alternate plywood panel joint

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alternate plywood panel joint

Postby tonyj » Mon Jul 10, 2006 12:07 am

Sorry for the length.
I can't take credit for this joint--came across it a couple of weeks ago in a small boat mag called duckworks. I decided to give the joint a try using the dovetail template from my cheapo HF dovetail jig and a pattern following bit. I glued up the 11 ft panel of 1/8" luan for the first roof panel. Due to time constraints, I put the second layer on with just glue, staples and butt joint.
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I purposely did it pretty quickly to see how the joint would turn out without being too anal about the whole process. The router work is fairly quick (15 minutes or so per panel end, and I stacked two panels at once without problem), but you have to be moderately careful on the layout of the router template. If one was careful, they could incorporate a well made, interesting looking joint for long panel construction. The flaws in the joint will come from the accuracy of your jig and carefully moving the template accross the sheet. But I was startled to see that just a little careful layout, overlaying the template over the previously three or four fingers yielded a pretty good joint. The gullets (the bottom round valley) had gaps that could be filled with epoxy and filler, but with a little work, even those could be eliminated.

Important point--do not test fit the piece before gluing!!! You cannot get this joint apart without tearing the fingers up. Place the panel fingers on top of each other, apply the glue or epoxy and use a mallet and piece of wood to knock the joint together. The joint holds itself together without clamps, and can even be moved around--but go back and pound the fingers back together, especially on the ends.

I was surprised at how well the joint worked on the 1/8 thickness. My payoff was one long panel, and I didn't have to worry about the joint falling on top of a roof spar. A little bit of bow or cupping on my panels caused the fingers not to be completely flat. I smoothed the uneveness with epoxy and a little sanding. If I had just sanded, I would have gone through the veneer layer and exposed the core. I think the joint would adapt better for 1/4 inch and up where there is a little more meat to work with. Joint will not bend well, so don't use on a radius. I purposely bent a test piece to about a 12 inch radius before the wood around the joint broke. I will definitely give this joint another go before shelling out for 10 foot ply in the future. People are so amazed at plugs over recessed screws that this joint will have people thinking you are a woodworking craftsman.
Still graced with two eyes and ten fingers (due in no small part to luck!).

Just when you think a problem is solved, an uglier result replaces it.

tony
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Re: alternate plywood panel joint

Postby kirtsjc » Mon Jul 10, 2006 6:34 am

tonyj wrote:I can't take credit for this joint--came across it a couple of weeks ago in a small boat mag called duckworks. I decided to give the joint a try using the dovetail template from my cheapo HF dovetail jig and a pattern following bit. I glued up the 11 ft panel of 1/8" luan for the first roof panel.


Credit for the joint type be darned!

It is your willingness to try it, do it, and SHARE it that is more important around here!

THANK YOU!!!!
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Postby IndyTom » Mon Jul 10, 2006 7:08 am

Tony,

I agree with Kirt, I have been looking at ways to join plywood panels together for years and have never seen one quite a slick as that. Im thinking that a piece of mdf, some careful layout and you could come up with a template that would let you do the whole end of the sheet in one pass.

Thanks for sharing. I gotta go back to read Duckworks.

Tom
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My build thread:http://tnttt.com/viewtopic.php?f=5&t=36226

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Postby GPW » Mon Jul 10, 2006 7:51 am

Time to build that boat that fits on top the TD .... :D Thanks !!!!!
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Postby WhiteRaider » Mon Jul 10, 2006 8:36 am

Very, very nice idea. Thanks for sharing!

With this method, sourcing larger plywood is no longer an issue! This seals it, I'm going to buy a router.

Cheers!
Rob
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Postby tonyj » Mon Jul 10, 2006 9:42 am

Tom,

Great idea. A four foot ply or plastic template would make the routing process a snap. MDF might work, but I would be concerned with the template swelling from just humidity. I think I'll make one from ply or masonite myself.

Rob,

Glad to be the justification for a tool purchase! You can never have enough.
Still graced with two eyes and ten fingers (due in no small part to luck!).

Just when you think a problem is solved, an uglier result replaces it.

tony
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Postby Chris C » Mon Jul 10, 2006 10:16 am

Swelling caused by moisture obsorption wouldn't pose any problem. The same template would be used for both pieces and done pretty much at the same time (work session), so a change in size would simply affect both parts equally.
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Postby tonyj » Mon Jul 10, 2006 10:24 am

Chris, I was thinking the swelling might prevent the bearing on the bit from sliding into the template, or breaking the template fingers from a tight bearing fit. That only occurred to me because one of the slots on my cheapo HF metal template was too tight for the bearing to go all the way in, and I had to do a little machining on the template.
Still graced with two eyes and ten fingers (due in no small part to luck!).

Just when you think a problem is solved, an uglier result replaces it.

tony
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Postby Chris C » Mon Jul 10, 2006 11:14 am

Oh, I see. Hmmmmm! :thinking: Don't know a solution there. But I still think your joining method is pretty slick. I'll definately file it in my memory bank....................but I'd better write it down, my memory doesn't work so well any more. :lol:
Chris :D

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Postby Miriam C. » Mon Jul 10, 2006 11:30 am

Tony
Thank you. You can make posts like that as long as you want. Really good thing ya got there. That router is looking better all the time. :twisted:

Keep it up.
Miriam
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Postby WhiteRaider » Mon Jul 10, 2006 8:19 pm

Well, that did it. Your panel joint caused me to pull the trigger on another tool purchase. :D In addition to a new, groovy, super smooth Milwaukee orbital jig saw that I purchased recently, I now have a new router on the way.

I was having a hard time finding decent ply bigger than 8x5 so this technique will help and looks cool to boot.

For those who are looking for routers, Amazon.com has the Hitachi KM12VC plunge/fixed base combo on sale for $119.77 with free super saver shipping today. It was one of the router combos that has received high marks in the woodworking magazine reviews and one that I was eyeing. The price was too good to pass up.

Cheers!
Rob
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Postby tonyj » Mon Jul 10, 2006 9:16 pm

Rob--I think it is the teardrop builder group that is responsible for keeping our economy alive and kicking. It is our patriotic duty to buy tools to make stuff. You're only doing your part. :lol:
Still graced with two eyes and ten fingers (due in no small part to luck!).

Just when you think a problem is solved, an uglier result replaces it.

tony
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Postby Nitetimes » Mon Jul 10, 2006 9:23 pm

That would be really sharp if you could pick out some sheets that were pretty close to looking the same and splice them with the grain running lengthwise to the joint. Good job. :thumbsup: :thumbsup:
Rich


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Postby Thawley » Wed Aug 24, 2011 12:57 pm

This thread has changed my life.
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Postby angib » Wed Aug 24, 2011 4:21 pm

That's an excellent joint - not quite as strong as a good scarf joint but then doing a good scarf joint is really hard.

A nice feature of this joint is that it will have the same stiffness as the rest of the plywood, so if you are bending it around a curve it won't create either a flat spot or too much of a bend where the joint is.
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