Official Luthiers Forum!

I've never arched the bracing for any of the flat top guitars I've made. From reading, it seems that
arching the top strengthens a guitar top just as an arched bridge (think Golden Gate) is stronger than a flat bridge.

But structurally, on the face of it, arching a bridge seems quite unlike what happens when a guitar top is arched
in that on a bridge there is downward force and on a guitar there is an upward pull, seemingly similar to a
bridge only if cars drove on its underside, upside down with reverse gravity.

So my question is, does arching cause stiffness in both directions - from force toward its' concavity as well as its
convexity?

Another important reason to arch a flat top is to decrease the likelihood of cracking from humitidy and temperature changes.

This topic gets brought up a couple times a year.

There are a handfull of custom builders who do not arch their braces and the top is truely flat. Jim Olson, Kevin Ryan, Charlie Hoffman and Bob Taylor with the R. Taylor line to name a few.

If a guitar is brought below an optimal RH level, it will crack, regardless of the arch or not. The strength in arching is indeed for a load bearing on the top of the arch pressing the arch into compression, not the other way around.

Arching does stiffen the top which can cause a change in sound which I think is really the advantage of arching versus leaving the braces flat.

_________________
My Facebook Guitar Page

"There's really no wrong way, as long as the results are what's desired." Charles Fox

"We have to constantly remind ourselves what we're doing....No Luthier is putting a man on the moon!" Harry Fleishman

"Generosity is always different in the eye of the person who didn't receive anything, but who wanted some." Waddy Thomson

An arched flat top guitar will work by adding stiffness and the little extra will allow movement during RH changes. I have not seen a domed top crack unless the top sank. I am in Pa and we do have extreme RH changes . Still it goes to show that there is more than 1 way to build a guitar.

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

I actually just completed my very first true flat top guitar and I am quite pleased with the sound. Same woods and body type as a lot of my guitars but the sound is very punchy and airy if that means anything.