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I am just starting to think about the double tops, but I think you would want something under the rosette and at least under the bridge. I would put solid spruce there.

My thought was not to route where the nomex goes, but cut a middle part of the sandwich from spruce and lay it up between the outside plates.

But at this point I really don't have the first clue about double tops. But that is the direction I am going in.

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Brock Poling
Columbus, Ohio
http://www.polingguitars.com

I think the better way is to route out an area leaving the bridge and perimeter solid and then "fill" the inside with Nomex. IMO you want to have a reinforced area for the bridge and bridge pins as well as keeping the perimeter solid to keep it free from soaking up glue into the voids of the nomex when gluing up the bindings....

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Peter M.
Cornerstone Guitars
http://www.cornerstoneukes.com

You most certainly can do that, but I'm in agreement with the others that you want a solid area under the bridge unless you don't care about longevity of the guitar. There is a large torque in that area that will be trying to peel the top layer from the skin.
you could do this though.
skin/nomex core/skin and make inserts for the hard points prior to bonding on the 2nd skin. You can sand Nomex core but be sure to de-fuzz it before bonding.

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Jim Watts
http://jameswattsguitars.com

I've not yet built a double-top (but thought it through about 1000 times and have all the stuff ready), and have only just started my first archtop - but I think you might be OK under the bridge with just Nomex. Maybe you want the top skin a little thicker there - but with just down-pressure I think you'd be fine (no bridge plate needed).

You may not even need to carve that much - if you had a properly shaped dish, you could vacuum clamp the whole works using just a properly thinned top skin that would conform to the dish, and lay your Nomex in on top. But I think you need solid spruce around the F-holes, otherwise I think (as already mentioned) you could get lots of glue sitting in the open Nomex cells that could inhibit vibrations in the top.

Above all- you definitely want to have solid spruce in the area of the recurve, because this is where all your tuning will take place once the box is closed. You may even want to avoid laminating this area - I am just not sure how a 2-layer laminate would respond to the typical carving that this area undergoes (assuming you can avoid carving through the top layer and into the underlying layer).

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The member formerly known as erikbojerik....

I have some dumb questions. What is the purpose of a double top? I've heard it talked about but I don't really know anything about it. Does it eliminate the braces? What is gained or lost by using a double top?

If done right, it will have a better stiffness to weight ratio than a solid piece of wood. The execution determines what's gained or lost. If it's not done well it won't add any stiffness relative to weight, and if the new structure isn't taken advantage of it might not have any advantage over the solid top(s) it was made of.

There are 'double top' (ie: composite) structures that are stiff enough and light enough to work both without braces and as a soundboard, but the ones I can think of aren't tunable: once they're made, that's the sound you're stuck with.

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

I say give it a try! And post results of course...

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The member formerly known as erikbojerik....

Chris…how are you planning to form the top? To be more clear with my question, are you going to make a female mold of the top or a male mould of this underside/inside?
In either case it will be a challenge given the complex curvature of the plate.

As far as the bridge is concerned, there really isn’t all that much force being applied downward on the plate. The majority of the string tension is in the tail piece. I wouldn’t bother to put anything special under the bridge.

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Rich S

"The inconvenience of poor quality will linger long after the thrill of a bargain has been forgotten"

How thick was the veneer that you used?
I would love to see one or all of the veneered tops that you have done.

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Rich S

"The inconvenience of poor quality will linger long after the thrill of a bargain has been forgotten"

Yes, that is how I have been doing for a while. All you ever wanted to know about DT at
http://dunwellguitar.com

Alan D.

Chris,

What a great idea. I haven't built one of these so this is all just thinking out loud. The way I approach new concepts like this is to first throw away the book and start with a fresh pad of paper.

I think that if you did this in the same way that we veneered your quilt top over spruce it could work well. I wouldn't even think about recurve or anything like that at this stage. In fact I would be more likely to think that it wouldn't have one by design. Why would you need a recurve if the top is already as thin and light as possible? It complicates things because it doesn't apply. The guitar you are thinking about only resembles the traditional archtop. No need to feel like the same methods and considerations will even apply.

But to consider the edge joint, you may find that the edges are too stiff once you build the first one. At that point I would start thinking about ways to loosen up the edges. But to make a double top archtop plate with a solid area for recurve sounds insane to me (because of the difficulty). Make it thin and stiff and perhaps inlay a purfling strip like on a violin to loosen that joint. But I would think that tuning could be accomplished more with bracing. On my Dragonfly guitars the edges are very stiff. I do have a slight recurve inside the guitar but the tops are always very stiff and don't move much around the perimeter. They aren't D'Angelico's, you know?

I also wouldn't worry much about the glue getting into the nomex. The binding itself will do more to affect the top resonance I would think. There will be much more of it than glue.

The approach I would take is one of exploration and discovery. Without expectation you can find a whole new design and a whole new genre of guitar. Traditional methods might make this concept impossible to build. And you don't want to get stuck there or you won't be able to build something fresh and new.

And of course let us know how it goes. I love these experiments!~

~David