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Old 24 July 2009, 09:23   #1
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Plywood core joint

Hoping to start a bit of a project soon which involves a plywood core made into a box and then covered in glass.
Needs to be very strong though. So to those who have made their own consoles, jockey seats etc out of plywood and glass could you recommend the best joint for the corners and top of the plywood. Or will the fibreglass hold it all in places?
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Old 24 July 2009, 09:35   #2
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I may be wrong, but i think you will find if you use a couple of panel pins and some wood glue the fibre glass will then hold it all together. I am just thinking how strong hexalite panels are and theyre just .75mm aluminum sheet spaced apart by a honeycomb of material thats as thick as kitchen foil theyre strong enough for aircraft floors! i guess the strength is in the outer skins. have you thought of using something like foam/cellular material as a core to make it lighter?
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Old 24 July 2009, 09:46   #3
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I may be wrong, but i think you will find if you use a couple of panel pins and some wood glue the fibre glass will then hold it all together. I am just thinking how strong hexalite panels are and theyre just .75mm aluminum sheet spaced apart by a honeycomb of material thats as thick as kitchen foil theyre strong enough for aircraft floors! i guess the strength is in the outer skins. have you thought of using something like foam/cellular material as a core to make it lighter?

Cheers mate, yes I have thought about using foam. But I've had it confirmed off two very good sources now that foam wont be strong enough. I'm going to be using 18mm ply. I want to build a 10cm high box to raise the console up plus house the bottom of my fuel tank. So the strength is important.

My plan is to glass the sides on the box inside and out onto the deck. Then fit the top. So the joint between the top and side needs to be something that can slide together.
So do you think Stainless pins and wood glue could do it? Would make life easier!
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Old 24 July 2009, 09:50   #4
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i would say it would ! the glue joint if made with a good gap filling polyeurathane wood glue will be as strong as the wood!
you could always put some triangular webs of hardwood i the corners made from 2x2 cut down. it would be less radius to get the glass into the corner too.
jwalker should have experience of this?
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Old 24 July 2009, 09:57   #5
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i would say it would ! the glue joint if made with a good gap filling polyeurathane wood glue will be as strong as the wood!
you could always put some triangular webs of hardwood i the corners made from 2x2 cut down. it would be less radius to get the glass into the corner too.
jwalker should have experience of this?
That is a bloody good idea!
With 18mm being so thick I also plan to round of the corners to make glassing easier.
The console will be glassed over the box and on to the deck.

Hope I like it
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Old 24 July 2009, 11:28   #6
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Biscuits should allow you to assemble a strong wood joint in situ.

http://www.taunton.com/finewoodworki...t.aspx?id=2991

jky
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Old 24 July 2009, 11:45   #7
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Biscuits should allow you to assemble a strong wood joint in situ.

http://www.taunton.com/finewoodworki...t.aspx?id=2991

jky
Would love a biscuit jointer but funds wont allow. Thought about using my router to do it but I know I'll feck it up.
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Old 24 July 2009, 12:03   #8
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John,

Take a look at my thread of my build (http://rib.net/forum/showthread.php?...=super+student) ...somewhere in there you will find details of how I made my console by glassing over ply. I was using 9mm and 5.5mm ply and joined most of the corners by filleting with epoxy. With some of the right angle joins I used 1x1inch baton, stainless screws and that expanding wood glue stuff...its not coming apart in a hurry

For what you want to do, the 18mm ply will be pretty strong and if you make the join between the top and the sides by having the top on top of the sides (join underneath the bottom surface of the top...does that make sense?!!) then there will be minimal load on your joint. A carefully wood glued edge should suffice with the glass over the top as well.

When you glass over the ply, you will need to use the stuff I specify in my thread (I think its called G4) to help the polyester resin stick to the wood (unless you're going to spend lots of money and use epoxy resin to wet out your fibre glass). An angle grinder is very useful too for rounding edges and taking off cured bits of glass.

Hope that helps a bit, I can go into more detail if needed.

Tim
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Old 24 July 2009, 12:08   #9
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Actually, your main loads will probably be from people hanging off your console is sharp turns and heavy seas so you could screw 1x1inch baton round the inside of your joins to make them super strong. Won't make it much heavier and you won't need to glass the inside.
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Old 24 July 2009, 12:34   #10
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Your the main man Tim!!
I want to glass the sides to the deck first, both inside and out. So this means the top can only be fitted afterwards. The baton idea is sitting rather well at the moment then
I could make the box (the deck forms the bottom of the box) with the top on and then fix to the deck but this means only glassing the outisde to the deck. Which wouldn't be as strong?
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