Pop Rivet vs Screw..Which is stronger?

Discussion in 'Materials' started by rebar, May 9, 2012.

  1. jehardiman
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    jehardiman Senior Member

    Been there, done that, generally doesn't work that well. On composite and steel the stud patches work well but for aluminium the surface activity of the metal is too high and it oxidizes, leaving the epoxy attached to weak aluminium oxide which just pulls off. Physically roughening the surface(80-100 grit) followed by a acid wash is necessary to get enough tooth for the epoxy to stick well and even then the usual result is the patch tears away before the bolt breaks becuase of the reduced tensile adhesion area.

    Edit; besides, he's looking for a innie, not an outie.
     
  2. Herman
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    Herman Senior Member

    Use MMA glue, not epoxy.
     
  3. PAR
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    PAR Yacht Designer/Builder

    Unless the patch is quite large, I agree that bonding a stud to aluminum isn't an ideal solution.

    Sorry Rebar, I missed the aluminum wall portion of your posts. So we have a flat (assumed) .125" thick, T-6 aluminum wall with limited reach behind and no access behind. Right?

    Can you weld to this wall? How important are cosmetic or aesthetic considerations?

    I'm reminded of something I've done previously in similar situations. I've drilled a1/2" hole and inserted a thin wire with a bundle of 'glass fabric attached to the end. I then smash thickened epoxy in the hole, enough to make a significant wad on the inside, when the wire and fabric ball are pulled up tight against the back side of the wall. The thickened goo smashes flat(ish) on the back side, then cures into a mushroom shaped hunk of plastic. If you substitute the thin wire for a stud, you're probably good to go.

    I still think a thick wall stainless insert will work as well, considering the loads involved. How big a hole do you have available for the tie downs, as this will be the determining size for the nut insert? If you can get a 1/4" insert in there, you're way over your required strength.
     
  4. rebar
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    rebar Junior Member

    No reach behind or any access due to aesthetic concerns. The tie downs are countersunk for two 1/4" screws each. These tiedowns have removable rings which leaves a good looking button when not in use.

    Will this work long enough to set say, 50 SS inserts? Or do I need something beefier for SS?
     
  5. PAR
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    PAR Yacht Designer/Builder

    I'm not familiar with that tool or company. You'd be best advised to check their site for technical specs on their rivet nuts. I did notice the tool was carefully photographed to exclude the manufacture's name and also that it wasn't recommended for stainless steel rivets, which is a good indication of it's quality.
     
  6. rebar
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    rebar Junior Member

    Just ordered these.. Might try a home made tool before I order something.
     
  7. Saildude
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    Saildude Junior Member

    If you are only doing a few fasteners one time - you might give your local tool rental places a call - they might have some sort of setter that you could rent for a day or two.
     
  8. P Flados
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    P Flados Senior Member

    You may be able to simply:

    • thread a nut on a bolt
    • stack a few flat washers
    • screw on the expansion nut
    • insert and then tighten the nut with one wrench while holding the bolt with another wrench

    Use a good quality bolt & nut along with a little lubricant and it should pull up. More tedious than the tool, but not a big deal for a handfull.
     
  9. PAR
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    PAR Yacht Designer/Builder

    The hard part with home made or tools of dubious quality, is how much sleeve compression they provide and most importantly, that it stops the compression process at maximum crush range, for the particular rivet selected. You can easily over or under compress the sleeve and ruin it's holding power with a Mickey Mouse tool.
     
  10. rebar
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    rebar Junior Member

    Can you make a suggestion on which tool you would get if you were installing less than 100 of the SS rivnuts I ordered please?
     
  11. PAR
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    PAR Yacht Designer/Builder

    [​IMG]

    PNT 110 pop rivet insert tool. Probably less the $50 at the local tool store. The problem with your needs is most of the cheap pop riveters can't handle a 1/4" stainless rivet. Actually they can, but will break in fairly short order. Personally, if it was me and I didn't have the riveter I do, I'd pick up a reasonable quality medium duty riveter that could do 1/4" inserts, even if it says not for stainless. I'd use it knowing it'll be dead or near so, after a few hundred rivets, but so what, the job would be done. Or you can buy a good riveter and get many years out of it. I have a good one and it has long since paid for it's $150 initial investment. You're call. See if Harbor Freight has one that can work with inserts.
     
  12. rebar
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    rebar Junior Member

    I tried that, but the nutsert kept spinning in my 1/8" test aluminum.

    What did work was a tool similar to the one shown in the video I posted a few posts back. A handle from 1 x 1/8 aluminum bar stock with a offset bent to keep your fingers safe. Instead of the stud and hex coupler in the vid.. I simply slid a grade 8 bolt and washer through a hole in the bar stock handle and cranked. Worked great if the nutsert hole was a tight fit.


    My question now is how much compression is best? I pulled the aluminum threads right out with 1 1/2 turns before I saw any mushrooming so I decided against them even through the nutsert felt tight. The SS compressed well. I could see the mushroom but I continued until I broke the grade 8 bolt which was 4 (.2" pulled) complete turns. I then tested a few others at 3 turns (.15" pulled) and they were definitely mushroomed well, and didn't break the bolt. But the threaded nutsert hole wasn't centered and a bit crooked after the compression which made me wonder if I was compressing to far.

    So is there a rule of thumb on compression? Does the off centered nutsert threads indicate I compressed to far? Or was it the home made tool which did that?:confused:
     
  13. rebar
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    rebar Junior Member

    After waiting for the parts.. I installed a few SS nutsert/rivnuts to secure the ancra tie downs for the tool box. I might install another piece of oak to synch down to.. But Im thinking my tool box wont go anywhere..

    Thanks for the suggestions!
     

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  14. PAR
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    PAR Yacht Designer/Builder


  15. SamSam
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    SamSam Senior Member

    Consider the whole is top heavy, the strap is below the center of the mass, load that up with 400# of shifting weight, add inertia and a sudden stop.
    To tell the truth, it looks to me the answer to my post #18 is 'it's just a guess'.

    Going by "if the weather got really rough and the vessel was capsizing." I envision possible hours of back and forth movement, where each time the ability of the fasteners to hold would be tested, at shock loads that might be at the limit or more. Each time the force would be transferred to the 'weak link' interface between the hard SS rivet thing and the soft ductile aluminum stud. The joint might be strong enough for an X amount of load, but the question is if it's strong enough for that load repeated hundreds of times.

    On the one hand the rivet thing seems to be a reasonable way to solve the problem, but if it was me I would put another set of tie downs up towards the top. I think (all this is 'just an intuitive guess') it might be one of those exponential things, like doubling the tie downs might make the system 3 or 4 times stronger. With two straps, I think then you could transfer your worries to whether or not the wall will stay straight under the load, and not whether a 3-400# object will be rolling around loose.

    Northeast Iowa is some serious rural, I like it. What sort of boat do you have? Are you on the Mississippi? I am seriously thinking that living on a house boat on the upper Mississippi is where I need to be. The good thing is, my wife agrees! What's even better is she would like to be with me, too!
     
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