Bonding composite top to aluminum tubing

Discussion in 'Fiberglass and Composite Boat Building' started by fallguy, Dec 22, 2020.

  1. fallguy
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    fallguy Senior Member

    Any advice for bonding a composite sandwich top to an aluminum structural framework?

    Using the aluminum for the faraday effect. Please no runaway strikes!

    just want to get ideas for bonding the aluminum to the composite and the entire thing needs to be light enough to carry by hand

    I expect the aluminum to be either 2" or 1.25" tubing.

    Basically about a 4'x4' framework under and composite above.

    tia
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    What does the frame consist of, round tube, square tube, open channel ????
     
  3. fallguy
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    fallguy Senior Member

    Round tube most likely. The top is slightly elliptical.
     
  4. Mr Efficiency
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    Mr Efficiency Senior Member

    I suppose pop rivets might crush thin laminate, but it does work with slightly thicker sandwich panels, just one skin, with soft alloy rivets, using a strap rivetted both sides.
     
  5. Rumars
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    Rumars Senior Member

    Drill a hole into the composite without piercing the outer skin, then bond in a piece of G10 tube or plate. The G10 can be threaded and you can use machine screws through the Al. The bonding needs to be done either with a jig or the actual frame in place, there is no wiggle room. Or you can thread the inserts after glueing them in.
    The alternative is to glue the panel to the Al.
     
  6. fallguy
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    fallguy Senior Member

    I think the glue is the way to go here.
     
  7. Mr Efficiency
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    Mr Efficiency Senior Member

    What sort of glue ? Epoxy ? Tricky business gluing aluminium. I would just locally thicken the inside skin, and pop rivet straps with soft alloy rivets, It is out of the weather, so shouldn't be a drama with corrosion. I can't recall having any trouble doing that, blind rivetting inside sandwich boats. Obviously load involved is the issue, but if you spread it around, reduces the risk. Gluing round tube alloy to a flat surface, I would not attempt, you could glass across it to create a strap that way, and trap it mechanically.
     
    Last edited: Dec 23, 2020
  8. wet feet
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    wet feet Senior Member

    I don't see any indication of what type of composite is involved.If it includes carbon then you need to be aware of the potential (!) electrolytic activity if there is any kind of electrically conductive connection.My simplest solution would be to degrease the metal and bond with a generous dollop of Sikaflex 221, thats not a mistyping error, as it will have a bit of flexibility and sticks tenaciously,while still allowing a bit of thermal movement.Other elastomeric sealants with good adhesion are out there.
     
  9. fallguy
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    fallguy Senior Member

    I think the way to go is elastomeric glue.

    I want to put the radar up there and possibly the searchlight.

    I think the way to go will be to bend the aluminum tubing for the elliptical shape; then a light glass and bond to it; then heavier glass on top.

    Or, I could laminate wood frames and inset them into the tubing matrix to enclose wiring.

    No carbon!

    The idea is to prevent death to a helmsman in a strike, so we will bond the top to an earth ground.
     
  10. wet feet
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    wet feet Senior Member

    If you put radar or any other electrical devices up there,won't they provide the natural route for a lightning strike?Unless you have some other structure distinctly higher to attract the lightning,it could get expensive, but expensive is better than deadly.
     
  11. fallguy
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    fallguy Senior Member

    It will need some sort of crossmembers as well to get an elliptical shape to match the cabin roof, but the top needs to hold weight like radar, so a cored laminate..
    I don't care if the radar gets hit. The reason for aluminum is pathway for a strike.
     
  12. gonzo
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    gonzo Senior Member

    You could bond it with 5200.
     
    fallguy likes this.

  13. fallguy
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    fallguy Senior Member

    I have several tubes of it and Black Mamba FG. Think I will use the 5200.
     
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