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So, I’ve made a few 1928 body shape L1s. It the guitar in the older pic w Robert Johnson everyone knows. Very round and smallish.
To my understanding this guitar has an actual flat top w no radius, but I’ve never built it wo a radius ha. I’ve always imparted one and gone from there.
So, should I decide to go flat, what things should I consider ? Obviously the top braces aren’t radiused… what else? Dos it complicate the neck angle? Just tossing mud on the wall wo much thought….
Thanks:)
B


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You should probably consider putting a slight radius on the braces so that the top doesn't "invert" when the humidity changes. I have built guitars with a flat rim, but still put a slight radius to the top using the braces. "Flat top" guitars generally pull up some from string tension. How much they will pull up can be hard to judge, and that can complicate setting the proper neck angle.
I think the flatter top can help the guitar have a more open sound with a few more overtones than one that is strongly arched, but I have no proof of that.

Longevity could be a problem, a completely flat plate and braces has little resistance to of cracks with changes in humidity.

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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.

Had a real one in my shop last week for a nut. However it had started life, almost 100 years in it has settled into a beautiful gentle radius.


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I have built several true flat top guitars. I don't know how to describe it but they are just different. In the end the string tension pulls an arch into it anyway so there's that. It's probably more important to get your RH under control when building dead flat. All my true flat tops have an arched UTB because of the downward forces there and also to get the neck angle right as part of my process.

I try to keep R.H. between 42% and 48%. Above the soundhole, X braces and UTB are flat, and below the soundhole I give the braces 1/16" radius. You could probably go an 1/8" if you want to. This gives me the old, traditional sound I'm looking for. When you put a lot of arch in the top, you get what some call the 'new (modern)' guitar sound. Best comparison I can think of is, old Gibson or Martin guitars compared to Taylor's. Taylor makes really good guitars, but that's not what I want my guitars to sound like.

I appreciate all the input


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Where do you live? What is the RH in your locality?

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I think Jim Olson builds with a flat top.

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It's not what you don't know that hurts you, it's what you do know that's wrong.

Interesting thread, hmm....

Pat

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Pat

How about thoughts on flat rims with a 30-60’ radius on the braces? It creates some tension around the edge of the rim (recurve)?


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Brad--

Huss & Dalton sells guitars with two options: either with spherically arched rims or flat rims, both of which have arched braces glued to the tops. They apparently find there to be a tonal difference.

I'm not sure if they still do, but both Jim Olson and Kevin Ryan were building flat tops with no arch in the early 2000's.

Maybe those with the flat rims have a "recurve" on the edge. With the radius the recurve is essentially outside of the rim? I wouldn't have a clue about tone though.

The flat edge might benefit from some edge thicknessing to get movement. The spherical would just be like a very mild dome. Early violins had the low point, a ways in from the edge. They gradually moved outward. It has to be for sound. Sweet sound vs power.

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Why be normal?

Humidity is bad, I’m in ga. It’s HOT and sticky ha. My worship is 45rh constantly, though


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I build some instruments with flat rims and shallow arching of the braces. I don't see any noticeable "recurve" around the edge. As Colin mentioned, putting - some - arching in the plates (with reasonably light braces) can allow the top to flatten out some during periods of low humidity, instead of cracking.
On other instruments - octave mandolins, citterns, bouzoukis - I will use strongly arched plates (cylindrical arching) to give them the sound I want (I don't want them to sound like a guitar).
Ladder braced guitars built with a completely flat top can have it go concave during periods of extreme low humidity. The braces don't shrink in length and the top shrinks in width. One reason I prefer X bracing is the braces are angled, so the "cross grain gluing" effect is less.