Double sides

[Brian Evans]

I've come across two builders in the last couple of days that say they are using double - or even triple - sides on their guitars. Both are building flat top guitars, both say they want to take the sides completely out of the acoustic equation and force the top, or in one case the top and the back, to vibrate more by having very monolithic side structures.

They seem to be traditionally bending solid wood, then laminating two layers together. Side thickness is enough to allow kerfing to be eliminated. Is this now a new path that people are exploring? Is a traditional approach to side construction more about "thin enough to bend" than anything else? this would help explain interior cloth lining on sides, braces every couple of inches, etc.

Brian

[Barry Daniels]

I use triple sides, but they are still pretty thin, so I use kerfing (actually laminated lining). I think the stiffness that is added helps the top and back lose less energy to the sides. I bend the outside layer at about .050" thickness and then add two layers of commercial rosewood veneer. What else can I tell you about them?

[Brian Evans]

I think that with archtops where the back is arched, graduated and recurved to respond acoustically to the top the more solid sides could have big impact. One luthier said his goal was to fully engage the back in the "air pump" and braced the back in a manner to get it more involved. He bent the sides (which look normal thickness to me) at the same time in a fox type bender, so they ended up identical. Here is a link to the thread. http://www.acousticguitarforum.com/foru ... 651&page=2

Post 30 and 31 has the sides, you can really see the thickness in the last picture, and post 34 has the back bracing. He calls it a "live back".

Brian

[Gordon Bellerose]

I use triple sides, but they are still pretty thin, so I use kerfing (actually laminated lining). I think the stiffness that is added helps the top and back lose less energy to the sides. I bend the outside layer at about .050" thickness and then add two layers of commercial rosewood veneer. What else can I tell you about them?

Barry, does that method allow for different, lighter bracing on the top and back?
It does not seem to me that it would make much difference in that aspect, but I thought I would ask.

[Gordon Bellerose]

Another question Barry.
What kind of glue do you use for gluing the thin pieces together?

[Barry Daniels]

The laminated sides does not determine how I brace the top or back.

I have tested various glues including Titebond, epoxy, urea-formaldehyde veneer glue. And I settled on epoxy (West Systems with a chopped fiber additive).

[Clay Schaeffer]

"And I settled on epoxy (West Systems with a chopped fiber additive)."

Hi Barry,
I also use West Systems epoxy to laminate sides. Do you add chopped fiber (fiberglass ?) strands to build in crack resistance to the sides and eliminate side tapes? I have used carbon fiber cloth between veneers, but fiberglass threads might be lighter, cheaper and reasonably effective.

[Barry Daniels]

It is an additive made by West Systems (403 Microfibers) and is basically very short polyester threads. It does two things. It strengthens the glue but it also thickens the glue which minimizes bleed through. I usually apply a very thin coat of regular epoxy to the veneer to wet it and then apply some thickened glue to one side before placing the pieces together.

I am not sure how much crack resistance is added in a guitar side because the joint is squeezed down with my clamp setup resulting in a very small amount of glue remaining in the joint. However the added strength is definitely noticeable when casting up thicker parts. So it may not be sufficient to replace your fiberglass cloth.

[David King]

This might be a good clamping job for firehose. You can safely get to 60 psi which is a whole lot better than with vacuum bagging and it spreads the pressure evenly. Your fixture needs to be rugged because 60psi over the area of a guitar side adds up very fast I.E. 7200 pounds or so.

[Jason Rodgers]

This might be a good clamping job for firehose. You can safely get to 60 psi which is a whole lot better than with vacuum bagging and it spreads the pressure evenly. Your fixture needs to be rugged because 60psi over the area of a guitar side adds up very fast I.E. 7200 pounds or so.

I think I can imagine what you're talking about here, but please elaborate. Fire hose, inflated with compressed air, and some cauls?

[Barry Daniels]

I would agree that vacuum bagging pressure is insufficient for guitar sides. I could not get it to work.

[Mark Swanson]

Bryan Galloup uses a heat-sensitive adhesive material for laminating sides. He does in the bender, all at once. Both sides go in the bender, with the material in-between, are bent and come out all set.

[Craig Bumgarner]

The book(s) by Gore & Gillet discuss in considerable detail the effects of more massive sides and side mass loading. I laminate my sides with four layers, cosmetic .5mm veneers inside and out and two layers of cross grain 1mm poplar on the inside, 3mm total. Very rigid, probably impossible to crack from climate change. Straight WEST epoxy, no fillers. I use a clamp and caul system. For cutaways, I've made some specialty clamps. Can clamp up a side in about 10 minutes after glue application. Faster than vacuum to set up, plenty of pressure and no worries about power outages. I also use oversize linings to increase mass and rigidity between back, sides and top.

[Barry Daniels]

I have also gone to a clamping system but I use an inside form with lots of bolts and bars.

I would be interested in learning more about Galloup's approach if possible.

[David King]

There are plenty of thermoset epoxies the issue is finding one with the properties you want. Here's a run down of the brands:
http://www.compositesworld.com/articles ... -adhesives
Alderite is a good bet.

[Craig Bumgarner]

I have also gone to a clamping system but I use an inside form with lots of bolts and bars.

I use a somewhat flexible 1/4" plywood caul on the inside to help spread the clamping loads and a slightly concave cauls across the width of the side and a single clamp. These clamping cauls are 5/8" x 5/8" x 4". The concave insures good clamping across the 4" width with a single clamp. I use as many clamps (Jorgenson bar clamps, the smallish ones) as I can fit, probably about 20. Very quick to clamp up a side. Nice thing about this system is the only real effort is the mold itself. The clamping system can be used on multiple molds.

My cutaway clamp was necessary because with the shape, bar clamps get in the way of each other. Again, very quick and works well enough on different shapes that I only need one. It is pretty specific to my situation so I won't go into details, but if any one is interested, let me know.

[Randolph Rhett]

I laminate using vacuum bagging all the time. Not sure why you would need more pressure than what a vacuum bag will provide. I've seen somewhere on this forum a picture where the side laminates were bagged together and then the bag and laminates were formed in an inside outside mold pair clamped together with about half a dozen clamps. It seemed to work very well and I was hoping to give the technique a try.

I intended to give it a try as soon as I could make a well matched set of molds and a 6" wide bag for the laminating. I really can't understand how the bag wouldn't provide enough pressure to laminate the sides together.

[Bill Raymond]

I believe that this is how Ken McKay does them. He uses the vacuum bag for gluing pressure, then puts the bagged laminae into a mold to hold the shape until the glue has set

[Barry Daniels]

Clamping the waist sufficiently was my problem. I tried a form inside a bag and a single layer bag on a form. Neither worked well. The full vacuum bag clamped to the form is probably the best way to go.

[Bob Gramann]

There's a technique for veneering where you coat both surfaces to be joined with Titebond and let them dry open. Then, you iron the two pieces together. The heat fuses the Titebond and the pressure from the ironing closes all gaps. I did it to veneer a Laskin armrest per Kent Everett's instructions. Could that work here? I would try it if I were trying to laminate sides, but I'm not.