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I have noticed that some luthiers doubled their ribs, making them REALLY thick.

What are the PLUS ans the MINUS of such a technique?

Not necessarily. Mine are 2 layers .040" thick, making them a bit under .080" when all is cleaned up. However, because of the glue, they will be slightly heavier than a single side the same thickness.
By laminating you add a lot of strength. Even at .080" my double sides are much stiffer than single sides the same thickness and hold their shape perfectly. All other things being equal, the consensus is that it helps gain a bit of projection and power.

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Laurent Brondel
West Paris, Maine - USA
http://www.laurentbrondel.com/

This is a really neat topic. I hope more have something to contribute. What woods are typically used in the inside layers? Do they usually purposefully match the top?

Mine end up around .08" as well. I am going for maximum stiffness in the rim. I also line most of my guitars with capped linings. This combination gives a rim so stiff that you could build the guitar outside of the mold. It doesn't budge.

I think there are a couple advantages to this. 1) Losing less vibrational energy from the top and back into the sides, and 2) over the long haul I suspect that the geometry of the guitar will hold up a bit better with the rim being so stiff. Time will tell on that one though.

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

The other advantage of laminating sides is when using a set that you know is crack prone, or is pretty but has some funkiness. Yet one more advantage is that it's much easier to bend any wood at .040" than at .080". Some woods, like EIR, I do not even pre-bend.

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Laurent Brondel
West Paris, Maine - USA
http://www.laurentbrondel.com/

How does laminating add stiffness?

Because you have glued two pieces together, creating a lamination, which resists bending more than solid pieces of wood due to the glue bond resisting the sliding of the pieces against each other. The physics of it may say otherwise, but in fact, it's true.

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Waddy

Photobucket Build Album Library

Sound Clips of most of my guitars

I think that the different grain direction of the two laminates may have something to do with it as well- even though both lams have the grain running 'lengthwise'.
Cheers
John

The minus is the extra work and time required to do the lamination. If you have to thin down rosewood or other gummy wood a lot it can cause sander gum-up.
I generally use yellow cedar for the inside layer, so it's not too much extra expense, usually.
The added stiffness (and crack resistance) is the big plus. Also, I don't bother with side 'braces', cloth tape and the like when I use laminated sides.

The first thing you have to decide is whether you think that thin, resonant sides/rims are important for good tone production.
Once over that step, the path is pretty obvious.

Cheers
John

So if I extend your theory to braces, can I get stiffer braces by laminating some spruce together? Just how much stiffer does it get?

John

That might be a different situation. If you are talking vertical laminations, then no, if you are talking lateral laminations then, possibly yes. I think part of the difference is that braces in their natural positon are relatively straight, and laminations have less impact. Sides are curved, and when you glue two curved pieces together you get rigidity created by the combination of the curve and the glue holding the laminates together. There are builders that laminate deeply domed backs that are multiple layers of high quality veneer. The resulting backs need no braces, they are so stiff.

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Waddy

Photobucket Build Album Library

Sound Clips of most of my guitars

It's not a theory, everyone using laminated sides will tell you that, as Brock wrote, you can build the guitar without a mold. Laminated braces are indeed stiffer (IME at least). But there, Larson style, I use a thin veneer (.060") of hardwood in the middle and reverse the spruce grain orientation. Laminated braces are also obviously heavier.

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Laurent Brondel
West Paris, Maine - USA
http://www.laurentbrondel.com/

since we came to it, apparte from being stiffer and heavier, what are plus and minus of laminated braces?

Does the fact that they are heavier help reducing the size of the braces?

How does it affect the tone quality? (if possible to answer )

If you're talking about using the same material and laminating it to make it stiffer - well it's not going to happen. If you're talking about something like the Larson Brothers did that's a different story. Why they did it, is a mystery- at least to me. I'm glad that they did though because it's a great example of someone not building the best stiffness/weight ratio that they could.



They would have needed taller solid spruce braces to be as stiff as the rosewood laminations but not much taller. Solid Spruce braces as stiff as the Larson composite would be lighter. You can make lighter braces that solid spruce if you used a material that's much much stiffer- like CF, but that's another story.



It's possible to answer if you take this to the limits. At one extreme you get a banjo, at the other extreme you get a solid body electric. In the middle it's hard to say.

John

Where is Haans when you need him?
John, have you built with laminated braces "à la Larson Bros"?
I built a few, and recently. At equal dimensions the spruce/RW/spruce lams are indeed stiffer than a single piece of spruce, if only marginally. I think, counter-intuitively, that their biggest advantage is in the added mass. The guitars (mine at least) are more powerful, with a very quick attack and fuller bass registers.

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Laurent Brondel
West Paris, Maine - USA
http://www.laurentbrondel.com/

I build with laminated sides most of the time and I don't think they are that much stiffer than a very well bent side (in most woods). I think they seem stiffer because they so completely hold the right shape. I use the lightest closely color matched wood I can for the inner side and try to keep it under .080 for the final glue up. I will adjust the outer layer thickness based on how well I think it will bend (cupping etc...) and how heavy it is.

I cannot comment on how it changes the sound of the guitar, when I made the switch I changed other things as well. I do it mainly as a crack resistor and to try to keep things as stable as possible.

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Burton
http://www.legeytinstruments.com
Brookline, MA.

To that point....

I always use laminated sides, and I DO think they are stiffer. However I have two styles of linings -- capped linings on all non cutaway guitars and Ryan A4 on all my cutaway builds. The linings also make a big difference. The capped linings are so stiff you can't flex the rim without fear of breaking it, but the A4 linings do have a bit of spring in them.

But overall, I do say that the laminated sides are stiffer.

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

Laurent, Your results for laminated braces(being stiffer but not greatly) is what I would expect.
Indian Rosewood, whilst having a much greater hardness (resistance to denting ) only has a MOE (stiffness ) about 10% greater than spruce.

As far as laminated sides being stiffer, I would consider that the main mechanism here would be the impregnation of the laminates with glue. For the thin sections being used, this is potentially quite significant.

I haven't built with laminated Larson Bors style braces.

I would expect them to be stiffer than an equal dimension single spruce brace but that's because Rosewood is stiffer than spruce. And of course the rosewood weighs more than spruce. It's also easy to show that you can get the same stiffness by just adding a bit of height to the solid spruce brace. I did the basic calculations of this on another forum a while back, I imagine I could find it if anyone is really interested. But to be clear, it's not the fact that the braces are laminated that they become stiffer, it's that rosewood has a higher Elastic modulus than spruce. All rosewood would be even stiffer.

Exactly why the Larson's did this seems to be lost to history. Some people like their guitars. As you demonstrate, some folks still use their braces. Still, solid spruce braces rule the day. I like the fact that what the Larson's did goes againist one of the big luthier myths, build with the best stiffness/weight ratio that you can. The Larson's didn't worry about that myth, and it worked out just fine.

John