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

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

Post by Clancy » Thu May 24, 2012 4:51 pm

I posted this over on UU, but felt you'd probably also be interested interest in it here.

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 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 Turner 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 uke 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.

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.
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Re: Gore/Gilet/ Concepts & Falcate Bracing in a Uke Build

Post by kiwigeo » Thu May 24, 2012 4:59 pm

Excellent rant.....
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Re: Gore/Gilet/ Concepts & Falcate Bracing in a Uke Build

Post by woodrat » Thu May 24, 2012 5:03 pm

Lovely Work Craig.....At least you dont have to bother with bridge pins!

I look forward to seeing more pictures of the Falcate Ukulele

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

Post by Clancy » Thu May 24, 2012 5:28 pm

woodrat wrote:At least you dont have to bother with bridge pins!
Actually John, my previous ukes have used the "string through the bridge into the body & tied onto a bead" method, so I allowed room for this in the design.

But I am going to "cop out" on this build and use a tie bridge :lol:
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Re: Gore/Gilet/ Concepts & Falcate Bracing in a Uke Build

Post by Trevor Gore » Thu May 24, 2012 5:41 pm

Nice work, Craig.

First, I know nothing about ukes, but I would say your braces are too big. If you have a good uke (of the right size) that you like, do the bridge rotation test on it and see what rotation angle you get then work from there to size your braces. As a check you could also do the EI comparison if you can find a suitable uke with predominantly longitudinal bracing. Another check is to scale things using the (inverse) cube rule for both longitudinal and transverse spans (central deflections for simply supported beams centrally loaded vary as the cube of the span). I suspect most of your thicknesses and brace heights might come down.

Finally, I know nothing about ukes...

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

Post by Allen » Thu May 24, 2012 5:43 pm

Excellent work Craig. I know Micheal had started on some ukes with Falcate bracing, but got side tracked with all the other projects he has on his plate. I look forward to following your progress.
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Re: Gore/Gilet/ Concepts & Falcate Bracing in a Uke Build

Post by Clancy » Thu May 24, 2012 6:05 pm

Thanks for your thoughts Trevor.
My last 2 concert ukes had 2 finger braces 3 x 5mm (peaked over the bridge plate & shaved to 2mm at the lower transvere brace and nothing before the tail side linings.)
I was very happy with the direction these ukes were going.
Then your book came along and I started thinking too much :lol:

I don't think I can reduce the footprint of the braces, so 3mm they will stay.
I will play with the brace heights once they're installed on the plate.
The 5mm I stated was to be from the transverse brace to the rear of the soundhole (where the traditional lower transverse brace would be), whereupon they will begin to taper off.
BTW, my secondary braces, if left full length to the linings, would meet where the traditional lower transverse brace would have met the linings.
Just trying to incorporate some of what is known to have worked into what I hope will work better. :D
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Re: Gore/Gilet/ Concepts & Falcate Bracing in a Uke Build

Post by Tod Gilding » Thu May 24, 2012 7:40 pm

Very Interesting Craig :D I'm Looking forward to following this build
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Re: Gore/Gilet/ Concepts & Falcate Bracing in a Uke Build

Post by Nick » Thu May 24, 2012 7:47 pm

I know nothing of Uke physics and have only just started on Trevor & Gerard's books but purely from an "eye ball' point of view, it sure looks pretty with those sweeping braces & I can see the lower bout having a great monopole response but as I say, I've no experience of ukes & fan bracing so don't know their response 'normally'. But please keep us up to date with this build, it could be a really useful reference topic later down the line :wink:
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Re: Gore/Gilet/ Concepts & Falcate Bracing in a Uke Build

Post by Trevor Gore » Thu May 24, 2012 7:58 pm

...oh, and one more thing...

remember I know nothing about ukes...

You can probably miss out the bridge plate (unless its already in...)

And did I tell you I know nothing about ukes?

(these ideas are coming from my experience with classical guitars)

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

Post by J.F. Custom » Thu May 24, 2012 9:46 pm

Nice work Craig. 8)

I'd been through the same line of thinking a few months ago. With respect to the number crunching, if I recall correctly, I think I came up with f=140 for Tenor and f=160 for Concert size. I know I tried a few settings and averaged over several samples to get the result, but I think that was what it was in the end?! May have been I settled with 135 and 155... I've been waylaid with other projects since so have not followed through and can't recall with certainty. I'll check when I get the opportunity - different computer!

Incidentally, I was getting very slightly different results in the calculations to the graphs in the books too. Even though it did not amount to anything relevant in "real terms", it was still doing my head in as to why. I actually found the solution by accident, at least for my issue. Perhaps yours is the same so try this -

When I started, I set up separate excel files for each calculation to get a handle on it all. So if I calculated the youngs modulus in one excel file, then punched those precise numbers/results into another excel file setup to calculate the target thickness, I would get minor discrepancies to the results in the book examples.

When I changed this system to an 'all-in-one' excel file where all the calculations referred to previous cells that calculated the necessary data from start to finish - bingo; results were spot on to those in the book! Now I have one file set up so I can just punch in the timber specifications in each required cell and the setup calculates all the youngs modulus and the target thickness (for that piece of timber) whether to be used in a classical, steel string or ukulele. Does this explanation make sense to you?

Anyway, I figure it must be some internal rounding error or similar. The numbers on screen by the way, do not appear to be any different to those I was manually punching in - yet the resulting answer was very slightly different. Go figure. :?

As to the Falcate ukulele... I'll get around to that too. I was wondering on such a scaled down instrument with very little string tension, whether all the bracings were necessary? I had thought perhaps of omitting some in the redesign, but I have not got that far yet. I have current commissions first and a new baby due in coming months, so it may be a while off yet I'm thinking! :roll:

Good luck and I look forward to seeing your results and assessment of same.

Jeremy.

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

Post by Clancy » Thu May 24, 2012 10:20 pm

Excellent.
Now we're getting a pool of thought & information! :cl
It looks like our number crunching went in the same direction Jeremy. Cool. 8)

Trevor, unfortunately I don't have any 'good' ukes to measure or compare.
(If I did I'd start taking samples of their frequency spectrum to build up a reference library :roll: )

I have however reviewed some photos of my last ukes.
Jeremy, my thoughts with the secondary (and minor little horizontal) bracing is that they replace, in a superior manner, the stiffness and reach of the large bridge plate.
They will, of course, be a much lower profile than the main braces.
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Re: Gore/Gilet/ Concepts & Falcate Bracing in a Uke Build

Post by Trevor Gore » Thu May 24, 2012 11:14 pm

For those who have wrestled (or will be wrestling) with the numbers, check out this thread:
viewtopic.php?f=33&t=3626#p43983 which explains where some of those small variations may have come from. Rounding errors can introduce some minor errors too, and ill-conditioning in Excel can produce some huge errors, even though your coding may be technically correct.

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

Post by Clancy » Fri May 25, 2012 10:12 am

OK. After adding to the 'discussion(?)' on this over at the UU forum, I think I can put into words what I was seeing as I laid out the bracing.

The resistance to string pull on a more traditional bracing scheme (excluding the top itself) is undertaken by the lower transvers brace and, too a much lesser extent, the finger braces north of the bridge plate.
The lower transverse brace, while nicely chunky, is oriented 90deg from the direction of force.
It also effectively kills any chance of good vibration north of it.
The only thing that makes it effective in it's role is it's size and that it is (should be) anchored into the linings. Oh, and the comparatively lower string tension of a uke. (David Hurd suggests 33lbs [15kg] for a concert uke)

Looking at the main falcate braces north of the bridge, the orientation is closer to the direct string pull while the weight should be close to, if not less than, that of a lower transverse brace.
They also free up the soundboard to the upper transverse brace.

The way I see the large bridge plate I use on the more traditional bracing is that it adds a high degree of cross grain stiffness right accross the lower bout, something that has proven to be a good thing in a good sounding uke.
It may also 'spread' the load from the strings and, therefore, the vibration excitation.
However, it must act as a resistance to the development of the different modes. It is, after all, just another (albeit thinner) transverse brace.

By making use of secondary falcate braces (as opposed to removing them from the design) they can act as the cross grain stiffneners required, spread more evenly over a larger area of each bout, but without the mode restriction of a large bridge plate.
The difference in weight, if done properly, should be negligable.

I don't feel comfortable not having any bridge plate.
It seems to me that, even with the lower string tension, the bridge area still needs the support against long term failure that a bridge plate can give when done properly.
I intend to only use a layer of carbon fibre weave - no additional wood laminate over it.
The bridge is 3" x 0.75" (again, from David Hurd)
The plate will extend Nth & Sth of the bridge by about 5 mm at the peak of the curves.
It is less than the length of the bridge, butting up against the secondary falcate braces.

Just my thoughts.
Let me know yours.
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Re: Gore/Gilet/ Concepts & Falcate Bracing in a Uke Build

Post by liam_fnq » Fri May 25, 2012 1:25 pm

very interesting stuff Craig, I look forward to the progress.

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

Post by Trevor Gore » Fri May 25, 2012 1:40 pm

Did I say I know nothing about ukes?

There are a lot of classical guitars out their with strings pulling a lot more tension and no bridge plate.

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

Post by liam_fnq » Fri May 25, 2012 5:00 pm

Some of my thoughts: (I stand to be corrected).*

For string through bridges I use a hardwood bridge plate to help resist the string knots/beads from chewing up the top wood. For a tie bridge you could probably go with a spruce bridge plate or none at all. A string through bridge transfers the force to the underside of the top and you could therefore reduce the bridge foot print and therefore weight. Of course the weight of the required bridge plate may tip the scales too far. A bit of simple maths will tell you if it's worthwile.

My cedar tops are down around the 1.8mm for a concert. That's with two fan braces. Can you do up a conventional top as a control and do all the weight, stiffness, deflection etc to see what you're saving/gaining.

Great thread BTW, oh, and make sure to ignore the luddites.............

*Disclaimer: I haven't read the books.

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

Post by Clancy » Fri May 25, 2012 5:47 pm

Can you do up a conventional top as a control and do all the weight, stiffness, deflection etc to see what you're saving/gaining.
Great idea Liam - should have thought of it myself :roll:

Great thread BTW, oh, and make sure to ignore the luddites.............
Thanks mate, I seem to have run into a pack of them over there.
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Re: Gore/Gilet/ Concepts & Falcate Bracing in a Uke Build

Post by Allen » Fri May 25, 2012 6:00 pm

On some models I use the CF bridge plate that David suggests. And on concerts even dropping the fan braces completely. Those instruments sound great. So it really doesn't take much in the way of bracing on a concert. Our Pineapples only get a small bridge plate too. And they are loud little buggers.

I've not read the books either, so take what I say as just experience with conventional bracing. As well the lattice bracing that I use balsa and CF tow is such a different animal that I would not dare to compare the two.

I would love to have the time to explore this concept, so look forward to your results.
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Re: Gore/Gilet/ Concepts & Falcate Bracing in a Uke Build

Post by endgrained » Sat May 26, 2012 4:45 am

I'm so pleased that I found this thread today. As much as I love the UUF, that discussion seemed to miss the point: a discussion. I'll be quiet now and just follow this. Thank you.

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

Post by Clancy » Mon May 28, 2012 8:54 pm

All braced up.
Primary braces 3 x 3.5mm
Secondary braces 3 x 2.2mm
Tried to go without a bridge patch but wussed out at the last minute. :roll:
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First impressions - F#@k that's stiff!!
Not having worked with carbon fibre before, it's nice to get a feel for what it can do.
Then I took a breath and started flexing the main braces, holding at the bridge area and the fish tail at the end.
It actually feels pretty good.
Flexing between the primary & secondary, and secondary & finger braces, feels good also.
My gut feeling is that the secondary braces are too stiff, but what the hell do I know - this is like when built my first instrument. :lol:
Oh, and I can't get any flex in the finger braces, but then they're really short.
Maybe they don't need the top layer of fibre. I'm tempted to remove it.

Anyway, onwards we go.
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Re: Gore/Gilet/ Concepts & Falcate Bracing in a Uke Build

Post by Allen » Tue May 29, 2012 5:52 am

It's the same thing I thought when I did my first lattice braced top Craig. It's absolutely amazing how stiff you can make a top with a little CF.

Looks interesting. And really keen to hear what you think once strung up.
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Re: Gore/Gilet/ Concepts & Falcate Bracing in a Uke Build

Post by Clancy » Tue May 29, 2012 10:20 pm

Knocked up some mounts for adding side mass.
Don't know if I'll actually be able to get my fingers in there, but if there's no mounts there's no chance at all of trying any mass loading.
This is screaming in the face of "light uke = great uke" convention.
The mounts themselves were just under 9g each (Qld Maple).
The total bracing weighed 5g (not including the soundhole patch)
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Re: Gore/Gilet/ Concepts & Falcate Bracing in a Uke Build

Post by endgrained » Wed May 30, 2012 1:05 am

It is my experience in the profession of clinical psychology that Luddites can be saved. This type of discussion is part of it. More important is lowering shipping rates to the US and only sleeping when we sleep so as to catch us in our most regressive moments very quickly. Haven't you folks noticed the "science is just an opinion not real religion" movement in the US.?

In all seriousness, I've written R.M. Motolla about the "guitar is not a ukulele" issue. I never understand more of that statement than "wrong idea". David Hurd had a chuckle over that one. Doesn't it suggest that the Gore/Gilet volumes need Craig's extension/application of their work as an eventual addendum. Come on, all of you guitar only builders have a scrap box labelled "ukulele" in the back of the shed!

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

Post by Allen » Wed May 30, 2012 5:45 am

When you post that picture those on the UU are going to have fits Craig.
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