Official Luthiers Forum!

What is the major difference from having a tight radius such as 14' or 16' from having a larger radius like 20'? should the radius be completely different from a small bodied guitar Vs. a jumbo? Has any one used the same radius on the top and the back such as 20' or 22'?
Let's hear everyone's opinion on the matter.

A tight radius would build a stiffer top from an engineering stand point. A tighter radius will also allow for some extra wood movement due to humidity drops, but we're talking very little here, but it's there.
I've always built with a 25' top and 15' back so I can only partially answer your question.
You can get away with anything you want however, I'm sure of that.

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Jim Watts
http://jameswattsguitars.com

I am about to build a flamenco that will have a 30' top and a 25' back, so they are really nearly the same. Some use the radius to adjust their neck angle. Too much top radius will require a greater neck angle and that you raise your bridge which may result in less energy being deployed to the top.

I ain't the expert though.....Al Carruth, now he's the guy with the answers!

Shane

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Canada

So why is the back always a tighter radius? Would you be safe to use a 20' or 22' radius on both the top and the back and keep it uniform?

The tighter radius on the back is typically to add strength to that part of the guitar as it is the area that typically takes all of the abuse. Also, those hardwoods are heavier so by thinning them more you decrease the weight of the guitar (typically a good thing, makes it more ALIVE) so the increased 'dome' again adds to the strength. As to your question, you could absolutely use your proposed radii on both the top and the back, taking into account what has been offered here as to why the radii are what they are.

Good Luck and let us know how it works out!

Shane

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Canada

I have been using 15' on the Backs and 24' on the tops but I am thinking of trying a 28' or 30' on the top especially for my 12 fret models.