Tone bar braces

[Randy]

Jhon I'd be interested in your procedure for checking top deflection. How and what your looking for.

[tippie53]

What I do is try and establish how much a top moves using a given weight. Then when I brace it so see that it wont' move and adjust the braces to allow movement at certain points off the top. It isn't so much what I do as it is a relationship pre brace and post brace.
I use a 1937 Martin brace layout and Fish glue to brace my tops and backs. I want to know how much the top moves with a weight I have. That way I know if the top is not stiff enough I can make the braces a bit higher or lower. Then I can adjust my scallop to get the post braced top to move where I need it to.
It is difficult to say exactly what I do other than to say I manipulate the braces to stiffen a top where I need it. once you learn to do this you will have a tool to adjust your top
I use a dial indicator and have a granite inspection plate with the top on a set of parrallels at a given distance . I use the body length of the guitar I am building. Weight is placed at the position of the bridge. I can then measure the drop at the bridge.

https://www.google.com/search?q=chladni ... 80&bih=671

[rienk]

Frankly, I don't understand what the scallops accomplish.
I probably haven't read the right resources yet, which might explain the physics of it, but they don't make sense to me... the distribution of mass doesn't seem to line up with where the strength is needed. At first blush, it seems that you could shave off the "peaks" of the scallops without greatly affecting the strength?

Likewise, taller braces are always strongest, but finding the balance between strong and stiff is the important factor. I build airplanes, and know that Sitka spruce has one of the best strength to weight ratio of almost any wood. Add a lamination, and you've taken it a step further. Use a truss system, and you've reached the pinnacle of strength to weight.

McPherson has some of the prettiest bracing.
Take a look at how Batson has done it.

[tippie53]

Red is even better than sitka but was about wiped out for the war effort. It is coming back. The scallops allow the top to move in areas you want to have more movement and will help bring out bass response. Martin guitars from the 1937 era were considered some of the best ever and used a scallop bracing system.
You are correct in lamination adding stiffness . Now you have to put that information to work. The best thing you can do for yourself is start building and keep a log. Soon you will have a base of information to learn how the bracing will effect tone. You also have to maintain the science and structure and bring the art of sound and appearance. I know you ask where can I find this kind of information , and I can say . you most likely won't , so you have to find sources of information here and there and start .
There are 2 luthier guilds ASIA ( Association of Stringed Instrument Artisan ) and ( Guild of American Luthiers ) Start there , You will also find that there are traditional style builders and I admit I am one ,and then you have contemporary builders , so there is no one answer. It is hard to explain but I think it comes down to what you as a builder like.
Mario Proiux in Canada also does a fine job with blending the 2 styles. All I can say is enjoy the journey.

[johnnparchem]

Frankly, I don't understand what the scallops accomplish.
I probably haven't read the right resources yet, which might explain the physics of it, but they don't make sense to me... the distribution of mass doesn't seem to line up with where the strength is needed. At first blush, it seems that you could shave off the "peaks" of the scallops without greatly affecting the strength?

Likewise, taller braces are always strongest, but finding the balance between strong and stiff is the important factor. I build airplanes, and know that Sitka spruce has one of the best strength to weight ratio of almost any wood. Add a lamination, and you've taken it a step further. Use a truss system, and you've reached the pinnacle of strength to weight.

McPherson has some of the prettiest bracing.
Take a look at how Batson has done it.

I know by experience that shaving off the peaks of the x-braces makes a huge difference. While preforming tap tuning taking just a millimeter off the peak can be heard and felt. I have taken too much off of just the peak of a scalloped brace and have taken a top from being too stiff to too floppy. If you map the stiffness of a scalloped brace the peaks are huge relative to a map of the physical dimensions of the brace do to the cube factor in stiffness for height. The braces are there to provide a stiffness to maintain vibration as well as keeping the instrument from imploding.

At different frequencies there are areas of the top moving and areas of the top not moving. This can be seen in Chladni patterns. You can use this localized information to provide stiffness in areas that do the least harm to the output. . As an engineer I also like to try and understand the physics of the instrument and the engineering is important to provide enough strength to keep the guitar together. It is also important to remember that the human ear and human audio processing is non linear in response to stimuli. What is pleasing to most individuals is not a flat well engineered response. The variations are what provides an instrument its unique voice. There is a bracing style that Kasha, a scientist, developed that provided a way based on measurements of an individual top to provide a set of braces that provided an even\clean response across the frequency range of the instrument and maintained concert quality projection of sound. When properly made the instruments did all that he said they would do. There are not that many Kasha style guitars. I think one of the reasons is their voice is boring.

Given that an instrument is designed to be heard and responded to by humans a lot of instrument design is evolutionary. Ideas that work audibly are copied. Luthier's often experiment from a working design to increase a desired metric, sometimes with success sometimes without.

[rienk]

Given that an instrument is designed to be heard and responded to by humans a lot of instrument design is evolutionary. Ideas that work audibly are copied. Luthier's often experiment from a working design to increase a desired metric, sometimes with success sometimes without.

Yeah, that's the hard part.
As a wannabe engineer (I'm an inventor, who hires people who actually know what they're doing) I am intrigued with finding a good starting point, and seeing what (if anything) I can add from there.
It's great when others share what they are doing, so that there is a good starting point for learning and experimentation. I've always been put off by groups that are so "secretive" that they let newcomers make mistakes that are so easily avoided, pretending that things are much more difficult than they are (at least to start). I love airplanes, but there are so few people learning to fly because of how many arrogant instructors there are. Golfing is another expensive hobby which is impossible to perfect (part of the allure) but for the most part everyone is welcome. Building instruments is obviously not for the faint of heart, but for those willing to try, hopefully there are many people willing to share what they have learned.

The reality is, even if the professionals shared all/most of their secrets, a beginner is not going to be able to build as good a guitar - because this is still an endeavor of craftsmanship. And in my case, I'm not trying to copy any one person's work, but I would like to combine the different ideas that appeal to me. Presumably, most of my initial guitars will not sound great (let alone look good). But that is the joy of the chase. The enjoyment is in the journey, not just in the destination.

I appreciate what you said above.
On one hand, it is discouraging to realize how much there is to learn before I can understand how to make a good guitar. On the other, it is a challenge that I look forward to exploring. But I also don't want to reinvent the wheel or beat my head against the wall.

I forget what book it was in, but beside tone, I will be using a deflection measurement to thin my tops down to (5.3 pounds gives at least a quarter inch deflection across an 18" span).

What I would love to find out is, what kind of deflection should we shoot for once the bracing is mounted?
(this should be the same, regardless of the style of bracing used?).

Thanks again for helping us newbies out!

[tippie53]

My best advice is this, the most popular and what I will call the base line of guitars, often considered the Holy Grail, is the 1937 Martin D28.
Don MacRostie documented one and made a print that is available at Stew Mac. Start there. That gives you an acceptable base line. Now once you have a starting point, you can play with material, glues, brace shape, etc. As an engineer it is fun to look at a shape and see how that can be played with. A great example is an I beam.. take that same material and make it a square and it is terribly weak but in the I formation, it is incredibly strong.
The shape, for example is a key, and most of us have developed over time, patterns for the shapes of the bracing. There is no one answer for all the questions, it is not black and white, but many shades from white to black. I can tell you what won't work; poor joinery, rectangular braces, over built or under built. Start with an accepted print and go from there.
You may build the best and most perfect guitar in the world, but if you can't sell it, you won't be commercially successful. The law of supply and demand will help feed you or help you loose weight. As you can see by my videos, I am not doing poorly.
Those that truly know me and come here often describe me as a humming bird on crack. I don't sit much.