at 72" length, I can cut the tube to get the desired length spreaders with minimal waste. It should be noted that these will not be collapsible, but have noted that the 0.625" aluminum poles fit into the backpad of my pack and could be used to replace the aluminum stays (albeit uncurved like stays). This might be one way to carry the longer CF tubes. It remains to be seen.

    Shipping costs were rather high (almost as much as the tube itself), but I suppose that is to be expected with an oversized item.

    I will make a separate thread to report once they arrive and have had a chance to test them with the next iteration of my DIY bridge hammock.
    Last edited by BER; 10-12-2011 at 18:38.

  4. #14

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    What about bamboo as spreader bars?

  5. #15
    Fish<><'s Avatar
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    As with any other man made fiber, if you decide to cut one up to try it, wear a respirator or atleast a face mask. You dont want to have those little splinters floating around in your lungs...just a thought on safety for what its worth.

  6. #16
    New Member
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    Quote Originally Posted by Catavarie View Post
    Or you could go with carbon fiber golf club shafts, longer length and thicker walled, still uncertain if it would be strong enough to avoid flexxing, as that would cause the snap of the pole.
    Graphite golf club shafts come in various flex ratings. extra stiff would be the best option although still too whippy for a bridge. They do not break clean either If someone is brave enough to try , the best deals are at large full-service golf pro-shop where they service clubs, change grips, shafts etc. There are bound to be some used shafts laying around for cheap. New ones are insanely expensive.

    Has anyone tried using old rattan canes? They seem to have a good, weight/strength/flex ratio.

  7. #17
    New Member johnnyh88's Avatar
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    One arrow shaft might not work, but 2 or 3 bound together maybe? Not sure what the point would be then.

    rcfoam.com has a wide selection of carbon fiber tubes (all a meter long though and I'm not sure how wide they need to be a for bridge): http://www.rcfoam.com/index.php?cPat...5075a4978e5dd3

    Something like an elliptical or flanged tube would be best for the weight (http://www.rcfoam.com/product_info.p...5075a4978e5dd3). That would get you a lot of material where on top where the compression force in the spreader bar is the highest and less material on the bottom where it doesn't matter as much.

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