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Tim, Is that the new sound system over Brad's right shoulder?   

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http://www.dickeyguitars.com

[QUOTE=zehley] ...My enginerdtuition tells me that the added strength of a laminated side
has something to do with the fact that you have two seperate grain
patterns that when bound together are better able to resist bending than
a single grain pattern. ...[/QUOTE]

I agree with this, weaknesses and strengths randomly add together between the two boards instead of going all the way through on a single board.

Tim and Brad this test was very nicely done and I thank you kindly for sharing the results.

I have a couple thoughts here:

It has always been rather obvious to me that a "double side" would have many benefits.

1)  greatly increased stiffness

2)  greatly increased crack resistance

3)  no need for any side supports be they tapes or sticks and the weight savings from that

4)  and most importantly, to me, why Ervin and others are able to get away with very thin top - the rim is so very stable that it does not move nearly as much with RH changes as a conventionally built rim.

Number 4 has been the biggest attraction to me of using double sides.

The one potential draw back for me was addressed here, thank you very much, and that is how much weight would be gained by throwing a layer of epoxy into the mix.  And I can see that the weight gain is mouse nuts......  And the percentage of weight gain could be further reduced when using more dense woods such as an outer layer of BRW and less dense woods on the inner layer over say a solid BRW side.

In addition when some of us use more massive linings such as the Fox style liners or even reversed kerfed linings with conventional sides this is not needed with double sides and very light weight linings can be employed since the sides are much stiffer unlined to begin with.

It is indeed extra work, requires a second set of sides and some epoxy, but the benefits clearly, at least to me, out weigh the detriment.

Nice job guys!

Thanks Jeff and all of the other engineer types.

I notice that, although the increase in thickness was negligible, there was a real increase in mass. Your engineer friend could calculate the effective Young's modulus of the two pieces of wood, and the change in E/rho, and get a more direct idea of the influence of epoxy saturation. It would also be very interesting to spread the same amount of epoxy on the outside surfaces of the non-laminated piece, to see what effect that would have. I suspect that the same amount of epoxy soaking in to the surface would add more stiffness.

Hesh wrote:
"It has always been rather obvious to me that a "double side" would have many benefits.

1) greatly increased stiffness

2) greatly increased crack resistance

3) no need for any side supports be they tapes or sticks and the weight savings from that

4) and most importantly, to me, why Ervin and others are able to get away with very thin top - the rim is so very stable that it does not move nearly as much with RH changes as a conventionally built rim."

Number one has been shown in this experiment, although another interesting datum would be the change, if any, in cross grain stiffness. Numbers two and three are the same thing, and make some sense, except that, as we see, there is a significant weight gain from the epoxy. Laminating might save some time over side splint reinforcement, but I doubt it. A seventeen percent gain in weight is not 'mouse nuts', unless the mice in your neighborhood are much better endowed than the ones my cats bring in. Why would less weight in the sides be a good thing?. Number four is not at all obvious to me.

It's likely that laminated sides would move less with changes in RH: that could easily be measured. However, the thickness of the top is more a reflection of the static load, prmarily of bridge torque, that it must withstand. In that respect any reasonable top-side junction is probably about as good as any other in resisting long-term deformation of the top, in my estimation.

I. too, think there are probably some advantages to laminating sides, but let's not get carried away. Experiments like this one are useful in showing us what really happens.

Al buddy the mice In Ann Arbor, because of the major research universities here, tend to be very well endowed......

Let me clarify please regarding the other points.

What I mean to say is that with double sides you now have the option of using two types of wood for a single side.  So..... with a less dense, lighter weight wood on either the inside or the outside weight could be saved over the weight of a single .090 solid side if this side was of the heavier variety i.e. BRW, Honduran rosewood, etc.  In addition less massive linings are required for side stiffness and no side supports are required either - again weight savings.

Once you add the weight of the epoxy but subtract the weight of heavier linings and sides supports and inner sides that are of a lighter material the true weight gain, if any could be calculated.

I agree with you about the forces that the top must endure but I disagree with discounting the impact on a top of a rim that moves because of RH changes.  We all know what a can happen with a dried out guitar.....  With a building style such as Ervin's, and he uses double sides, an expanding and contracting rim would greatly shorten the defect free life of a top I am sure.

On the down side, to me, is that this requires more wood, takes more time, is messy...... and probably does have a net weight gain.  On the up side is, well if anyone has the opportunity to play a Somogyi or McKnight guitar that will make it clearer.

I have been using and testing double and triple sides since taking Ervin's
class a year ago. I have used both epoxy and urea formaldehyde glues
and they have yielded similar results regarding strength and that bell like
tap tone. The UF glue tends to shrink some so I will probably stick with
epoxy in the future.

My biggest concern is crack resistance. I am not really seeing much of an
improvement. Off-cuts of the sides snap easily in my hands. I have
made one set of triple sides using an outside .050" layer and two layers of
.020" veneers. Turning the inner veneer cross grain obviously improved
crack resistance, and did not appear to result in any downsides. More
testing to be done before I settle on the optimum approach.

One benefit of the use of two layers of veneer is that they don't require
pre-bending, also it is widely available and VERY cheap compared to tone
wood.

Stiffening the sides does not necessarily make it possible to make the top thinner any more than eating carrots killed all those people in the world who died yesterday who ate carrots the day before.   Yes, they died; yes, they ate carrots.   Yes, the sides are stiff; yes, the tops are thin... So what?   The tops are thin on Flamenco guitars, too...and so are the sides, and they're mostly not laminated.

Time for Logic 101...

If its the epoxy impregnating the wood that makes it stiffer, why not just
impregnate a single piece of wood. Are you wasting more wood to make
two pieces to glue together? And the big question, if you are adding all
this epoxy into the wood, what affect does it have on the woods tone? It
may be stiffer, but are you killing or changing the tone of some sweet
zoot. May as well use carbon fiber or wood pulp mixed with epoxy. Then
you have an Ov.... Sorry, I almost swore.

After Ervin's class I am also laminating my sides and here are some of my observations.

1. Like Tim, it is truly amazing how much stiffer these sides are. There is 0 spring back after they come off the lamination mold. They fit in the outside molds perfectly.

2. The principal reason for stiffening the sides (using the ES method) is to reduce vibrational damping from the sides. As the theory goes if the sides are very stiff they will be more efficient about reflecting the energy of the top and back. (Think about ocilating a rope tied to a fence post, and one tied to a garden stake. The stake clearly absorbes a fair amount of the energy).

3. Cracks. If you are using nicely quartersawn sides for both the inside and outside they snap like twigs along the grain. I am not convinced that you get a ton of improvement here (but I suspect you get some). Ervin used to use a piece of Tyvek between his laminations but has stopped doing that (not sure why... I think Ray mentioned that he no longer feels it is necessary). However, I have tried using rift sawn and sometimes flat sawn interior sides and I have noticed that has made a noticable incrase in the crack resistance. (My testing method was snapping the off cuts between my fingers... so YMMV).

4. Liners. I am using the Fox capped linings. Again I am going for the maximum stiffness in the sides. I believe in the "lighter is better" (within reason of course) philosophy, but I believe in making it "lighter where it counts". Right? Wrong? I don't know, but I like the direction this is taking me so far.


Again like Tim I have noticed some real improvements lately employing some of these ideas, however I too have changed so many variables since picking up these things from Ervin that it is hard to isolate the value of each.

I do think it is worth trying this for yourself and drawing your own conclusions. I am pretty pleased with the results.

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

[quote="Rod True"]23% stiffer (based on deflection differences)

12% heavier

Not to bad at all I'd say.



That does sound pretty good at first, but, if you were only looking for increased stiffness, you could do it with less weight by just making the sides a bit thicker. By leaving a particular side 7 % thicker ( and, it would weigh 7 % more) you would get the same 23% increase in bending stiffness but with less added weight. This is because the bending stiffness varies as the cube of the thickness.

There may be other good reasons for using double sides, but it doesn't seem, based on this test, that they give you a stiffness-to-weight advantage compared to single sides.


Phil

The next test to do is with a bent piece. I wouldn't be surprised if the results differ. Bent laminations sure seem more stable than bent singles. I wouldn't be surprised to find that they are also stiffer for the same weight. If I get time, I may do a simple lay up. I'm pretty interested in this too but only if I can keep the weight the same or reduce it.

A layer of .010" carbon fiber on the inside would probably be the way to go if money was no object. Stiffness, stability, and split resistence would be hard to beat. The weight might be a factor though.

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http://www.chassonguitars.com

I know all you engineer types think I'm all wet, but I still think the stiffness of a pair of thinner sides is due to the incredibly high coefficient of friction created by the glue. When they are then laminated bent, it will be even greater, because curves create additional stiffness.

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Waddy

Photobucket Build Album Library

Sound Clips of most of my guitars

You are right about the CF, I made some test layups years ago that came out nice. But if you are looking for light and stiff, you can't beat a foam core panel. I made some test sides that I called "composite tonewood" that were stiff as 3/4 plywood yet lighter than regular guitar sides, veneer outside and inside a PVC foam core.

I don't remember if I linked to this before but it is an experiment that I did with bent lams. http://upnorthstrings.com/stiffness.html

At some point along this thread (or maybe another) someone mentioned the similarities between lutherie and boat building. There's relevance here, I believe.

In wooden boat construction, the strongest construction (from a weight perspective) comes from a technique called "cold molding". In this method, strips of thin wood are attached to the frame of the boat at a 45 degree angle to the keel, or the longitudinal axis of the boat, followed by a second set of strips epoxied to the first at a 45 degree angle to the first set of strips. Some builders go one step further and epoxy a third set of strips running lengthwise to the boat.

While not as thin as the 0.045 inch laminations that Tim is using for his guitar sides, the strips used in cold molding are very thin. Two or three layers creates a degree of rigidity and strength nearly equivalent to fiberglass. (Now there's an idea for ya, Tim!)

From the luthier's perspective, strength and rigidity are good things. Consider another advantage: since the grain of the wood in each layer runs at different angles, splitting of the whole is almost impossible.

To achieve this benefit, it would be desirable to have the grain of each laminate run at different angles to one another. 45 degrees is not necessary (unless you plan to sail your guitar to Hawaii). Even 10 degrees would be sufficient. Simply flipping the side pieces so they are no longer in a bookmatch orientation would probably be enough.

I just realized that I have been using a forbidden word: laminate.

I trust we all know I'm not talking formica or other HPLs used in lesser quality instruments. I'm talking wood. Like, in boatbuilding, when we speak of "bent laminate frames", not one envisions an avocado colored kitchen with matching countertops. Rather, people envision a curved bit of wood made up of multiple thin layers of wood bent to a form without heat or moisture. In the same domain, this is contrasted with "bent frame" members that are created by a steam bending process that carries the risk of "springback" with temperature and humidity changes over time.

So anyway, maybe the glue adds a bit of strength. Certainly the absence of shear on the glued surface adds strength. Strength isn't the issue here. Rather, the process creates a guitar side that is fully unstressed ("cold molded") meaning rigid and stable, and resistant to splitting.

And somewhat messy to create.

Please pardon my long windedness. This new site is awesome!

But if you are looking for light and stiff, you can't beat a foam core panel. I made some test sides that I called "composite tonewood" that were stiff as 3/4 plywood yet

Right! That's because stiffness is a product of the thickness of the piece. What's in the middle doesn't much matter, but rather, how far the two outermost layers are apart, is what matters. Remember the "rule of 8"...

So ... stepping out of the engineering for a moment, and looking more at the operations, are any of you guys using vacuum for this process?

I have been using clamping thus far, but I am thinking of switching to a vacuum bag.

Pros/Cons? General thoughts?

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

I think I remember Ringo posting a shot of a vacuum bag setup.

Looking at all the options, Rick's idea of a laminate of CF around the inside of a solid lining looks better all the time. You get much more bang for the buck with stiffness due to the laminate being so much farther from the outer skin. You don't get any split protection or cross grain stiffnes in the sides but that's easily remedied with run of the mill side braces. It sounded like a lot of work when he first mentioned it but compared to laminated sides?

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http://www.chassonguitars.com

For those who have been laminating sides for a long time: Does the added stiffness prevent, or greatly minimize, the distortion occuring in the soundbox over time (where the box is dipping around the soundhole)? Or for those who took Ervin's class, what's his take on it?

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

Brock said - 2. The principal reason for stiffening the sides (using the ES method) is to reduce vibrational damping from the sides. As the theory goes if the sides are very stiff they will be more efficient about reflecting the energy of the top and back. (Think about ocilating a rope tied to a fence post, and one tied to a garden stake. The stake clearly absorbes a fair amount of the energy).

Ervin told me he started doing it out of concern for brittle BRW sides.

My experience has been that a stiffer box does give more power.

As for the effect on top distortion, that would be pretty hard to prove but it makes sense. In fact, were it not for the sound hole, one could make the argument that, given perfectly rigid sides, a top's ability to distort would be limited by the wood's ability to stretch.

_________________
http://www.chassonguitars.com

On how people are doing it, I can't dish out names because I didn't ask to, but someone with very solid credentials who uses double sides (learned from Ervin) uses vacuum to do it. He has a 'bag' attached to a bottom frame so he doesn't need to move his mold once the sides are on, just puts it on a sheet of melamine which the frame/bag seals to. Also, using the breather material some of the vacuum clamping places sell has helped a lot to get a good seal.

I'm going to be using these on my next acoustic, as talking to this individual has me completely convinced. I'm going to be using an inside and outside mold with just the side thickness difference between them, pressing the outside over the sides and inside mold, and then putting vacuum pressure on the whole works (so they're held absolutely rigid in place with uniform clamping pressure).

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

My question did not concern top distortion. But rather sides' distortion. The box tends to distort over time as the neck block wants to meet the end block, so to speak. I am wondering if laminated sides, as an unintended effect perhaps, help prevent, or minimize that effect.

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

Laurent, isn't top distortion where the real problem is when sides distort though? Aren't we talking about the same thing or do have other concerns?

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http://www.chassonguitars.com

I do not think the top "makes" the sides distort. The sides distort for the same reason the top does: string tension. My thinking goes like this: if the sides are much stiffer laminated than not, can I rightly assume that they will offer more resistance to string pull? If yes, how much? Anybody measured something?

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

I've been doubling my sides, but just at the top 1 1/4" or so, since about 1996 when I started making my current jumbo designs. I got the idea from looking inside my 1988 Ramirez 1a. The sides are the "normal" .075" to .085" thick as is the doubler. Then I use reverse kerfing, and now I've added a layer of CF to the inside surface of the kerfing, and I've gone to CF binding. You want stiff and refelective? This is stiff and reflective...