[Drassk]

The wood science part is simple: wood isn't isotropic, it's substantially stiffer in one direction than the other. The difference between longitudinal and cross grain stiffness is huge. So, for stiffness to weight, the best use of wood in braces is to have the grain running down the length of the brace.

It looks like the CC guitars have carbon fiber inlaid into the 'braces'. That makes a certain kind of sense in that the 'braces' are just there to hold the CF in place, and so their grain direction doesn't matter so much.

Integral tone bars / braces are older than dirt, so the patent can't cover integral bracing in general due to prior art. I suspect what the patent actually protects is the idea of inlaying CF into 'integral' braces, and the particular pattern used.

[CyborgCNC]

So other than going down the discussion on who owns the patent etc (as i think this thread is not about that), I would think that with a quarter-sawn piece of spruce for example, the integral machined braces would do a good job. Probably not as stiff as a separate brace, but would that not be enough to brace the top, while at the same time providing better acoustical properties? In other words, sacrificing maybe some "bracing strength" for better tonality?

@rlrhett..can you dig up some of the discussion as to why this is not "good wood science" as you put it...

[Drassk]

The common opinion is that a lightly built instrument sounds better than a heavily built instrument, and that means using your material optimally to keep mass down. More mass means more resistance to vibration, and that means more energy lost to heat rather than sound production. Quartersawn bracing is also very stable structurally, with no tendency to warp or or expand non-uniformly. Place a regular guitar top on a cement floor and it'll potato chip up a couple inches across the grain in just a couple hours.

The good wood science is simply that across the grain wood is like spaghetti compared to along the grain in terms of stiffness, and it also tends to bend and warp across the grain rather than along it. If you've never held a thicknessed guitar top, you'll be extremely surprised. It's analogous to unidirectional carbon fiber sheet- you can roll it into a tube in one direction and it won't budge an inch in the other.

Archtops are much more forgiving in terms of mass in the top compared to flat tops and especially classicals, and some players might prefer a little extra damping for their sound, so it might work out in ways you wouldn't expect. Archtops also often keep all the bracing in line with the grain, which would make the integral bracing 'all benefits'. Johnny's sort of going that way with his design, where the bracing is mostly trying to stay in line with the grain.

You could do some calculations in some FEA software using the along grain and cross grain stiffness to redesign the height of the braces as they go along to account for the differing stiffnesses. On a traditional X brace, it would be substantially taller.

[CyborgCNC]

OK..so the tool paths are done, and it is looking good!

Now to start cutting some wood, and make chips fly at 120 IPM!!

LOL....

More to come.....

[CyborgCNC]

OK...SO here it is! Just came back from my shop where my CNC machine was running...

I am EXTREMELY happy with the results....the integrated braces look absolutely awesome!

As you can see, a few tooling marks after the finish pass, but a little sanding and that is that....will need to flip the body over and do the front next. This part took about 1 hour to cut, and I was running at 140 IPM..

I can also tell you, that the top in it's current form is absolutely alive! The tap tone rings like a bell....very noticeable pitch drop as well from the raw top before the cut.....again, now for the front, and some more tap tone tests again...

The braces are also about 1/8 larger than what they should be, for final tuning after the whole top is cut....we shall see...

More to come again....

:banana:

[Scott McCray]

:cheers:

Need the popcorn smilie...

[packrat]

Alright! Not such an idiot after all. Never saw any of the makers that are doing it, just some thing I've been thinking of for several years. Don't have the stuff to do it myself so thought I'd suggest it to some one here.

[Drassk]

That's awfully pretty, Spiro. How long do you expect the whole build will take? I'm really curious about this one!

[CyborgCNC]

OK..so the top is done....now we need to do the bottom, and this will take me a while, as I do not yet have the wood for that...looking for some nice tiger maple to use for it...but in the mean time, I will focus on tuning the top...As you can see, I also cut the F-Holes, and the top from the block of wood.

-So far, all I can say is WOW! Very pleased with the results. Tap tuning the top, the "node" is right about where you would expect it for a top like this...like mentioned, the braces will have to be shaved down a bit, but all the tests I have done so far, with the top in it's current raw form, I can not really hear any tonal differences, as if the braces where glued on separately. I also left about .01 on my drive surfaces, to accommodate for final sanding, so the top is actually a little thicker than final dimensions, but this has not made any difference in it's sound, or at least none that I can detect.

I will finish carving out the braces to final dimensions and sanding in a few days, and will report back my findings, but so far, the results are awesome!

LOVE MY CNC ROUTER!

:cheers:

[CyborgCNC]

And the proof...

Well, here are the spectrum graphs for a top with glued braces, vs the top I just cut with the integrated braces....

The GREEN graph is the integrated braced top..
The Light BLUE graph is the top with glued braces..

(Two graphs on bottom are just noise..the mic connected to the analyzer with no volume...)

Here is what I notice:

-As you can see, the top with glued braces seems to be a bit more "BASS-y" and you can clearly see the shift on the graph, but that is EXPECTED! I have not shaved down the integrated braces yet, as they were left larger on purpose..doing so, there should be a drop in pitch, again as expected. Also, the Integrated Braced top (IB for short) still needs to be sanded down....

Again, VERY PROMISING results, and when all done, I would expect the two to be right in line...

So so far, I am not seeing ANY major difference between glued braces vs machined Integrated Braces....

More to come.... :-)

[CyborgCNC]

All,

Just posted a short video on how I machined the top mentioned above...

[ame=http://www.youtube.com/watch?v=WatC-mihuoA]archtopcut.mp4 - YouTube[/ame]

Enjoy...

[CarveOne]

Exemplary work! I'm glad to see that you are taking the time to document the results like this. If your spectrum analyzer has a smoothing/averaging function it should show that the waveforms are indeed a very close match.

CarveOne

[Drassk]

I like that you're taking measurements, but without a baseline it's hard to say what the spectra are actually showing. Half of it is showing that those two have similar responses, but that only shows something if that response is very different from something else. What does the spectrum of a plain 1/4" thick spruce board look like beside those? What about a thin hardwood board or a braced flat top?

Al Carruth has said that all the guitars from the best to the worst sound a whole lot more like guitars than anything else. That makes discerning the differences much harder because the similarities are so strong. Maybe you could run a couple baselines and then chart the differentials of the individual tests VS the average of all the tests?

[CyborgCNC]

yeap...makes sense.

That is next....taking the spectra of the boards...I had actually done that previously, and I will do it again and post. What is quite noticeable, the spectrum of a plain engleman spruce board (I used one which was 1 inch thick), has a considerable higher response...in other words, there is very little lower frequency components, and therefore, little base.

As the top gets carved, there is a noticeable drop in pitch....

I currently do not have any thin boards, so I can't really test those..but will acquire some, and go from there....

[CyborgCNC]

Ok, so here is a comparison between a 1 inch thick engleman spruce block of wood (24 inches long, by 9 inches accross), and the finished top....

The Green graph is of the block of wood, the Light-Blue one is of the finished top plate with the integrated braces, as detailed above...

As you can see, there is a SIGNIFICANT drop in pitch of the sound, and as detailed it is what exactly should happen as one begins to carve the top....as you can see, there is a significant and very apparent shift in frequencies...

More to come....

[rgammage]

Hello

I noticed some mention earlier in these posts regarding tuning by tapping etc. Well I recommend downloading a software called Audacity, you can record a sample of sound and can then do a FFT transform on it to 'see' all the overtones and harmonics.

Richard