Mandolin Tone bar Height

[Samuel Bieber]

I am building a mandolin using the Siminoff A5 plan. The tone bars are on the top (1/8" wide treble, 3/16 bass as per plan). Any suggestions on final height of the finish carved bars? Plans and book call for tuning with a strobe tuner and that's not going to happen. Top and bars are very nice Engleman (stiff and light). I've built 15 or so guitars but this is my first mandolin.

[Steve Graves]

Final Height = what sounds best in your situation. Using your woods with your measures whatever they are. I truly wish that the final tonality of an instrument could be easy enough to figure on a calculator.
All instruments need to be tuned and retuned and will eventually settle into a voice of their own if you take the time to allow this to happen.

[Michael Lewis]

The stiffness (how high) of the braces, or tone bars, rather depends on how stiff the top is. How carefully did you graduate your top and what are your thicknesses? I don't need to know, as this is a rhetorical question you must ask yourself, but it relates to how you treat your tone bars.

Another aspect to this subject is the arching you have carved into the top. This is a structural consideration as much as a tonal one, so try to make the arching flow from the peak in the center to the recurve around the rim. Avoid any abrupt transitions and avoid too much "dome" effect by semi flattening the arching between the center and the recurve. This is a subtle thing but it helps resist deformation and collapse of the top, where excessive doming works the other way. A stronger top will usually have much smaller tone bars. Tone bars in the Gibson F5s from the 20s are about 1/4" high or thereabouts and taper toward the ends. There are no set measurements other than the widths of the bars, as they are carved after being glued to the top in the "tuning " process, so one mandolin may have rather different bars than the next one.

[Samuel Bieber]

Thank you Michael. I knew there was no easy answer here, I just wanted a general idea of what's required structurally to keep the top from sinking. I'll feel a little better as I thump, flex and carve now.

[Michael Lewis]

When you carve a top too thin and it collapses you will have learned a valuable lesson, and there is a LOT of information to gather from such occurrence. If you look at the original arching (drawings, templates, etc.), and then at the failed arching you will see where the top distorted, then you can visualize the forces involved to make the parts move as they did. Constant string tension is relentless as it acts on the structure, and by observing older instruments you can see how original designs have distorted over the years. by studying these distortions you can see where you need to 'beef up' your design to counteract the forces the strings bring to the structure.

When you carve a top too thick it may hold up very well over the years but it will not sound so well. The art is to find the middle ground where the instrument sounds great and holds it's shape for a very long time.