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No experience with this, but I would guess it does. If the glue is in a hard solid film, it will transmit sound much better than a soft spongy mass. It's like making a guitar top out of polystyrene...

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"I am always doing that which I cannot do, in order that I may learn how to do it."
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I had a discussion recently with a local builder, David Pace in Baltimore, who builds classical guitars, about 1/2 double tops and 1/2 conventional solid tops. David said that his double top plates come out a little bit heavier than a solid wood top, and that he didn't think that weight was the key to what makes double tops different. He thought that the difference was the more isotropic nature of the top stiffness, with much less variation between along-top and across-top in the unbraced plate when the double top is used.

(Well, that had nothing to do with whether the nomex core should or shouldn't get filled with foam )

Damann's original tops simply had wooden spacer strips, which is probably not a great idea as the outer skins aren't uniformly supported as well as with the nomex core, but if isotropic-ness is the key, you could probably do an initial version that would simply be like laying up plywood - just use a middle layer of spruce or cedar or something with grain running side to side, and that plus the two glue lines should even things out pretty well. You could use balsa for the middle layer too.

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Jim Kirby
kirby@udel.edu

I'll have to try polystyrene for a top on my next cardboard guitar

Gorilla glue foam isn't exactly soft and spongy when it sets up, and at any rate I'm not sure how it would affect transmission or loss if embedded in an otherwise solid box frame structure. I imagine it's somewhat different from a sheet of polystyrene.

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Jim Kirby
kirby@udel.edu

Well I meant relatively soft! The glue I've used (Not gorilla glue, another make) is sort of softish when cured - you can dent it with a fingernail. I would just have expected that to increase the damping in the top, but again, I have no experience with double tops...

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"I am always doing that which I cannot do, in order that I may learn how to do it."
Pablo Picasso

https://www.facebook.com/FenskeGuitars

Jim Kirby wrote:
"I'll have to try polystyrene for a top on my next cardboard guitar "

Are you thinking of foam board that is used for mounting art prints? I've often wondered how this would work as well. It comes as thin as 1/16th inch and up to 1/2 inch thicknesses. I read that some is paper covered and some polystyrene faced. I've only used the white (paper faced?) stuff. Perhaps we could get together and knock out a formica bodied foam core topped instrument. It might be fun!

Foam has been used as a center core in sandwich construction for decades. You may laugh, but it would probably work fine, as long as you put it between spruce and not formica!

For that matter, has anyone tried balsa as a center core? End grain balsa was used for core material long before nomex.

Is anybody used dual component epoxy glue named "T88" ??

In the 'O Brien's videos he mentoned this glue as the best choice for double tops exactly because it's flexible and don't fill this cells of nomex. Also this glue must apply in very thin layer exactly because you don't want to fill this cells. This guy on video(on page 1 posted couple times) he apply glue on some kind of film, and after that spread on surface, and on this surface put first outer skin to collect glue, and after than new mesure of glue and same thing for nomex and iner skin.

Someone mentoned weight, yes weight is very important, you must measure weight of every peace of wood, and also measure amount of glue you apply.
Also need to use vacuum bag.

Point is to make top with 25-30% less weight, and also produce more vibration and response of the top.

Of course you don't must to to all this stuff and use this glue, but one thing is certain: more trouble you put in to, better top you'll get

When I deside to make double top, I'll try this complicated way

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Guitars are simply beautiful.

Yes, it could be! I've wondered about putting together a formica guitar, but I've been holding out until I could find a source for Pink Coral! For the top, a foam poster board could be a nice experiment - Lots of h^3 with not so much weight. Maybe that is the mysterious ingredient in Damann's third generation tops (see current thread on Delcamp)

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Jim Kirby
kirby@udel.edu

Interestingly enough I found a panel of that foam core art stuff with paper facing on both sides yesterday so I thought it would be funto measure its material properties just to see how it compares to spruce. It had a modulus of about 350000 psi which is about one quarter that of generic spruce but a radiation coefficiency twice that of a great piece of spruce! Didn't measure any damping properties but the panel did seem to have higher damping than spruce. It does make you think about alternative ideas though

Clay or someone, can you point to a source for 1/16" foam? I can't seem to find anything less than 1/8" on line.

Jim

edit: I do see something called Sintra, which comes in 1mm and 2mm thicknesses. It is aPVC-based foam. I'll try to test whether gorilla glue or epoxy eat PVC this weekend.

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Jim Kirby
kirby@udel.edu

Sintra PVC foam board comes in 1mm and 2mm as well as other thicknesses. It is available from Foamboardsource.com. They have 16 X 20 inch sheets, 1mm thick (10 sheet pack $25), 2mm thick (10 sheet pack $36) I haven't seen or used this product and don't know how it compares to regular foam board. It does claim to be light weight and ridged.

I have some prefinished, wood covered HPL (alpi ligna) that I built one guitar body (B&S) with that might make a decent looking guitar. A little different aesthetic than pink coral - which would also be a nice way to go.

I glue PVC bindings with super glue. Surfing the net I see where some people glue sintra with superglue or epoxy.

Another source for 1 and 2mm foam is rcfoam.com. Their foam is 'Depron', which is expanded polystyrene. It's probably lower damping than vinyl foam.

Also, check out the "Dave's Daft Experimental ESJ-2 Build" thread for a completely organic double top:

http://luthiersforum.com/forum/viewtopic.php?f=10133&t=37353

Thanks for that lead Greg. I was talking with another fellow very slow amateur builder at the BCGS concert by Goran Sollscher last night (his guitar is another story in itself) and I'm intrigued to follow this for a while, at least to the point of fabricating some laminates and doing standard testing. I've been lazy about doing any of that so this could be a good kick-start.

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Jim Kirby
kirby@udel.edu

Can I ask one off topic question? I don't know how to search here. I already made it 12 foot radius dish for my back braces, I made it with rope witch I stick it in to ground, and measure 12 foot and on the other end I put it pencil and scuare angle and draw a sample on the some univer, and cut it later. But I dont have space to do same thing for 25 or 28 foot for top braces?

Does anybody have sample of the 25 foot radius about 70 cm long??

I make it this way http://www.youtube.com/watch?v=FkdMyGGf6so

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Guitars are simply beautiful.

Google directions for making a "long compass". That will help you draw an arc of a circle without needing the space for the entire radius.

12' is a very tight radius for a full sized guitar back. I was making 18' radius backs for my somewhat small-bodied classicals (Romanillos plantilla) and even that looked like too tight a radius to me - I switched to 20'.

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Jim Kirby
kirby@udel.edu

On my Romanillos style guitars, really all my guitar backs, I use 15' tail to heel and 25 wing to wing. I made mine by drilling holes in a tape measure, went out in the yard, stuck a nail through one and a pencil in the other, drew the arc and cut on the band saw. Then I smoothed on a sander to the line. Perfect - no, good enough - yes!

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Waddy

Photobucket Build Album Library

Sound Clips of most of my guitars

thanks people, I already made it using photoshop for template, glue it to the univer surface cut it, and drill circle with router. I don't know for 12 ft is it to tight, I like guitars with big curves back, maybe I will bend this wood on bending iron little to be secure of any crack

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Guitars are simply beautiful.

[quote="Clay S."]Jim Kirby wrote:
"I'll have to try polystyrene for a top on my next cardboard guitar [:Y:]"

Are you thinking of foam board that is used for mounting art prints? I've often wondered how this would work as well. It comes as thin as 1/16th inch and up to 1/2 inch thicknesses. I read that some is paper covered and some polystyrene faced. I've only used the white (paper faced?) stuff. Perhaps we could get together and knock out a formica bodied foam core topped instrument. It might be fun![/quote]


I've used polystryrene (all different types of packaging) on cardboard guitars I make with my children. Those pizza base foam stuff works best. It works really well but in the hands of children, who are natural Pete Townsends, last a few hours. never mind, excuse for another pizza.

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We are all in the gutter but some of us are looking at guitars.

" I've used polystryrene (all different types of packaging) on cardboard guitars I make with my children. Those base foam stuff works best. It works really well but in the hands of children, who are natural Pete Townsends, last a few hours. never mind, excuse for another ."

Now that has entered the discussion isn't it time to bring in the goat?

Why not!

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Jim Kirby
kirby@udel.edu