Official Luthiers Forum!

[QUOTE=Shawn]
I know there are schools of thought that the back should be a reflector and the top a rigid drum top but when extended to a classical guitar you end up with a hybrid instrument like a Smallman school design in which the rim and sides are MUCH heavier with the top paper thin...you get volume but at the sacrifice of tonal color and range.

[/QUOTE]

Interestingly Shawn I had the chance to try a number of high end classical guitars at a recent master class I attended. Among them were a Smallman which I could compare to my Aram. The Smallman was noticeably much heavier but also had greater volume, compared to my Aram. However, it lost a great deal of clarity and seemed dull in comparison, especially when a delicate touch was called for. The Smallman, in my view, wasn't the best lattice braced guitar at the class though.

With the low energy systems like classical guitars and lutes then the light weight body is in my view a must if you want to produce a wide colour range. With steel strings, maybe not so important.

Colin

_________________
I don't believe in anything, I simply make use of a set of reasonable working hypotheses.

[QUOTE=CarltonM]........ Apparently this avoids the tone-killing effect of cross-ply construction.[/QUOTE]
Is there any truth to that? I was thinking of making my next plywood side with the inner grain 90°.
Maybe I won't now!

_________________
"An adventure is only an inconvenience rightly considered. An inconvenience is an adventure wrongly considered." G. K. Chesterton.

Colin,

I really like Aram's guitars! I played one that a friend has and it is a really nice guitar...excellent volume and sustain but without sacrificing tone and even dynamic and balance across registers. Jose and Liam Romanillos speak very highly and fondly of him.

In the past when Kasha guitars were all the rage I played one of them as well (Richard Schneider's with the redwood top and back and BRW sides) and while the bass was incredible, the mid range was indistinct and the highs did not sing.

Each approach to building introduces its own voice and What I like about Kevin's Guitars is that there is no weakness anywhere in constuction, dimensions and voicing that take away from hearing the music being played.

Todd,

I am not an engineer, but I am a carpenter (I think that's a little like being a TV doctor ). A little wood engineering analysis would go something like this:

Typical rim construction would put the inside wood in compression and the outside in temsion due to bending it.

In Kens experiments with wieghts on top of the arches he put the outside (top of arch) in compression and the inside (bottom of arch) in tension.

What I a getting at here is that each surface experiences a different type of opposing force either tension or compression.

In one piece construction the fibers will slip over one another between these two forces as they are being held together with the woods cellulose. By laminating them with a glue (epoxy), and the glue being stronger than the cellulose, the epoxy minimises this movement of fibers between these two forces more than the celluose.

To magnify the effect of tension and compression sliding over each other do not put any binding material (any glue at all) between these two laminations (the tension lamination and the compression lamination) they really slide over each other and are very spongy.

Hope this makes sense

davidO

What about the process of laminated sides? I have read through this thread and have not come across any reference on the process, so forgive me if I have missed something.

Is the laminated wood bent AFTER the lamination, or before? I would suspect that the laminations would separate under the stresses of heat and steam?

before

_________________
Waddy

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Sound Clips of most of my guitars

[QUOTE=SteveS] [QUOTE=CarltonM]........ Apparently this avoids the tone-killing effect of cross-ply construction.[/QUOTE]
Is there any truth to that? I was thinking of making my next plywood side with the inner grain 90°.
Maybe I won't now![/QUOTE]
You know, I'm glad you asked, Steve. I probably should have written, "...the POSSIBLE tone-killing effect of cross-ply construction." Concerning guitar sides, some knowledgeable people say the-stiffer-the-better, and three-ply construction would most likely help accomplish that. Other knowledgeable people say the sides should be allowed to vibrate with the rest of the instrument, so too stiff isn't good. Other knowledgeable people say it doesn't make much difference either way. It's one of those "pick one and go with it" situations, so give it a try. I doubt three ply sides will ruin a guitar's sound, and who knows, you might like what it does.

Now, for multi-layer tops, I think you've gotta go with parallel grain. On the other hand, some people have used three or five-ply (cross-grain) backs with good results.

As with most things in lutherie, the skill of the craftsman is probably the most important ingredient.

[QUOTE=davidO] Todd,
I am not an engineer, but I am a carpenter (I think that's a little like being a TV doctor ). A little wood engineering analysis would go something like this:

Typical rim construction would put the inside wood in compression and the outside in tension due to bending it.

In Kens experiments with weights on top of the arches he put the outside (top of arch) in compression and the inside (bottom of arch) in tension.

What I a getting at here is that each surface experiences a different type of opposing force either tension or compression............
[/QUOTE]
David,
That doesn't really explain it because the outer fibers are in tension/compression just the same whether or not they are solid or plywood. What matters most is the distance those fibers are from the central axis. For some reason, plywood of the same thickness is stronger than solid wood.
The difference is the adhesive, so it must have an affect that accounts for this. I'm thinking that it fills in a lot of the small voids and pores in wood and that makes it stronger.
I don't know for sure, but that's my story, and I'm sticking to it!    

_________________
"An adventure is only an inconvenience rightly considered. An inconvenience is an adventure wrongly considered." G. K. Chesterton.

[QUOTE=CarltonM]
You know, I'm glad you asked, Steve. I probably should have written, "...the POSSIBLE tone-killing effect of cross-ply construction." Concerning guitar sides, some knowledgeable people say the-stiffer-the-better, and three-ply construction would most likely help accomplish that. Other knowledgeable people say the sides should be allowed to vibrate with the rest of the instrument, so too stiff isn't good. Other knowledgeable people say it doesn't make much difference either way. It's one of those "pick one and go with it" situations, so give it a try. I doubt three ply sides will ruin a guitar's sound, and who knows, you might like what it does.

Now, for multi-layer tops, I think you've gotta go with parallel grain. On the other hand, some people have used three or five-ply (cross-grain) backs with good results.
[/QUOTE]
I was thinking of just 2 ply, the standard outer and having the inner ply be 90 to that.


[QUOTE=CarltonM]
As with most things in lutherie, the skill of the craftsman is probably the most important ingredient.[/QUOTE] No need to get personal!       

_________________
"An adventure is only an inconvenience rightly considered. An inconvenience is an adventure wrongly considered." G. K. Chesterton.

[QUOTE=SteveS]I was thinking of just 2 ply, the standard outer and having the inner ply be 90 to that.
[/QUOTE]
Hmmm...I've always heard that even-numbered cross-plys are not very stable--they tend to warp--whereas parallel-grain plys expand and contract together, so they aren't subjected to uneven stresses. Once closed into the box, though, I don't know if it would be a problem.

I think that what makes these laminated sides so much stiffer compared to solid sides is that they are always somewhat cross grained. Even the most straight and vertically grained boards are almost never going to line up exactly grain-wise where they meet. Consider also that's in two dimensions: the grain on the face and the grain perpendicular to the face (the run out).

Compared to a single board where in the middle the grain always lines up exactly in both dimensions, a laminated board at worst will be as stiff as the solid board, and should be stiffer most of the time. I'm laminating my sides and I can confirm other's observations. The difference in stiffness is considerable.

I have had very good luck making laminated sides using a Fox style bender. I bend both inside and outside slats at the same time, then epoxy them in the bender between a couple of sheets of parchment paper. Really figured wood might need to be joined in a more rigid mold, but so far I haven't had a need to try.

I think the stiffness is just a result of gluing two pieces together, which keeps them from slipping against each other when you try to bend them.  If they weren't glued, there would be friction, but the two pieces of wood would slip against each other and bend relatively easily.  The glue keeps the slipping from occurring, therefore, stiffness.

_________________
Waddy

Photobucket Build Album Library

Sound Clips of most of my guitars

[QUOTE=Hesh1956]
So are you saying that you will stack the two sides and bend them at the same time?

And then what I am really fascinated with is that you are ding the gluing in the fox bender? Clearly you are using slats above and below but do you use more cauls than the two and the waist caul?[/QUOTE]

Hesh, that's right. I bend both at the same time and I glue them together afterward in the bender with no additional cauls. These boards are so thin (I'm going about .05" each) that they bend together beautifully.

I've been more active when bending these than I am with solid boards.... for example when I'm bending I use a small flashlight and watch the boards like a hawk for 15 full minutes under heat. If I see any gaps whatsoever between boards or between a board and the steel slat I take up the screw a little and re-work the blocks to get it flat again, then put the screw back down to get everything nice and tight. I might have to do this a few times during the course of a bend as little gaps pop up from time to time depending on the wood. Once I'm satisfied I let them sit overnight.

I fully expected to build a separate mold to glue these up, but they fit together so well that so far I haven't had to. I use a slow setting epoxy applied to both boards so that if they don't line up just right the epoxy should fill any gaps. Here's a close-up picture of what a wenge outside and padauk inside look like glued up in the bender:



If it doesn't look nice and tight like this anywhere down the length of the sides I'll take up the screw a bit and re-work the machine until it does, or else I'll have to build a mold with more support. So far I've done wenge, zebrano, quilted maple, and curly maple this way with no problems.

[QUOTE=Hesh1956]
So when doing the gluing, apply epoxy to both sides, do you drape the bender with waxed paper and then waxed paper between the upper slat and the sides as well?

BTW my fox bender has the ability to use two lower bout cauls, springs are installed and I often do this to avoid cupping. This would be a plus here right?
[/QUOTE]

Between the wood and the steel slats on both sides I have a piece of parchment paper which if memory serves is simply a silica coated paper. The point of using it is that epoxy won't stick to it and it keeps epoxy from dripping onto the steel slats.

I would think the more cauls you have the better, and better yet would be a solid mold with a bazillion clamps. My inherent laziness is the only reason I don't have a solid mold for this operation.

Steve,

The point that stands out for me in this discussion re: the neutral axis is that the two laminations are bent BEFORE they are bonded together. So I'd think DavidO's comment is right. If you look at the sandwich, you have tension-compression-adhesive-tension-compression. This may explain some of why these laminated sides are stiffer (of course, as I write this, I'm thinking that the whole reason of doing the heat bending is to minimize/eliminate the tension/compression at the outer fibers, so maybe this argument falls apart). So in the end, maybe the fact that the two laminations are different, with variable grain directions and stiffnesses is the main reason for the increase in stiffness. I've gotta believe that is real, given the number of knowledgeable people that have testified to that fact.

_________________
Gene

Politicians and diapers must be changed often, and for the same reason- Mark Twain

[QUOTE=SteveS] [QUOTE=davidO] Todd,
I am not an engineer, but I am a carpenter (I think that's a little like being
a TV doctor ). A little wood engineering analysis would go something
like this:

Typical rim construction would put the inside wood in compression and
the outside in tension due to bending it.

In Kens experiments with weights on top of the arches he put the outside
(top of arch) in compression and the inside (bottom of arch) in tension.

What I a getting at here is that each surface experiences a different type
of opposing force either tension or compression............
[/QUOTE]
David,
That doesn't really explain it because the outer fibers are in tension/
compression just the same whether or not they are solid or plywood.
What matters most is the distance those fibers are from the central axis.
For some reason, plywood of the same thickness is stronger than solid
wood.
The difference is the adhesive, so it must have an affect that accounts for
this. I'm thinking that it fills in a lot of the small voids and pores in wood
and that makes it stronger.
I don't know for sure, but that's my story, and I'm sticking to it!     [/
QUOTE]

No Steve, I think you almost got it but laminated wood is only stronger if
there is a curve laminated into the layup.

Take one piece of wood and saw it into three slices and glue them back
togeher flat. Now take an identical piece of wood and thickness it so it is
identical to the 3 sliced wood but minus the kerf width. These would be
similar in strength (modulus of elestacity). I did not do this experiment,
but from what I have read, it is true.

Keep in mind that changing orientation of the laminate layers changes
things. Interestingly, if the middle layer is 90 degrees to the face layers,
the bending strength along the grain is similar to a similar layup with the
middle layer running parellel. This is because the spacing of the two
"skins" largely determines the strength in the long axis.

So your three ply sides will be the best of both worlds. Strength from
cracking along the grain while retaining the strength from the both how
far the skins are placed apart and that bent lamination strength that we
can't define.