Gore/Gilet/ Concepts & Falcate Bracing in a Uke Build

Warning: This is a bit of a rant.

This thread will only make sense to those of you who have read Gore & Gilet Guitar Design/Build books.
Sorry, but I’m not going to attempt to explain anything to those who haven’t read the books. (That’d be far too difficult a task to do here).

That said, in arriving at some target data from guitar data, I have made some assumptions. If you don’t agree with them then say so – it can only help us all.

Ok then.

First up, is it really worth doing??
Professional builders have proven that the standard fan bracing with bridge plate works well.
Actually, some have even proven the value of no fan braces when a large carbon fibre bridge plate is installed.
Installing a single piece of carbon fibre weave is a hell of a lot easier than making multiple bent braces & gluing them in with carbon fibre strands.
Is it a case of just re-inventing the wheel.

Three things swayed me to go ahead.
1: I know that Allen spent a considerable amount of time and effort successfully creating his lattice braced ukes.
2: The concepts of the bracing system, whilst intended for the guitar, should translate well to a ukulele – it’s the same physics right!?!
3: As Rick is so fond of saying – Stop thinking about it and JUST DO IT.

So after stewing for quite a long time on the info presented in these books, I decided it was finally time for action.

The bracing system is just one of the concepts presented by Gore/Gilet. An important aspect is being able to repeatedly obtain the same stiffness in a plate regardless of its individual characteristics.
This is achieved by varying the final thickness of different plates so that they all have the same stiffness.

I first set up the Plate Thickness Calculation (4.5-7) in Xcel.
The authors kindly include a table (4.5-3) of their own test data on various tonewoods which allows you to check that your spread sheet calculations are entered correctly & your answers are correct. (I found that there was a small margin of error between my determined values and the table’s)

Righto, time to apply all this to a concert uke test build – let’s call her Prototype 1.

Again, the author’s kindly include their target stiffness values (f) for both steel string and classical guitars.

So what is the target stiffness of a concert uke plate?
I don’t know either.
So here’s what I did.

Most of the experienced builders here have suggested using a top plate thickness of between 1.8mm (for hardwoods) and 2.0mm (for spruce). Obviously this is very general, but it served to give me a starting target.
I inverted the equation so that I could enter in a design thickness value of 2mm and get an output value for the target stiffness.
As my top plate is englemann spruce , I entered in the 10 different sets of values for englemann spruce given in table 4.5-3, using the body length & lower bout dimensions of my concert ukes.
This gave me a stiffness value average of f=175 (with a range of 159 to 189)

But this is giving the f value for a standard braced top.
By using a falcate bracing design I want to improve on the concept of top weight reduction without loss of stiffness (as Allen does with his lattice braced tops).
So I’ve arbitrarily reduced the stiffness value to f=150.

Out to the wood stash and grab the pre-prepped bit of spruce I intend to use for the top.
I used Strobosoft to find the Long, Cross and Twisting vibration mode frequencies.
Then weighed it & measured it.
Plugging all this back into the equation gives a target thickness for my intended top of 1.7mm

Seems to me like a reasonable place to start the build.

Now came the brace layout design.

This wasn’t simply a case of reducing the plan for a falcate braced guitar.

I drew up the concert uke top plate, marking in where the saddle will be, where the strings will anchor, the bridge itself (using David Hurd’s website info), etc.
Using the rules as outlined in the Design book, I laid out the initial brace positions then used a spline to form some relaxed curves. Checked things, revised, checked revised. You get it.

One of the things you will notice about this bracing design is the lack of a lower transverse brace. All string tension has to be sustained by the main falcate braces or I’m going to have a nice failure when strung up (which in itself isn’t a bad thing when you’re trying to gain new information).

How thick the braces be to stop failure? How high? How often do I see these questions on forums……..
Drawing yet another unsupported conclusion from the correlation between guitar & uke, I am going to use the book’s suggested 2 degree of bridge deflection under string tension…..and say it’s the same for a uke.
Even having decided this, I can’t measure the actual deflection until it’s built.
So I’ve arbitrarily decided to use 3mm wide & 5mm high braces with carbon fibre rovings top & bottom.
This will be my starting point for future efforts (assuming the thing doesn’t just explode).

Included in my design is a carbon fibre bridge plate.
Unlike a more traditional design, the bridge plate does not extend past the ends of the bridge. Instead, the secondary falcate brace ‘peaks’ are under the bridge ends.

The braces were made from 1.5mm strips of sitka spruce.
The main falcate braces were simply bent around a form and glued.
The secondary falcate braces were bent around the form with heat.
I glued them with Titebond and found no ill effects due to swelling or cupping. (I would have used hide glue but I’m struggling with it in Canberra’s cold climate - as opposed to Alice Springs where I first started using it).

And that’s where I’m currently at.
The rest of the body is built waiting on the top.
The neck is well underway.
I start a new day job on Monday so I’m probably going to lose a lot of workshop time initially, but I’m doing a 3 day course with Trevor Gore on June 9-11 & hope to have this knocked up for testing by then.

Remember, comments & criticism are encouraged.

Really hope this works, love the look of falcate bracing. Always interesting to see how far people can push lutheiry like this.

When I see threads like this I always remember what P.H. said a couple of years ago (Quote: "A guitar is not a Ukulele" repeat this three times every night before going to bed)..well it was something like that

Ken is right on, the guitar is not a ukulele, and to think like a guitar maker is a waste of time.

You are way over thinking this stuff and I've seen this bracing pattern before, like the kasha designs. You may have fun with thinking about this stuff, but in the long run you will learn none of it is necessary in building a good sounding uke, the kind everybody wants. IMO, if you want to figure out how a good uke works, make 100 of them using a simple pattern, the same woods and pay attention to what you are doing and why. THERE IS NO MAGIC IN FANCY BRACING PATTERNS!

A guitar is not a uke.
How true.
And I'm not trying to build a miniture guitar!

But they do share the same vibration properties of a bound, flat board.
So does any flat topped instrument be it a charango or an irish bouzouki.
They all have resonant frequencies that create the main vibration modes - monopole, cross dipole, long dipole, cross tripole, etc.
How these resonant frequencies interract, which are stronger/weaker than others, is what creates the distintive sound of the different instruments.
Spruce is not a 'Guitar' wood. It's a 'Tone' wood.

Trevor Gore's mathematical modelling is of a 'stringed instrument body'.
Whilst he then goes on to present real data for a guitar using those models is irrelevant.
He provesa direct correlation of measured data with mathematical modeling, thus giving a means to 'fingerprint' existing instruments and 'target' current builds.
I am simply starting to investigate how the dat measurement and mathematical modelling will apply for a concert ukulele.
What are the dominant modes?
What is a good target frequency for the fully coupled air resonance?
What is a good target frequency for the fully coupled top resonance?
What contribution, and at what frequency, does the back have to the top resonance?
It's not voodoo.
It's science & engineering.

I'm in the early days.
I've used mathematics to arrive at a benchmark (for myself) for top stiffness.
I've arrived at a bracing dimension benchmark (for myself).
After I've built 5, 10, 100 in this way I may change my target depending on what measured results I get when they're completed.

The bracing pattern is pretty, isn't it. Just wait till you see it shaped & overlaid.
But that's not why Trevor Gore investigated this style.
The concept is to isolate the long and short grain stiffness of the top, so by adjusting one you don't greatly effect the other (as you would with an X-brace).
In the uke I have been using a large bridge plate (that introduces cross grain stiffness), a large lower transverse brace (that effectively kills any chance of good vibration north of it), and 2 small & thin fan braces (which attempt to adjust long grain stiffness).
With the falcate bracing pattern, the main braces north of the bridge take the support of the string tension - both lighter and stronger (in the string pull direction) than the previous lower transverse brace. They also open up the top all the way to the upper transverse brace.
The secondary braces take the place to the large bridge plate - giving a greater ability to adjust cross grain stiffness and spreading the load & vibration more effectively.

There's a long way to go with this 'investigation'.
I've put what I'm doing in a post for those who HAVE read the the books and HAVE begun wondering.

I grant you, it may not work.
Or it may sound great, but more like a (dare I say it) miniture guitar than a ukulele. (sigh)
Or, after a few builds, I may be able to repeatedly target in on a loud, clear, responsive concert ukulele sound.
I don't know.
Yet.

through the eyes of a complete beginner, that looks like a really strong uke soundboard.

As David Hurd is fond of saying "It's hard to keep things simple"!

These books you are referring to, are built on ideas that have been around for years, I don't see a lot of absolute new information or improvements in guitar design. Smallman's lattice bracing is a radical departure from the norm and it works but at a price to the sound, which to my ear is more metalic and less woody. Some like it, some don't. This system on a uke would also work, but it would be a lot of extra work to get to the same place the uke occupies. Why would you do that? As an example, let consider the Martin O style uke. This uke sounds wonderful and it has two small transverse braces and a thin bridge patch. Do you think that this uke would sound better if it had a bracing system that met all the critira that you mention in a previous post? The bracing system you picture IMO is going to make the top extremely stiff and not allow the top to move much, if at all. Science and wood are not always the best play mates.

Regarding Science, new or old: Over the past several months I've spent considerable time digesting David Hurd's work and bouncing it off of him by phone. In the eighties I believe he owned some 300 pre 1930's ukuleles. His background as a scientist (National Science Foundation et al) was at the core of his instrument building. Just a few months ago he remarked to me that most of his instruments felt like a breech birth. Perhaps he was talking about that thin line between art and science where the wood resides. I do know that very well regarded guitar luthiers still send him a new guitar design (body) to test using the same methods he applied to ukuleles. He remains a great fan of Carleen Hutchins who did not build guitars or ukuleles.

Submitted very respectfully. Any error in this brief comment is mine, not David's.

BlackBearUkes said:

.... Smallman's lattice bracing is a radical departure from the norm .....it would be a lot of extra work to get to the same place the uke occupies. Why would you do that?

Click to expand...

Perhaps you should ask Allen. He seems to sell a fair few of them.

I applaud Craig for his path of exploring this bracing idea. If I wasn't so busy I'd be trying it too. And it's really the first good thread here in a long time that may give some of the pros food for thought. Much better than what pick-up should I use, or my finish looks like crap, now what?

Hopefully he'll get some data and comparisons to conventionally braced instruments and I know that he'll share is findings with anyone interested.

For the life of me can not imagine why it would seem to threaten anyone out there to the point of saying "don't bother". That's a completely boorish attitude, and not conducive to furthering anyones knowledge. If this idea is not for you, then fine. But Craig is not a newbie trying to reinvent the wheel. His work is very, very nice. He's taken the time to do some research and is willing to share his results with the luthier community.

I got a similar response from "pros" about lattice bracing a uke. Not on the ANZLF mind you, where members are supportive, and Aussies have no problem telling a wanker just what they think. They soon get the message.

And while I'll be the very first to say my lattice braced ukes don't have that "Hawaiian" sound, they do appeal to a different set of buyers. Just like resonators do. Yes it's more work, but so what? I charge a premium for it, and people are willing to pay. Just as they do for Eric Devine's Kasha braced, maginificent works of musical art.

My rant is over. Now I'm looking forward to what Craig works out.

I confess I don't really understand a lot of this stuff at this point but I have to say that bracing looks really pretty! I can't wait to hear what it sounds like.

Craig, this experiment of yours is very interesting and certainly will attract much attention here. Thanks for experimenting and being willing to share your results.
As a former researcher in vibration, system dynamics and control, I find this fascinating.

I am a little unclear on the goal. Is it a different sounding instrument? More volume? Or just to see what this bracing pattern does on a ukulele?
(I realize goals often change after obtaining results .)

Again, thanks for letting us see your experiment.

Good post! I agree with Doc-J. What is your goal with all of this? If the process is fun for you and you just like to think about things like this, then go for it. You are doing what you should be. If you are trying to make a great sounding uke that looks clean, plays well and is beautifully appointed then you may be on the wrong path. Either way, its your building and your time so do what you want.

I must agree with Duane again, the only way to really learn something is to do it many, many times until you can tweak it to the point of near perfection. That usually means picking a simple design and repeating until you know how you want to tweak it.

My only real point I want to bring up to the group is this: An instrument is a system and each part does its job according to its materials, design and the execution of the builder. That is why we often say no when people ask for seemingly arbitrary custom options. We don't want to do anything in the workshop without major research, design and development. The reason all of our ukes sound relatively like each other (despite the different tonewoods) is because we understand our system and each part of it. What seems like a small change to an outsider could have a cascading impact on the whole system!

I still say that for a concert ukulele that's a whole lot of bracing. Personally, I'm going in the opposite direction! KISS.

Interesting....but man that looks like a lot of bracing for a concert uke! I don't think you need to worry about it failing.
I hope you'll post a sound clip. I'm guessing it will sound like a ukulele

Some like the journey while others like the destination.

I think a persons build style should reflect their personality. The way you choose to build has to make you happy, or what's the point......we obviously don't do this for the money. People may wonder why I spend so much time on detail work.....I really don't have that much of a choice, my personality dictates how I build. As long as it sounds good, your price reflects the time invested, and there are customers willing to pay that price. I admire your scientific approach, but I must admit a lot of this is over my head. I am an intuitive builder, and I build mostly on feel.

On the bracing pattern itself, i agree with the others, it looks overbuilt for a concert. I use a simple fan bracing pattern, and i have been "tweaking" it for the last 7 years........7 years of adjusting the same simple pattern, and I'm still learning.

As with the other old salts on this board I am still trying to get my fan brace system right - Alaskan spruce or Hemlock braces with Swiss pine fronts, Swiss pine bracing with koa and mahogany; and hey, don't get me started with bridge plate material.

And to encourage you - since you do not do this for a living experiment all the best you can... you have the time to do it and it doesn't really matter if it goes pear shaped. I did my college thesis on Kasha's ideas and came to the conclusion that the thinking is quite spurious since the science behind it and all of these radial bracing systems assumes complete uniformity in an organic material. All the best with this.