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Stainless fasteners, going into Stainless material.

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  • #46
    Originally posted by ezduzit View Post
    On yachts, the propellers are held onto the tapered shaft using nut and locknut. Always the (thinner) locknut goes on first.
    I wish I could agree with your "always"! Perhaps you live in an enchanted land.

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    • #47
      You can also get silver plated stainless, it stops galling even under high temps.

      I wish I had only had issues with stainless on stainless. It's almost guaranteed if I am removing a panel with a bunch of stainless screws at least one will gall and snap off.

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      • #48
        There are as many semi plausible arguments for putting the lock nut on first as there semi plausible arguments for putting it on last.

        What I have never seen addressed is how you apply full torque to a thin lock nut applied first without stripping or severely deforming the threads. If the full torque is not applied to the lock nut, how do you calculate the torque required for that nut and the torque required for the following nut so that you end up with the desired clamping load and an effectively locked fastener, taking into account the variable and more often than not indeterminate friction factors?

        Why not simply accept the fact that a nut and a lock nut work extremely well on toy wagons, garden carts, and even on somewhat more demanding applications. But, really, they shouldn't be used for any application where it would make a damn bit of difference which nut was put on first.

        If you insist on using a lock nut, just use two full size nuts, then nobody can tell whether you put the lock nut on first or last.
        Last edited by cameron; 03-23-2018, 08:23 AM.

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        • #49
          Originally posted by cameron View Post
          There are as many semi plausible arguments for putting the lock nut on first as there semi plausible arguments for putting it on last.

          What I have never seen addressed is how you apply full torque to a thin lock nut applied first without stripping or severely deforming the threads. If the full torque is not applied to the lock nut, how do you calculate the torque required for that nut and the torque required for the following nut so that you end up with the desired clamping load and an effectively locked fastener, taking into account the variable and more often than not indeterminate friction factors?

          .....
          I would not expect that you can..... Which is probably why you do not see that done much for really significant uses. On top, or on the bottom. ANY time you tighten one against the other, you are adding load to the top one, and removing load from the bottom nut.

          Makes sense to remove load from the lock nut, which adds load to the actual nut. But that added variable probably fouls up all torque measurements, you'd need to go by a stretch measurement. Even "turn of the nut" nay not do what is expected.

          Both of those assume that the load is being added to the nut against the part surface, but with a locknut that is not 100% true. Some is being taken up with the forces between the two nuts, and figuring out what the distribution of force is would be difficult.

          Mostly it seems they have been used where "snug tight" is good, and you cannot have it actually come off. NOT places where you need a specific clamp force. I don't know how you would really GET that, maybe by a "double turn of the nut" based method.
          CNC machines only go through the motions

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          • #50
            Originally posted by J Tiers View Post
            I would not expect that you can..... Which is probably why you do not see that done much for really significant uses. On top, or on the bottom. ANY time you tighten one against the other, you are adding load to the top one, and removing load from the bottom nut.

            Makes sense to remove load from the lock nut, which adds load to the actual nut. But that added variable probably fouls up all torque measurements, you'd need to go by a stretch measurement. Even "turn of the nut" nay not do what is expected.

            Both of those assume that the load is being added to the nut against the part surface, but with a locknut that is not 100% true. Some is being taken up with the forces between the two nuts, and figuring out what the distribution of force is would be difficult.

            Mostly it seems they have been used where "snug tight" is good, and you cannot have it actually come off. NOT places where you need a specific clamp force. I don't know how you would really GET that, maybe by a "double turn of the nut" based method.
            That WAS a rhetorical question, JT.

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            • #51
              Originally posted by ezduzit View Post
              On yachts, the propellers are held onto the tapered shaft using nut and locknut. Always the (thinner) locknut goes on first.
              Why is it always done that way? Is there a large enough body of recorded, reliable evidence to demonstrate that propellers with the lock nut put on last fall off more often than propellers with the lock nut put on first?

              Or is it just the way they do it down your way?

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              • #52
                Originally posted by cameron View Post
                That WAS a rhetorical question, JT.
                No harm in a reasoned answer..... Call it a rhetorical answer and all is well....
                CNC machines only go through the motions

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                • #53
                  Originally posted by cameron View Post
                  Why is it always done that way? Is there a large enough body of recorded, reliable evidence to demonstrate that propellers with the lock nut put on last fall off more often than propellers with the lock nut put on first?

                  Or is it just the way they do it down your way?
                  When I lived in Seattle my dad worked as a marine propulsion systems technician and he always drilled into me that this is how and why it should be done that way.
                  It is pretty well an industry standard.

                  https://www.passagemaker.com/channel...t-myth-busting

                  Rest assured, not only is this approach one I wholeheartedly endorse, but it’s also backed up with good engineering and it’s endorsed by propeller manufacturers, the Society of Automotive Engineers, the American Boat and Yacht Council, the U.S. Coast Guard, and the U.S. Navy. The latter spells this procedure out in excruciating detail in chapter 75 of their sublime (if you like this stuff) NavShipsTechManual (Chapter 075-5.3.4, Fasteners). It can be downloaded as a pdf, courtesy of Uncle Sam
                  Home, down in the valley behind the Red Angus
                  Bad Decisions Make Good Stories​

                  Location: British Columbia

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