How to mount piano hinges in fully cored honeycomb hatch lid

So i am making fully cored hatch lids. I have molded the bottom skins of all my hatches to define the hatch lid bottom and a 1/2" trim on the edges. I plan to fill the inside of the lip trim with small cuts of corecell, then plan to core the whole inside of the hatch lid with 3/4 plascore pp honeycomb. The biggest thing i am left wondering is how best to attach my piano hinges into these fully cored hatches. I would like to avoid wood here if at all possible. The point in doing all this work was to make a fully cored hatch.

Does anyone have any good ideas on how to attach these things. My plan now is to jb weld a strip of 1/8 aluminum to the back side of the hinge mount inside the hatch. My plan was then to use closed ended rivit nuts and 5200 to seal all the holes for the inserts. Still, i am concerned about water intrusion into the hatch. I suppose i could install the rivit nuts into the skin before i glass and core it that way i could seal all the rivit nuts from the inside, but that leaves the rivit nut only gripping the bottom skin laminate. When i glass the tops, the glass will wrap the sides making them twice as thick and probably better for holding those fasteners. So it seems adding rivnuts first doesnt take advantage of gripping the whole layup. I dont know if drilling oversize hole and filling them with resin is the best idea. Seems the resin doesnt really bond to the plastic inside cells at all. Going sideway into it, i would get nothing but core, trying to seal plastic cells with epoxy. Doesn't seems like the best way to go about it. Im sure opening and closing the hatches would eventually lead to the plastic and thickened epoxy losing their bond (not sure if they ever really had one) and creating a path for water intrusion. Im hundred of hours into this project of molding lid skins and cutting cores so its to late to start over, but id love a solid way to attach piano hinges into the back side of the hatch lid that wont leak, and i really want to stay away from wood. Which was my reason for embarking on this fully cored hatch lid idea in the first place. Ive attached a picture of the molded bottom hatch skin
This gets cored with plascore and then i will glass all the tops, wrapping the sides. The piano hinge mounts into the back side of this hatch lid.
Any suggestions

 

If you care for this to last the typical method is to replace the core with something solid in the local area.

If you don't like wood, then lay up enough glass to fill the area between inner and outer skin.
It might work OK to fill the area with filled epoxy, but use good filler or the epoxy will break out easily.

Wood is the lightest method you have to keep the joint from breaking loose.
Just coat the wood with epoxy, drill your holes (oversized) for fasteners, after cure drill out the holes for the fasteners.

You are completely right to avoid putting rivnuts in one side skin. If there is no load it might work for a while.

 

You don't actually say what material the piano hinges are, but mention welding aluminium, so I infer that they are aluminium. Why not use S/S ones (piano hinges) and bond in place?

 

coosa board is what I used for my hatches just for this purpose.

 

Sorry, I may not have been clear in what I wanted to do here.

I am making cored hatches. The bottom skin has a molded 1/2" lip and sides that run up to the top height of the hatch. I plan to core these skins with plascore pp honeycomb. I will then glass the top skin once the hatch is cored. I want to mount the piano hinges on the back side of the huge so the hinge is mostly hidden. However this leaves me trying to attach in the plastic center of the honeycomb core thru only one outside skin since I am not going top to bottom thru both skins. Where I coulde grip from both sides or t but style from the back.


So the hinges are stainless steel. however The only non corrosive rivnuts I could find in the design I want were aluminum. I have also mentioned using 1/8 " aluminum flat stock inside the the hatch attached to the side as a sort of inside backing plate. I figured I could jb weld it to the back of the skin inside then Mabye glass over it. With the skin still open and uncored I could rivnut thru that whole deal gripping from either side, gob the inside with a epoxy cap to prevent water intrusion, then glass then too skin over the whole deal rivnuts included. Then just drill thru the glass at the rivnut point to clear space for screws. Still this leaves the gripping the first layup of the side and not the top skin which wraps later. I think with a glassed in backing plate this may be ok. Better water seal tho. The other way is to install the backing plate, glass it in, then core the hatch and do top skins, leaving rivnuts for last. This grips the rivnut thru the thicker laminate , but I worry about sealing the rivnuts completely , but I think Mabye filling as much thickened epoxy as I can get into the holes prior to rivnut installation, and Mabye sealing them with a bead of 5200 could keep the water out. I also thought about trying to make a glass backing plate I could just glue in inside. Other than that I can't think of any better way to anchor the hardware given it's orientation going sideways into core. Google searches provide no better ideas.

I suppose I could just bite the bullet and stick some wood in there screw straight into it, but to me it defeats the whole purpose of the fully cored hatch. This coose board you speak of. I've heard of it, but am not too familiar with it. Can u fasten directly into it. Mabye replacing the wood with coosa board would work?

 

When working with low density foam core, it's typical to substitute some high density core in the area, where for example, you need to place screws. The 26lb coosa you can screw to. notch out one side of your hatch where the hinges go and glue some coosa in there before you glass.

That is one way

 

So i did a little more research into the coosa board. Looks like a high density foam with a mat built in. Definatly alot denser at 26 lb per ft than the 5' density corecell i used for the hull. I am thinking i could just cut strips and core the back of the hatch where the hinges go w coosa, then core the rest w the plascore. I think that could work. Ill probably drill an oversize hole , fill with thickened epoxy or 5200 and try to glue in some kind of threaded insert for the screws, i dont like the idea of screws threads gripping any kind of composite structure

Unfortunatly i just purchased about $80 worth of rivnuts, so i need to figure out what to do with those. Mabye ill mount an aluminum plate to the hull to mount the other side of the hinge, or take a loss and sell them on ebay. Wish i would have known more about the coosa board before. Would have saved me a ton of time, research, money...but thats usually how this stuff goes. On another note, does anyone know a good cheap source for small cuts of coosa? Prob need 2'x3' but im sure it comes cut as 2'x4' which is fine, i can use small off cuts to make a few deck cleats.

 

Not sure where to get offcuts but you might try Eastern Burlap Trading Co. google them, they are the cheapest core suppliers I have found ... including corecell.

I hate the idea of screwing into composite as well but if you use the 5200 it seems to bond pretty darn good...maybe add a lid stay or air one of those air shocks to keep the hatch from slamming and it should last a long time.

Good Luck!

 

Well I got a 48x32 cut of 3/4" blue water 26 comin. Cost me about $140 shipped so not too excessive. I feel confident this stuff will work well for what I need it to do. Only thing left to do is figure wether I should drill and fill holes, use inserts or just screw right into the coosa board and bed screws. I would think inserts would be best but the ezlok ones I found are really pricy.

 

So one more questions about coring these lids. What should i use to glue the honeycomb core to the hatch skin, 5200, or thickened epoxy? Im using pp honeycomb and am trying to glue the clore to the skin, then ill do the top layups.. I will be replacing the core in the hinge mount area with coosa board strips. I figure 5200 woould be super tenacious and never separate from the hatch skin, but thickened epoxy cures way quicker, and might be stronger if not a bit more brittle... Although i am using a super flexible epoxy so probably no worries there. Any thoughts?

 

I am confused. Why would use use strong hinges? They look like little hatches. Hatches are usually unloaded when open, right?

You need something strong to keep them closed, not keep them in some specific place when open.

I suggest gluing sailcloth on the hatch and hatch opening instead of piano hinge.

I suggest rope instead of metal dogs, if that can work. Like the rope you will probably use to lock the hatch anyway. Remember that all articulations that go through a panel WILL leak. So don't do that, instead pull the hatch closed with some form of synthetic flexible material (like rope).

Simple, light, cheap, no leaks.

 

I'll be using southco latches to hold the lid closed. The hatch lids are bigger than they appear in the pics. The small hatches are 18"x23", the large ones for the dry boxes are 22"x38". They need to be pretty burly cause people will be walking all over them as there are 7 hatches in a small boat and the hatch lids essentially are the decks. This boat is a whitewater dory, think a drift boat with a sailboat like flat deck just below gunwale line.

As the the piano hinge, I guess I am using it for a few reasons. First, this is the typical method of hinge attachment on these boats for the better part of 5 decades now. That's a good enough reason for me. And piano hinges are strong. The lids don't weigh anything as they are glass and honeycomb. But I feel like the constant opening and closing of hatches will put the most wear and tear on these. Piano hinges seem like they offer the most support. I'm also putting the hinge mounting on the back side of the hatch lid so it's hidden, and recessed under the deck. I probably could have used smaller marine hinges as a top mount but I doubt they would be stronger or cheaper, and they have their own fabrication issues to boot. I also have already purchased the piano hinges, so it seems silly to change course. Fwiw I got coosa board to core the back of the hatch lid Inners. I cut some 1.5" wide strips of 3/4. I'll just drill and fill the holes for the mounting hardware. So be good and strong, saved me a lot of fabrication headaches with the whole mechanical fasteners gripping glass skins deal. Less backing plates, hardware, and extra junk. This way I built the same way I been, with denser core where I need the hardware.

I just need to figure a way to glue these precut cores onto these premade bottom skins at this point. The solution to the mounting problem has been dealt with. I think either method is fine, I'm just wonder if doing the 5200 would be more tenacious holding the core to the skin, like a core bond type material. I have a few extra tubes of 5200 Layin around I need to use anyways, so it's not gonna cost me any money either way I go. Just wondering if one is preferable to the other. Epoxy seems quick and easy. 5200 seems like a lot more work and time but a potentially more tenacious or flexible bond of core to skin. Still undecided, open to more opinions tho

 

Not sure exactly what you are doing, epoxy is I believe more tenacious than 5200. Plexus has adhesives that can flex and are as tenacious or more so than epoxy.