Avex countersunk rivets?

Discussion in 'Sheet Metal' started by geosnooker2000, Jul 25, 2019.

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  1. Jul 25, 2019 #1

    geosnooker2000

    geosnooker2000

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    I have noticed Hummel H-5s use 1682-0412 rivets. I am looking for a flush rivet to use on a Zenith CH 640 type project, and don't want the hassle of bucking solid rivets. I have been all over the YouTubes high and low looking for a video dealing with FLUSH blind rivets. Can't find any. Even the 15 part Hummel H-5 assembly video doesn't show any riveting being done, it only shows parts assemblies and clecoing. Then it cuts away and comes back with the riveting already done. I have seen this guy show his flush-riveted work, but he never discusses how the rivet head is formed or augmented (if at all).



    According to this chart by Avex, they meet or exceed the ultimate shear of the rivets Zenith specs:

    https://www.erivet.com/catalogimages/AVEX.pdf

    Here is a statement on the Aircraft Spruce site on behalf of Zenith:

    The Zenith blind rivets are made from quality alloys, and are batch tested by Zenith Aircraft Company for shear strength before being shipped.

    These rivets are corrosion resistant, and the stem becomes locked in after being set. Also, not many different lengths are required for different diameters or thicknesses. In the Assembly Instructions, they are designated as A4 (1/8) and A5 (5/32).

    They have a design shear strength of 130 lbs. and 220 lbs. respectively. Use only Zenith rivets supplied with the kit.

    Zenith Aircraft Company has developed a unique process for setting blind rivets, which requires custom rivet heads. The process uses flush-type rivets, where the flush rivet head is formed into a domed-head by the riveting process. This provides an permanent tight finish to all set rivets. To accomplish this, the riveter heads must be ground (machined) with a concave dome (see diagram). Only 1/8" (A4) and 5/32" (A5) rivets are required to assemble the kit.

    Zenair blind rivets for the ZENAIR Riveting System
    ZENAIR blind (or pulled) rivets have been used to construct the all-metal Chris Heintz designs since the 1970s, and make riveting a quick and easy process! The ZENAIR riveting system forms the rivet head as the blind rivet is pulled, providing a low profile dome finish and high shear strength. Fast installation, simple tools and low cost make this a popular riveting system with homebuilders!


    Which makes it sound like they use the exact same rivet. My big question is, if there is such a thing as a flush blind rivet, shouldn't one be able to install it in a flush manor? Wouldn't that be the whole point of manufacturing such an animal?
     
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  2. Jul 25, 2019 #2

    Turd Ferguson

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    I have some blind “flush” rivets at home. The work has to be dimpled
    Or countersunk as appropriate.
     
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  3. Jul 25, 2019 #3

    BoKu

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    Yes, flush head pops are just flush head rivets you pop in countersunk or dimpled holes. The one ususal gotcha is that most pops have 120-degree heads, while most driven rivets use 100-degree. In practice it hardly matters, but if you want to be precise you can get 120-degree countersinks and dimple tools.

    In the Vans world, Emhart MK319 monel pop rivets are considered an acceptable substitute for AN426AD3 rivets in many skin applications. Most builders try to minimize their use, and purists go to heroic lengths to avoid them altogether, that being what purists do. But they're great for tight spots and places where you're closing out and can't get to the back side. Beware that even though an MK419 has a 1/8" shank, the MK319 shank is actually 7/64", not 3/32" as you might expect. A #34 or #33 drill is about right.

    BTW, I have a crap ton of Avex 1604 c'sunk pops (I think they're the -0412 length) left over from the Schreder inventory. I'd let them go for a nickel each. I also have a lot of MK319 and MD319, but those go at Wicks rate minus 20%.
     
  4. Jul 25, 2019 #4

    geosnooker2000

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    Okay, so 2 in favor of what I was thinking... now, the Zenith riveter head is custom-concave-domed to accomplish their design method (Domed heads). However, in searching out this question (Flush heads) on this forum before I posted, I came across the guy who was asking about gaps between his rivet heads and the sheet work. People in that thread determined that he didn't have a good clean dome grind, or the head wasn't perfect or something to that effect. Am I correct in assuming that if you are going to use flush head blind rivets, you use a stock riveter head without creating a dome, and you HAVE to dimple the holes, or else you'll end up with the same problem this guy had?
    https://www.homebuiltairplanes.com/forums/threads/gaps-under-pull-rivets.26496/
     
  5. Jul 25, 2019 #5

    BoKu

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    Based on my experience, I believe those statements to be nominally true, except that you don't necessarily have to dimple the holes, you can also countersink them, or use a combination of dimpled holes in one piece and countersunk holes in the other. In any case, in my shop we use standard hardware store and Harbor Freight pop riveting tools to install countersunk pop rivets in dimpled and countersunk holes. Pull test results indicate that they are performing about as specified.

    I think that guy was doing the Zenith trick of doming the flush-head rivets during the pull to turn them into protruding rivets, so I suspect it is not relevant to the topic of installing flush head rivets flush in dimpled or countersunk holes.
     
  6. Jul 25, 2019 #6

    geosnooker2000

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    So then, basically, if I wanted to do flush rivets on all the skins for aerodynamic's sake, then I would change out the standard Harbor Freight riveter head to the Zenith head when I wanted to rivet the rest of the parts (interior, etc.) and not have to worry about dimpling/countersinking anything else, and use the same rivets everywhere.
     
  7. Jul 26, 2019 #7

    BoKu

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    You'd only do it that way if you wanted to do the oddball re-doming trick. It's just me personally, but the technique seems kind of hokey to me. I'd just use dome head rivets and not bother with the custom riveter nosepiece.
     
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  8. Jul 26, 2019 #8

    Turd Ferguson

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    If that’s the reason you’re doing it you’re wasting time.
     
  9. Jul 26, 2019 #9

    Pops

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    I have a good supply of the pulled flush rivets bought from Zenith for the Zenith 600 project. I use the 3/32" flush rivets on the doors of the JMR riveting the aluminum door skin to the 4130 tube door frame. I dimpled the holes in the aluminum skin and then used a cheap rivet puller to pull the rivets and they all came out great.
     
  10. Jul 26, 2019 #10

    BoKu

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    Not necessarily. The aerodynamic benefits are small but measurable.

    The real benefit of flush riveting is that it makes it so much easier to paint, wash, wax, and polish the exterior surfaces.
     
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  11. Jul 26, 2019 #11

    geosnooker2000

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    And, although I'm no expert, I'll be the first to admit, I read somewhere some Military or NASA study back in the 40s determined that going from domed rivets to flush on some particular airframe lowered the hp requirement to maintain a particular cruise speed from 182hp down to just 82hp. Now that is a fuel savings and range lengthener I can get behind.
     
  12. Jul 26, 2019 #12

    Pops

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    I use flush rivets as much as I can. The little extra work means nothing since I'm having fun. It's like the work of kissing your wife.
     
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  13. Jul 26, 2019 #13

    karmarepair

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    I've been meaning to make up some test panels and borrow your Break-A-Tron so see if the Heintz re-doming trick actually does anything, but life keeps getting in the way.
     
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  14. Jul 26, 2019 #14

    Turd Ferguson

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    I’ll take that bet. At the end of the day you won’t “notice” any difference.
     
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  15. Jul 26, 2019 #15

    TFF

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    For looks, I can understand. The rest of the airplane is not set up to make a difference. You could always do the Mooney or Russian designers thing by just doing the leading edges about a third back. Zenith with their home domed rivets always makes me wonder why? Rivet joints if designed right have the rivet fail just before the metal. The idea is it’s much easier to replace a rivet than the skin or bulkhead.
     
  16. Jul 26, 2019 #16

    Mcmark

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    Boku PM sent.
     
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  17. Jul 26, 2019 #17

    pictsidhe

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    Supermarine built an early Spitfire entirely with countersunk rivets. They then progressively glued split peas to the flush rivets to simulate domed ones and measured the change in performance. After that, they built Spitfires with a specific mix of flush and domed rivets...
     
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  18. Jul 26, 2019 #18

    BoKu

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    One of their general findings was that on the aft part of the airframe, there was relatively little performance penalty for lines of protruding rivets aligned with the slipstream. But I don't think the WWII-era RAF spent much time painting, waxing, or polishing their airframes.

    Of course, the performance penalty was relative to the amount of extra time and resources required for flush riveting, balanced against the impending onslaught of a ruthless horde of fascists led by an unstable dictator. Boy howdy I'm glad I didn't have to run the numbers on those detail design decisions.
     

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