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Which is a stronger mechanical connection

  1. Aug 27, 2017 #1
    im attatching a bolt to the inside of a pvc endcap

    i plan on having a metal plate on the outside so the connection is distributed over an area larger than the nut
    my question is, reguarding strenght of connection, and integrity of endcap
    is it better to go with a single hole (eye bolt) or 2 (u-bolt/cable clamp)

    my worry is that an eye-bolt means all the preasure is centered in one spot
    but a u-bolt means putting 2 holes in rather close proximity, meaning a potential weakspot
  2. jcsd
  3. Aug 27, 2017 #2


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    Why not put large washers ,sometimes called repair washers, both sides of the plastic or plate on one side and large washer on the other.
  4. Aug 27, 2017 #3


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    Also sometimes called fender washers.
  5. Aug 27, 2017 #4
    yeah, after i posted this i thought about just using a washer rather than making plates,
    and using a rubber washer to maybe lessen the chance of cracking

    but my main concern is wether i should use an eye bolt or a u-bolt
    or will it not really matter?
    (so long as i dont crush the heck out of the pvc by tightening it too much)
  6. Aug 28, 2017 #5


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    The above discussions assume a flat end cap. However, some end caps are convex, or domed. Any flat reinforcing plate or washer on a domed end cap will concentrate stress; either around the hole in, or around the periphery of, the end cap.

    You don't say which direction the force is in relation to the pipe. i.e. pulling the cap off the pipe or pushing it onto the pipe. With a domed end cap, pushing onto the pipe, then a plug with a shoulder on it inserted into the pipe would be best. If a cap is still needed, shape the plug to the cap interior.

    If pulling the cap off the pipe, then an insert in the cap, shaped to the cap interior is needed.

    In either case, I vote eye bolt. That leaves more of the weak plastic available for structural strength. (It's also less machining.:smile:)
  7. Aug 28, 2017 #6
    yeah, cap is convex, force pulling in

    you lose me when you say "plug with a shoulder"

    ...but anyways, i had the same thought reguarding eye-bolts (after having bought the other parts)
    just really wanted a second opinion before i made any irreversible moves

    using washers, im thinking i should peen them to fit the concave better (wide fender washer, both sides +rubber spacers)

    thanx much
  8. Aug 28, 2017 #7


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    Here is what I had in mind.
    If the end cap is not needed for sealing, make the top of the plug flat and use a flat washer.
    If the end cap is needed, then your idea of rubber washers inside and outside the endcap would be a definite improvement.

    BTW, how much force are you talking about and what size pipe? I'm also curious about the end use, if it isn't proprietary..
  9. Aug 29, 2017 #8

    jim hardy

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    If it's strength you're after
    see if your local plumbing supply house can get you some schedule 120 PVC .


    I recently did a plumbing job and used some schedule 80 - it's tough stuff.
    Most places just carry household schedule 40.

    old jim
  10. Aug 29, 2017 #9

    jim hardy

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    Don't rule out epoxy . JB-weld from Walmart has strength up to 3900 psi. Underneath @Tom.G 's washer it'd beef up the whole assembly. Get a fender washer big enough to cover the whole cap so it'll be in compression not shear.
  11. Sep 1, 2017 #10
    thanx for the help, and information

    use isnt "proprietary", but nothing dangerous, just wanted a secure end for putting tension between caps
  12. Feb 14, 2018 #11
    and how much tension between the caps (plural?)

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