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Cotter pin versus screw pin on turnbuckle jaw

Discussion in 'Scenery, Props, and Rigging' started by BillConnerFASTC, May 13, 2019.

  1. BillConnerFASTC

    BillConnerFASTC Well-Known Member

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    I'm preparing bid docs for some repairs based on a report by a rigging contractor and one of the items is citing a turnbuckle in the load path with cotter pins used to retain the clevis pin as not appropriate for stage rigging. Its forged, its sized and rated appropriately, where is the problem? And if it is a problem, why does this product exist.

    Thanks.
     
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  2. Amiers

    Amiers Renting to Corporate One Fixture at a Time.

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    I’m confused. Are the turnbuckles U or 0. Maybe they specced the wrong item and the pin comes with that item.

    I would assume a U turnbuckle is used for sailing where in case there is to much of a load the cotter pin goes and saves the boat from having a hole in it.


    Edit:
    So after thinking further. It could be a cost or addition to a preexisting point.

    You can’t drop an eye onto an eye without an extra piece of hardware. So you are stuck with pin and clevis or hook ( hook sucks ). Personally if you go the U /jaw route see if you can get a rated bolt and locknut instead of cotter pin. You will sleep better at night but will cost more.
     
    Last edited: May 13, 2019
  3. Colin

    Colin Well-Known Member

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    User error causes line to go slack, jaw gets side/diagonally loaded just right for cotter pin to fail, no? Thus there exist jaws with bolt and nut plus cotter to retain the nut. Also I've found missing cotter pins, whether never installed or came loose.
     
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  4. bobgaggle

    bobgaggle Well-Known Member

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    Maybe because cotter pins are a real pain to work with. If its a rig that may get disassembled somewhat regularly, standard cotter pins would break from fatigue. Hairpin cotters would do better...
     
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  5. Van

    Van CBMod CB Mods Premium Member

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    It's definitely NOT industry standard.
    I cannot imagine a case in which a cotter pin would be subjected to enough stress to actually have to worry about its shear strength for retaining the clevis. However, if someone is using 'non-industry-standard' turnbuckles it would lead me to wonder what else on the rig is non-standard. If I saw it during a rigging inspection I would certainly list it as a potential hazard.
     
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  6. BillConnerFASTC

    BillConnerFASTC Well-Known Member

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    It's a 1990s install by a very respected major company, thought electrics could have been replaced by an EC. Don't know. I don't see an issue where the cotter pin is stressed or anything that makes it unsafe. upload_2019-5-13_14-31-17.png
     
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  7. Van

    Van CBMod CB Mods Premium Member

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    Wow, that's a teeny tiny cotter pin. Again, I can't imagine a situation where you'd have to rely on it to retain the clevis pin but Damn! it looks undersized.
     
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  8. egilson1

    egilson1 Well-Known Member Premium Member

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    It has to do with that when you get near YEILD of the turnbuckle the forked end tends to "open" or widen and you can suck the cotter pin through the hole in the forked end and hence the pin becomes dislodged. I have seen this in my own distructive testing, but I am not sure I agree with the blanket theory of you can't use them for stage rigging. Some manufacturers say yes, some say no. clear as mud.

    Ethan
     
  9. BillConnerFASTC

    BillConnerFASTC Well-Known Member

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    You know the easy no-liability way out when you are hired to do plans and specs for safety repairs to rigging as a result of a study - just replace the system. I am saying replace the turnbuckles simply because if they hire the same inspector in two years, it just shows up again. I'd rather have them find something different. :)

    I am going to explain my disagreement in a review meeting, so they can take the responsibility.
     
  10. BillConnerFASTC

    BillConnerFASTC Well-Known Member

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    So each of 7 on the set have a yield probably twice or more the entire set capacity, so somehow someone manages to hang it up and put the entire load on one line - and it still half the yield. And the cotter pin is the concern?

    Interesting faq on shackles. I wonder how much of the clevis aspects readily applies to jaw turnbuckles. https://www.lawsonproducts.com/pdfs/PIRMH_Shackles_Clevises_PI.pdf

    This caught my attention: "NOTE: Alloy steel shackles should be used for overhead lifting. Shackles with round pin solely restrained with a cotter pin are not recommended for overhead lifting." As an advocate for alloy chain for overhead lifting, I guess I'll have to become an advocate for alloy shackles. (This sure blows one of the defenses of non-alloy chain - that it is not overhead lifting when it doesn't pass over a sheave.)
     
  11. AlexDonkle

    AlexDonkle Active Member

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  12. Van

    Van CBMod CB Mods Premium Member

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    Just another heads up; The mousing wire/safety wire is wound in the wrong direction. I'd double check everything in the 'new' work.
     
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  13. Colin

    Colin Well-Known Member

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    Ethan's explanation makes most sense to me, but to further illustrate how fuzzy the topic is, I'm looking at a 2013 inspection report from Bill Sapsis who cited the round pin shackles on our trim chains saying:

    "The use of cotter pin shackles is not appropriate for this application. Should a side load condition occur the cotter pin may not be able to support the weight."

    Still it's hard to imagine how the cotter pin could get loaded so much even with the shackle side loaded unless as Ethan says the rest of the hardware yields first.
     
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  14. DavidJones

    DavidJones Active Member

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    I think this is a case where It might be completely fine, but because in SOME applications, they would not be advisable to use. it's way easier just to make a blanket statement that only Screwpin be used. Otherwise, you have people in conversations like this one, and possibly ending coming up with the wrong conclusion. A screwpin shackle will work for all of the mentioned applications, so its easiest just to spec those and not worry about where you can use one and not the other. I could see a contractor mixing things up and accidentally using the wrong hardware in the wrong place if both types are on site during an install.

    This Is kind of the same thing as using Gac-Flex spansets over polyester spansets. Just always use the Gac; it's not worth arguing with every self-proclaimed expert rigger you meet.



    Edit: for spelling/typo.
     
    Last edited: May 16, 2019
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  15. BillConnerFASTC

    BillConnerFASTC Well-Known Member

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    I would agree that starting from scratch, use the screw pin or better pin and nut with cotter pin. But this is repair and maintenance and whether they should be replaced. Is it worth the cost?
     
  16. DavidJones

    DavidJones Active Member

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    That's a good point. At a certain stage, even if it's safe, if someone is going to get stuck on the issue and make things more difficult going forward, I'd rather just spend the money and not have the frustration. But I'm not the one writing the check.
     
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