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Just ran a European Spruce top and a Padauk back through a thickness sander and started wondering if there is a general rule on how the unbraced plates should compare to each other. Now the top is at 2,80mm (0,110") and the back at 2,50mm (0,098") and the back feels quite a lot stiffer. Lengthwise the difference isn't huge but across the grain the back is way stiffer.

So, is there a general rule on how they should compare?

If you find this rule, please let me know asap....

Cheers, Alex

Stevie,

It's my understanding (could be wrong) that the plates themselves need to be thin enough to resonate well, but thick enough not to buckle under tension.

I've never heard anyone make reference to the stiffness of the top and back relative to each other, except when talking about tap tuning them once they are braced. There's a whole thread running right now about tap tuning, and a few folks have said that they tap tune the top and the back to be a certain intervals apart sonically in an attempt to have them play well together.

As far as I know, there's no rule for relative thicknesses of unbraced plates.


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Trevor Gore seems to have a bit of a handle on this subject.
Short summary of his book regarding this - You can use a standard stiffness of top bracing (plus adjustable standard bracing on the back), and obtain target final thickness from tap frequencies of back and top plates.

_________________
The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.