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  1. #11
    Senior Member WV's Avatar
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    Quote Originally Posted by KenDen View Post
    Very timely post JJ. Thanks for the pics Grizz.

    I finally ordered a panel of CT1K.08 cuben yesterday to do something similar. The real issue that I see with using cuben in a bridge is dealing with peel strength of all of the hems. The best way to stop peel is to sew but then the problem is dealing with the stitch holes opening up. I have seen posts that have shown that Hysol adhesive does pretty well with peel but I have not been able to test it yet.



    A nine meter panel is just about perfect to make a 11x9 Tarp and Bridge Hammock.
    Are you sure that a folded and glued hem will have any peel forces exerted on it? Even shear forces may be minimal, but Griz can address that better than I can. For my cuben tarp I don't plan to hem the edges at all (at first) because I'm not sure how necessary they are.
    I suspect you made the perfect choice of cuben for this. It's gonna be awesome.

  2. #12
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    Are you sure that a folded and glued hem will have any peel forces exerted on it?
    I dont know for sure but it seems to me that while laying in the hammock all of the force from my body is applying a peel force on the folded edges of the arc that will try to unfold it. Would that not be a peel force? I think that is different than the forces of a lap seam across a ridge line.

  3. #13
    Senior Member WV's Avatar
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    Quote Originally Posted by WV View Post
    Are you sure that a folded and glued hem will have any peel forces exerted on it?
    Quote Originally Posted by KenDen View Post
    I dont know for sure but it seems to me that while laying in the hammock all of the force from my body is applying a peel force on the folded edges of the arc that will try to unfold it. Would that not be a peel force? I think that is different than the forces of a lap seam across a ridge line.
    Not sure. It seems to me that the two surfaces are still sliding past each other without separating, even if the cuben is making a 180° turn at the edge. If my tarp raw edge doesn't look like it will hold up, I may try taping and sewing, keeping some alcohol handy to keep it from gumming up the needle. (Bear in mind, when I say "taping" I mean using adhesive transfer tape, which is more like applying glue in an even roll. There isn't any backing or "tape". I find it less messy and much stronger, but I haven't tried sewing through it yet.)

  4. #14
    Senior Member GrizzlyAdams's Avatar
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    Quote Originally Posted by KenDen View Post
    I dont know for sure but it seems to me that while laying in the hammock all of the force from my body is applying a peel force on the folded edges of the arc that will try to unfold it. Would that not be a peel force? I think that is different than the forces of a lap seam across a ridge line.
    I'm not sure what a peel force is, but where the force is strongest near the corners the folded fabric curled, eliminating the folds. Part of the challenge of
    a "no sew" approach is dealing with that. I thought about slipping in popsicle sticks…

    When you sew you get the stretch holes along the suspension edge, but that can be mitigated by taping, to take some of the force off the holes.
    Grizz
    (alias ProfessorHammock on youtube)

  5. #15
    Senior Member WV's Avatar
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    Quote Originally Posted by GrizzlyAdams View Post
    I'm not sure what a peel force is
    Griz, dictionaries say shear force acts parallel to a plane, as in two surfaces sliding past each other. Peel force acts perpendicular to a plane, as pulling one surface away from another. One good example of applying peel force is removing a bandaid.

    Tossing the dictionary aside, you may have meant you weren't sure how peel force would be generated in normal use of a bridge hammock, and I'm not sure either. But then, it's also not that easy to identify the exact source of shear forces. The stretching of the needle holes in a sewn seam suggests that the forces acting on that area are parallel to the sewn surface (hence, shear). Your photos tell me more about what's going on than the dictionary.

    I have sought to clarify some terms we're using, as I understand them, but I don't think I've added much to how they affect hammock construction. Shall we move on to tension and compression?

  6. #16
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    I'm not sure what a peel force is, but where the force is strongest near the corners the folded fabric curled, eliminating the folds.
    I was planning to glue every 1/2 inch fold as I went. I was thinking that this would help stablize the structure. I was also extending the folds beyond the hammock body so that I could attach the suspension&spreader directly to the cuben via a ring or something. Do you think that may help control the forces? I would attach a picture if I knew how.

  7. #17
    Senior Member WV's Avatar
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    Quote Originally Posted by KenDen View Post
    I was planning to glue every 1/2 inch fold as I went. I was thinking that this would help stablize the structure. I was also extending the folds beyond the hammock body so that I could attach the suspension&spreader directly to the cuben via a ring or something. Do you think that may help control the forces? I would attach a picture if I knew how.
    Extending the folds beyond the hammock body sounds like gluing up a strap of cuben, an interesting idea. You may find that you don't need very many folds to get a very strong strap that way, which would be good because too many glued layers could get heavy. Gnome's connector (tape around a carbon graphite tube, creating a toggle) would be excellent in place of a ring.

  8. #18
    Senior Member GrizzlyAdams's Avatar
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    peel force

    got it. Thanks for the explanation.

    I have used the double sided tape that questoutfitter's sells, and the epoxy "Loctite U-10FL" to bond sides of different cuben layers.

    I rolled suspension edges and with the last roll laid down double sided tape. Two things happened. One I've described before, that inside the folds not taped together, the fabric curled up tight, which just seemed like it couldn't be good. Second, even though it seemed to hold, laying in the hammock I could hear what I interpreted as one layer that was bonded by the double-sided tape pulling slowly away from the other. Not a comforting sound! To address that I took 1" side single sided tape (also sold by questoutfitters) and taped the rolled edge to the body, covering the edge that was starting to pull away. That seemed to take care of it.

    I have also used 3M seamstick basting tape. I'm not sure yet of how well that works holding things down.

    But the main thing is that with all the afixing of sides together I've done, I've not seen peel force take apart the fabric. The one exception is this case and there the peel force was preceded by sheer force caused by me sitting on this edge. The dynamics of my butt ripping the hammock side to shreds on our (short) way down to the ground are fun to giggle at but hard to imagine.

    I too had thought about putting a layer of double-sided tape down with every fold, but the questoutfitters tape is relatively heavy for that, and I've been working with more folds (e.g. 6) than are typical for rolling fabric over webbing. I don't know how few folds I can get by with. Every experiment is expensive!


    As long as this work has been outted, perhaps tomorrow I'll be able to pop out the current model and take a couple of pictures.
    Grizz
    (alias ProfessorHammock on youtube)

  9. #19
    Senior Member GrizzlyAdams's Avatar
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    Quote Originally Posted by KenDen View Post
    ... I was also extending the folds beyond the hammock body so that I could attach the suspension&spreader directly to the cuben via a ring or something. Do you think that may help control the forces? I would attach a picture if I knew how.
    Yes, my later versions do this. I epoxied an extension beyond the body that is folded over as part of the roll of the suspension edge, making a strap that, when folded back, creates a loop.

    photos tomorrow for sure, at least of this (which I can do even if it is raining).
    Grizz
    (alias ProfessorHammock on youtube)

  10. #20
    Senior Member GrizzlyAdams's Avatar
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    Quote Originally Posted by WV View Post
    ...Gnome's connector (tape around a carbon graphite tube, creating a toggle) would be excellent in place of a ring.
    I missed that...it's brilliant.
    Grizz
    (alias ProfessorHammock on youtube)

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