Official Luthiers Forum!

Hello i was wandering if there is a program or something that you can put the number of strings the scale lenth etc and tell you how much and how tall the braces of your instrument should be to resist the sinking of top....any ideas?

I'm not aware of any such program. There are various ways to set brace size and position. Some use a scientific method that includes stiffness of top, string tension, size of top, top vibration patterns, desired tonal properties, etc. Most just use tried and true bracing patterns, fine tuned by ear.

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Joe Beaver
Maker of Sawdust

xm i see...i am from greece and building greek instruments but its hard to find specs for these instruments..

Much more in play than just strings and scale length. Soundboard stiffness, bridge plate, bridge shape and size, gauge of strings, thinning of plates, ect. ect.

No silver bullet. It's experience either learned or gained from others.

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John Mayes
http://www.mayesluthier.com

+1 for what John says. Too many factors that are simply too difficult to quantify to be able to program something. John Greven has a good paper on his website that may give you some insight.

Good luck,
Chuck

thank you both for your answeres!!

Top deflection is calculable, but for complex geometry the calcs may require finite element analysis to be accurate. Still, you can get a ballpark stiffness using composite beam inertia (parallel axis theorem) + beam deflection equations + some reasonable and perhaps lucky assumptions. Can you post a pic of the bracing pattern?

For sound quality, the right stiffness ballpark is just a starting point; need lots of trial and error, as John said above.

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David Malicky

here you can see the bracing system but the bridge push down not up

Those lateral braces appear tall enough that they will be more or less rigid, meaning that only the lower portion of the top will vibrate very much. So for top deflection calcs, it's mainly the top and that longitudinal brace... pretty straightforward for a ballpark calc. Is there any dome to the top? What does the bridge and string anchor design look like, and where is the bridge placed?

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David Malicky