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  1. #1
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    Web Stitch Strength Info

    Here's a neat reference I came across when looking to sew my tree huggers. Looks like the recommended "box with an x" is the absolute worst way to sew webbing! The % number is relative to the webbing itself.
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    New Member Sprite's Avatar
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    That's really interesting. I like that I could do the highest strength option, since my machine doesn't zig-zag for bar tacks. Where did you find this information?

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    Senior Member rjcress's Avatar
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    I think that the strength of different stitch patterns is likely relative to the magnitude, direction, and duration of onset of the force that is applied.
    I would love to read what types of loads and test methods were used to determine the values in this chart.
    Do you have the source?
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    Quote Originally Posted by rjcress View Post
    I think that the strength of different stitch patterns is likely relative to the magnitude, direction, and duration of onset of the force that is applied.
    I would love to read what types of loads and test methods were used to determine the values in this chart.
    Do you have the source?
    Yes, this is from "On Rope", the definitive guide to climbing rope and gear, page 240. The stitch strength shown is relative to webbing sewn longitudinally overlapping, as when forming a loop, or splicing web straps. From this, I inferred that the forces would also come from along the length of the webbing.
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    Quote Originally Posted by Sprite View Post
    That's really interesting. I like that I could do the highest strength option, since my machine doesn't zig-zag for bar tacks. Where did you find this information?
    Yeah, it was also reassuring for me too, since the strongest stitch is the easiest for me. The bar tack fools people. Manufacturers don't use it because it's strong, they use it because they can train unskilled workers to sew it on a bar tack machine with great consistency. Even an old Singer 66 thread shooter can make the strongest straps!
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    Senior Member nacra533's Avatar
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    Good info, but.....

    IIRC, the info is for dynamic (shock) loading of nylon climbing slings and lines. Nylon stretches more than poly, so it makes sense that longitudinal stitches and zig zag will stretch with the line and put less shearing forces on the eye. My data came from Nylon Highway, a climbing resource.

    I do agree in principal with the chart, but the box x is plenty strong for our use and you are more likely to experience strap failure than stitch failure.

    Take a look at nylon and poly lifting slings used in industrial applications. Many have a box x or multiple box x.

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    Report and some testing info ang data

    Read from Page 12 to 16 There is detailed information on thread, stitching and testing
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    Quote Originally Posted by Busky2 View Post
    Read from Page 12 to 16 There is detailed information on thread, stitching and testing
    Cool, that corroborates the info from On Rope that 12 passes in a zig zag, with the length of each pass 2x the width of the webbing itself will be stronger than the webbing itself. It's also easier for me, and doesn't have to be straight to look neat!
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    in it for the naps oldgringo's Avatar
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    I like this for all the right reasons, and one wrong one: it's compatible with my sewing skillz, which are on the shabby side of sloppy. :ashamed:
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    Quote Originally Posted by nacra533 View Post
    Good info, but.....

    IIRC, the info is for dynamic (shock) loading of nylon climbing slings and lines. Nylon stretches more than poly, so it makes sense that longitudinal stitches and zig zag will stretch with the line and put less shearing forces on the eye. My data came from Nylon Highway, a climbing resource.

    I do agree in principal with the chart, but the box x is plenty strong for our use and you are more likely to experience strap failure than stitch failure.

    Take a look at nylon and poly lifting slings used in industrial applications. Many have a box x or multiple box x.
    What I saw when I looked at this was the box x or multiple box x was what was used also. It would not surprise me if the optimum pattern was a function of the webbing material, the structure of the webbing, the tread material, and the size/strength of the treads. Actually, I would expect that.

    Think for a minute about the polyester mule tape, or pull tape. It is light weight because there is not much in the way of threads used perpendicular to the webbing. I would not trust sewing loops in this in general but particularly if they were only sewn along the length of the webbing because there is not much there to hold the stitch.

    In the simplest terms, what you have is webbing with a certain strength and thread with a certain strength. If the webbing is 1500 lbs and the thread is 3 lbs, then you need 500 stitches to match the strength. If the thread is 10 lbs, then you only need 150 stitches to do that. The trick is to get those stitches 'load bearing' while not damaging the integrity of the webbing.
    Last edited by Youngblood; 03-17-2011 at 09:27.
    Youngblood AT2000

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