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Grade 5 Or Grade 8 For Winch?

Discussion in 'Winches' started by radshooter, Nov 14, 2018.

  1. Nov 14, 2018
    radshooter

    radshooter Member

    Tuba City, AZ
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    If I get enough other projects done this weekend I would like to start mounting my winch. The instructions for the mounting plate state use grade 5 bolts (not supplied). Since I have to go buy bolts anyway, would it be a good idea to upgrade to grade 8 instead?

    Thanks,
    Steve
     
  2. Nov 14, 2018
    sterlclan

    sterlclan Member Sponsor

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    Grade 8 bolts have less “give” than a five the five will bend or stretch where the eight may snap. If the manufacturer rated it with fives that’s what I’d use.
     
  3. Nov 14, 2018
    PeteL

    PeteL Member Sponsor

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    x2. I've heard the higher grades are more brittle, if used any place there is a chance of motion.
     
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  4. Nov 14, 2018
    FinoCJ

    FinoCJ 1970 CJ5 Staff Member Sponsor

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    I feel like we had a post (maybe from McRuff) about the grade 8 bolts and how they are NOT brittle - see if I can find....
     
    Last edited: Nov 14, 2018
  5. Nov 14, 2018
    Mcruff

    Mcruff Earlycj5 Machinist Sponsor

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    I'll just leave this here, this is a very old argument. But in my opinion if your life may depend on it don't trust the lesser quality.

    You can see the yield(stretch or bend) strength is over 1200lbs higher on a grade 8 over a grade 5, and the failure strength is nearly the same, brittleness has nothing to do with it so long as the bolts are properly torqued. And fine threads are better than course thread if you can get them.


    Grade 8 bolt capability in yield (stretch) = 130,000 lbs / in2 x .03349 in2 = 4354 lbs minimum
    Grade 8
    bolt capability in tension (failure) = 150,000 lbs / in2 x .03349 in2 = 5024 lbs minimum
    Grade 5
    bolt capability in yield (stretch) = 92,000 lbs / in2 x .03349 in2 = 3081 lbs minimum
    Grade 5
    bolt capability in tension (failure) = 120,000 lbs / in2 x .03349 in2 = 4019 lbs minimum
     
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  6. Nov 14, 2018
    sterlclan

    sterlclan Member Sponsor

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    ill bow to the man that would know...
     
  7. Nov 14, 2018
    FinoCJ

    FinoCJ 1970 CJ5 Staff Member Sponsor

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    I am copying this from Mcruffs post in another thread, but seems to be worth applying here as well...the tech report link should still be active...

    A grade 5 will have reached its yield strength surpassd that and sheared off before a grade 8 bolt begans to deform or yield. A grade 5 bolt is not superior to a grade 8 in any condition at all period!!!!!!!!!!!!!!!!

    The shear of a grade 5 bolt in 7/16" is 11,270# , the same size grade 8 is 13,680# the tension on the same grade 5 bolt is 13,338# the grade 8 is 16,673#, so you can see the grade 5 would have already failed befoer the grade 8 started to deform.

    To all in doubt read this article; Fasteners: Making the Grade - A Technical Discussion - RockCrawler.com or break out a machinist handbook.
     
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  8. Nov 14, 2018
    Chilly

    Chilly Active Member

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    % elongation is a mechanical property characterizing how much fastener will yield before fracture. Silly Putty has a very favorable % elongation but a very poor yield strength (force required to cause permanent stretch).

    Agree that the only circumstance where a Gr5 beats a Gr8 is where a Gr5 is more than sufficient, and I'm the guy writing the checks to buy lots of them.
     
  9. Nov 14, 2018
    PeteL

    PeteL Member Sponsor

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    Question...

    So then why do we need to even have a Grade 5 if there is Grade 8? The cost difference in material or manufacture can hardly be significant. (Cost, not price!)

    McGruff refers to "properly torqued" fasteners. But the rumor I've heard is that the higher grade may work-harden, or suffer fatigue failure, in an application where there may be movement.

    Another interesting thought is this nugget. Wood fasteners (pegs, or 'trenails') in coverered bridge trusses actually outperform metal fasteners (bolts). The reason is that in a tight metal to metal fit, when one bolt fails the extra load is thrown entirely onto the next, over-stressing it. Each accumulated failure results in a "zipper" effect. The tables above only consider a single fastener.

    By contrast, as wood pegs are overloaded, they deform such that the load is gradually transferred and shared among fasteners, postponing failure. Each peg in the sequence assists the next, rather than pushing it to suddenly shear. I have been told that wooden bridges may outperform engineering calculations by a factor of ten.

    Deformation can be a good thing!

    (And, remember the engineer who calculated that bumblebees can't possibly fly.)
     
    Last edited: Nov 14, 2018
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  10. Nov 14, 2018
    Mcruff

    Mcruff Earlycj5 Machinist Sponsor

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    Because you as a consumer don’t count, but when GM, Ford or whomever buys bolts they buy them by the train car full, at a .05 per fasteners savings it amounts to 100’s of thousands of dollars a month. The right fastener for the right load at the right cost for the job.

    You are quoting a lot of heresay and misinformation about bolts and wooden pegs.
    When a bolt fails the load is distributed just like your wooden peg explanation.

    So you think that a grade 8 bolt can’t bend. You are very ill informed if you believe that, I posted a picture of several grade 8 bolts 1” in diameter 8” long that were bent more than 40° and did not crack or shear.

    Work hardening is a by product of movement not load, if the bolt does not move around or is not cycled through heat it won’t work harden.
     
    Last edited: Nov 14, 2018
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  11. Nov 14, 2018
    PeteL

    PeteL Member Sponsor

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    I don't think I said that exactly.
    But I did say 'fatigue' and 'work harden' which actually are forms of bending.
     
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  12. Nov 14, 2018
    Mcruff

    Mcruff Earlycj5 Machinist Sponsor

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    If all things are equal why would a grade 8 work harden faster than a grade 5 bolt.
    Remember work hardening is a product of the right material, stainless steel, copper, brass and some aluminum hardening due to rubbing or heat cycling. Most steels do not work harden.


    The bumblebee thing is a myth!
     
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  13. Nov 14, 2018
    PeteL

    PeteL Member Sponsor

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    Well, by definition, they are not equal. Stands to reason they'd behave differently, or they would not have different classifications and applications.

    I'm only guessing, but presumably they are different alloys, or heat treated differently, or both.

    Just putting it out there for discussion, I am not trying to prove anything.
     
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  14. Nov 14, 2018
    PeteL

    PeteL Member Sponsor

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    That surprises me to hear.
    What is it when you bend a paperclip until it breaks, or a piece of fence wire? Or the front fender or a frame member on a Jeep develops cracks?
     
  15. Nov 14, 2018
    Mcruff

    Mcruff Earlycj5 Machinist Sponsor

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    It’s called structural fatigue from bending. Springs are hardened and tempered to be a certain hardness. Bolts will do the same thing if bent back and forth, so will wood, plastic and everything else.

    Aluminum is one of the worst it is one of only a handful of metals that have a cyclic life.
     
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  16. Nov 14, 2018
    Chilly

    Chilly Active Member

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    Steels have a cyclic stress level below which the material can survive indefinitely. So a properly torqued fastener of a correct design will theoretically never fail from fatigue.

    Other metals such as aluminum HAS NO SUCH THRESHOLD. A bumblebee flapping its wings near an aluminum rod will eventually cause it to fail. Except that bumblebee flight is a myth.
     
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  17. Nov 14, 2018
    Chilly

    Chilly Active Member

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    I guess I'll have to disagree that most steels dont work harden. Alloy steels such as rifle barrels may benefit from cold-forging over a mandrel that is the shape of the bore, including the rifling. A cold hammer forged barrel is as tough as they come due to the cold working of the steel. The steel is hardened during the cold plastic deformation. This is not applicable to a bolt, though. It will not work harden until it plastically deforms, but at that point the joint is already failed.

    So a steel bolt will work harden, as it is being torn away from the Jeep. If a bolt doesnt yield it does not work harden, and does not become more brittle. Work hardening steel requires plastic deformation: ie, yield failure.
     
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  18. Nov 14, 2018
    PeteL

    PeteL Member Sponsor

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    Such as bending a paperclip or a fence wire...? :whistle:
     
  19. Nov 14, 2018
    Chilly

    Chilly Active Member

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    Im reading between Mcgruff's lines that most steels will not work harden inside of plastic def?
     
  20. Nov 14, 2018
    WYOMIKE

    WYOMIKE Oct 1971 pic Sponsor

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    In my humble opinion, and I do not know a lot amount work hardening, etc. but from personal experience I think that you will find that something on the Jeep frame itself will fail long before the winch bolts will fail even if just grade 5. At least with a PTO winch. Don't ask how I know :rolleyes:

    Mike
     
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