Official Luthiers Forum!

After reading Jfurry's thread in Doc-u-build on building his Macassar ebony 12 string with double cross bracing, I have been thinking about the correct positioning of the guitar top on the radius dish. Where is the peak of curvature positioned? Also if, for example, when using a 15 foot radius dish, because the braces are off centre, they wouldn't be shaped exactly to the 15 foot radius or would they?

I ask this question because on other threads I have seen the underside of the main cross braces being sanded across the centre of the radius dish when they should actually (I think) be positioned off centre unless their intersection is at the peak.

Or am I thinking too deeply?

Depends on whether you want the braces perpendicular to the tangent of the curve, or parallel to each other.
As it's a domed structure, I would assume sanding in the middle of the dish would be making the structure at it's strongest/stiffest (I know, assume nothing) but don't think it makes a whole hill of beans either way.
Personally I think you're over thinking it, although I tend to angle my go-bars a little to prevent them tipping over the braces!

_________________
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.

Yea... You are over thinking it.

Think about this:

If you extend the curve of your radius dish what do you end up with?

Answer: A complete sphere.

So no matter where you measure it, you will have the same radius

Cheers,
Bob

It doesn't matter -- only that it will slightly affect the final height at the headblock and tailblock. The neck angle can change depending on where the "peak" is but the "neck geometry" (relative to the bridge and height off the soundboard) will not change -- those things are dependent on the height of the bridge and the bridge location and not where the top peak is. In other words, it is not an issue to worry about.