In the odd snatches of time while glue is drying or shellac is curing, I’ve been working on a new technique: building guitar rims using two slats of wood per side, laminated together to form a double-thick side (~.150″ thick). It adds quite a bit of complexity to the rim-building process–more steps and added time–but I’m really excited about the new acoustic possibilities. And one of my awesome buyers has agreed to wait a little longer for his instrument, so we can implement this approach to further increasing the contribution of his guitar back to the overall sound.

Why double sides?

Guitar sides with linings applied.
Two sides plus two layers of lining later, this rim is ready to be shaped to receive the top.

I decided to try this technique after reading the excellent book by Australian luthiers Trevor Gore and Gerard Gilet, “Contemporary Acoustic Guitar Design and Build.” I was especially impressed by Gore and Gilet’s discussion of the current state of thinking in guitar acoustics. I’m a believer in responsive-backed instruments; I build lightweight backs braced to encourage the plate to vibrate like a second soundboard. This complicates the acoustics, because the top and back and body cavity (air space) all need to work together harmoniously, or the efficiency of the system is hampered, and you get a run-of-the-mill, un-explosive, disappointing guitar. Gore is also a fan of the live-backed guitar, and he has found that one of the ways to improve the coupling between the top and back of the instrument is to take side vibration out of the equation as much as possible. He also routinely adds heavy weights to his instruments’ ribs to change the relationship of the top to back to body resonances.

Since I had a recent prototype guitar handy, I thought, “Hey, let’s see if this works as advertised.” It did, and even at the measurable rate he estimated (measurements are made by recording thunks on the bridge and the analyzing the recording using an audio tool like Audacity).

So in developing my client’s guitar, I decided that I’d add mass and stiffness to the ribs by laminating together two slats, and use laminated-in-place solid linings instead of kerfed linings. Basically, I’m building a lightweight, guitar-shaped banjo rim and counting on the mass and stiffness difference to dial down the response of the sides and encourage the top and back to communicate more freely.

The method I’m using

Added benefits

I’m pleasantly surprised by the increased stability of the assembled rim. I use a lot of maple, and maple really wants to spring back after bending, but these doubled sides are rock-solid. Once they came out of the vacuum bag, the doubled sides were locked in shape, and I didn’t have to wrestle them into the form to keep their shape. I expect this to take some stress out of the completed instrument body, too.

An unforeseen advantage is that when you’re using two slats, you can make each slat thinner, which is great if you’re using difficult bending woods, like maple. I used .075″ slats rather than my typical .085″ with this sugar maple, and the improved ease of bending and smoothness of the resulting bends is noticeable.

The whole rim, and especially the solid linings, look very cool. I’m shallow, I know, but I want my guitars pretty inside and out, and this finished rim is very clean looking. It looks like the inside of a violin!

5 thoughts on “New technique: Double Sides

  1. Hello,
    I’m Jeff Jung of Korea luthier.
    Sorry, I can speak english a little.

    I’m making the guitar and ukulele in Korea

    I find laminated side data on this website
    So, could i ask a question?

    1. what is the name about vinyl (plastic) ?

    2. what is the thickness about laminated side?

    3. how to choose the vacuum press?

    Thank you
    Best Regards,

    JEFF

    1. Hi Jeff-

      Your English is very good. 🙂

      I bought the vacuum bag (I chose the polyurethane version) from this supplier:
      http://www.veneersupplies.com/categories/Vacuum__Press__Items/Vacuum__Bags/
      More information on polyurethane vs vinyl bags: http://www.joewoodworker.com/veneering/polyurethane%20vs%20vinyl.htm

      The total thickness of my sides is about .150” (about 3.8mm). Each layer is .075” (1.9mm); I use two layers.

      I don’t have much good advice on choosing a vacuum press. I used an old refrigeration compressor as the vacuum source in my setup. (I built this support system around the pump: http://www.joewoodworker.com/veneering/EVS/concept.htm). There are many styles of pumps available—some of the refrigeration ones are good, but others apparently wear out really fast with this usage.

      Let me know if I wasn’t clear enough in my responses.

      Best,

      -David

  2. I have decided to try double sides on my next build. I have read the same ideas about the stiffer sides. It makes sense to me, but -proof is in the pudding, so we’ll see. I also know that several of the top Spanish builders use laminated sides on their top models, and of course John Bogdonavich in his book. From a practical point of view I think it will reduce any tendency for the side to twist or ripple, and just make it more stable. I’m not sure about the original titebond as an ideal choice, The original titebond is a fairly flexible glue. I would think something harder like weldwood plastic resin glue, epoxy or even hide, or fish glue, titebond recommends their supertitebond or their extend titebond for laminations – but I haven’t used either so I don’t know if they dry harder or more flexible. I use mostly fish glue in the guitar assembly (used to use hot hide but find the fish glue nearly identical and much easier to use). I do use the original titebond for a few things – the top and back joint, neck lamination and v head joint,…
    I’m a hobby builder, in Canada, built my first guitar in 1973 and now that I’m retired I figure I will be able to spend a lot more time in my shop;-) I had the great experience of going to Spain twice to study with Jose Romanillos (2003, 2006) and feel my guitars improved greatly. Although the best guitar I ever made is always, the next one;-)
    Cheers
    Bob St. Cyr

    1. Hi Bob,

      Thanks for your thoughtful comments.

      The stiffer, more massive sides work as advertised, at least as far as rim stability during construction and lowering the fundamental frequency of the top (which may not be desirable result on a classical guitar, but is great for my small-body steel strings).

      Lots of people laminate their sides using epoxy with success; I’m not a fan of epoxy, so I avoid it, even though it’s maybe the “best” glue for this task (no water, good gap filling properties, long open time). The downside of the TiteBond Original Extend that I’m using is its water content, which I worried would cause problems when mating dissimilar woods, but I’ve not seen any issues yet, even in very curly maples which can sometimes react strongly to the introduction of water. I’m pretty happy with the quality of lamination I’m getting with the vacuum press in combination with this glue (I’ll attach a photo of one of my test slices to check the joint). Animal protein glues also have the problem with the water content but don’t fill gaps as well as TiteBond, so I too considered using fish glue, but decided that the gap-filling property was important for a uniform joint. As to the flexibility, I think I’d rather have the glue creep than split because the inner skin and outer skin are shrinking at different rates… I hope I don’t have to find out about that the hard way! I really do like working with the double sides though—the build process is much more predictable especially cutting binding channels, because the sides stay square and the curves are very smooth.

      I’m deeply jealous of your trips to study with Romanillos. I understand he’s a great instructor and quite a character. He’s also cutting back on his teaching, so you may have hit him just at the right time!

      Thanks again!

      -David

      A close up of a laminated piece of side.

  3. Happy to be your first client getting the new tech! Lots of cool pics & I too like the smooth look of the solid linings.

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