Carbon Piano Hinges

Discussion in 'Fiberglass and Composite Boat Building' started by J.Byl, Dec 13, 2018.

  1. J.Byl
    Joined: Dec 2018
    Posts: 2
    Likes: 0, Points: 1
    Location: New Orleans

    J.Byl New Member

    Looking for some advice on a project I'm working on. I just finished building a new flush mount bow hatch for an old 1/4 tonner, Carbon/Glass and plywood core. It's mostly just for fun and to try something new. I tried using a live kevlar hinge, but I'm not very happy/ having some trouble with it. So, I would like to build a carbon piano hinge for it. I have some smaller ones that were pulled of a Russel Brown build, and I found a nice picture of the concept in a google search so I think I have a pretty good idea of what to do. My plan is to lay up 6-7 layers of 0-90 carbon, set a waxed stainless rod in the middle of the layup, fold the layup in half with the rod in the middle, and compress the lay up between two pieces of plywood covered in masking tape with the rod end just sticking out the edge. Once its cured, remove the rod, set a masking tape template taken from another piano hinge on top of the laminate, cut it out with a dremel, cut the piece in half, reinsert the rod and I should have a hinge that works... right? Any advice is appreciated. The deck has a slight camber that I'm not sure how to deal with, other than using two or three smaller hinges.
    Also, I understand I could just buy one for a lot less hassle, just trying to learn something new.
    Thanks for the help.
     

    Attached Files:

  2. upchurchmr
    Joined: Feb 2011
    Posts: 2,865
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    Location: Ft. Worth, Tx, USA

    upchurchmr Senior Member

    Looks very similar to one used on the AV-8B wing tip wheel door. Designed by McDonald Douglas company (no longer in business). The only difference is that the Av-8 design used a brass tube which is left in the laminate to form a bearing.
    If you don't have much curvature, it will still work when opening the hatch
    The ends of the hinge will just be more heavily loaded, but that amount of carbon will take quite a lot of load.
    The more you can cut the hinge fingers with a smooth rounded cut the higher the final strength.
    If you don't want to use the brass tube, using an aluminum rod for the hinge pin during curing will give you some clearance between the hingeline hole and the pin, if you heat the layup for cure.
    The aluminum expands, the composite cures.
    Upon cool down, the aluminum contracts, providing clearance to remove the aluminum, and also to reinsert the actual hinge pin.
    Any clearance between final hinge pin and the composite will also relieve "some" of the stress when opening the hatch.

    Just make the hinge straight. Then bolt it down.

    Have fun and let us know how it goes.

    As you can see in the above picture, the hinge will allow water to pass thru. Might not be an issue depending upon the rest of the configuration for the hatch.
     
  3. upchurchmr
    Joined: Feb 2011
    Posts: 2,865
    Likes: 89, Points: 48, Legacy Rep: 579
    Location: Ft. Worth, Tx, USA

    upchurchmr Senior Member

    Just remembered - it was not a brass tube, it was beryllium copper.
    Brass will have corrosion issues, beryllium copper might be expensive to find if you could at all.
     

  4. J.Byl
    Joined: Dec 2018
    Posts: 2
    Likes: 0, Points: 1
    Location: New Orleans

    J.Byl New Member

    Thanks for the response, I finished the hinge up tonight, it came out pretty decent considering how crude my techniques were, Russel’s looks much better :). I think it’s perfectly functional though. I ended up using brass rod for the pin(the last layer of my lay up was 6 oz S glass so it should be well isolated. My technique was pretty much as I described in the first post. Trickiest part was folding the lay up over the rod without messing the fibers up. If I were to make more hinges I would figure out some sort of plastic jig to help fold everything over and I would do a better job waxing the rod as it was a little difficult to remove. I ended up having to chuck the rod in a cordless drill and run it through some emery cloth to get a good fit. This one ended up being 10 inches long, I’ll get some pictures up next week after it’s installed.
    Thanks again, Jason


     
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