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I know I mentioned this in another thread but since I've been putting off bracing due to humidity beyond my control, I've been staring at this top. I'm really afraid I'm going to have problems down the road. It's somewhere around .09, my cheap calipers only measure 2 digits. For all I know it could be closer to .085 and there's final sanding to do so I know it's going to end up at .08 if I'm really careful. Should I go ahead with this?

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Hutch

Get the heck off the couch and go build a guitar!!!!

Depends on the wood, but most likely you'll be better off getting a new one and keeping above .100". With interlocked bracing you can make just about anything survive, but it probably won't sound very good.

I know where you're coming from, but I have a GC soundboard at 0.080", braced accordingly, which sounds pretty dang good.
However, it's not a dread, and I would agree with the assessment, put that top to one side and make another.
Thickness gauge can be home made and accurate, just need an inexpensive dial gauge and some scrap, used one for years.
http://www.homemadetools.net/homemade-thickness-caliper-16

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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.

[/quote]I know where you're coming from, but I have a GC soundboard at 0.80mm[/quote]
Am I reading this right? .8mm is slightly more than .03". Never heard of a sound board that thin.

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"I've been had again"
Tim Benware
Creedmoor, NC

Somogyi's tops can be as thin as .065 at times.

But as mentioned it depends on the wood AND how you brace. I've got a few here that I built as test cases that I kept that are .085 and were very stiff Italian spruce. They sound good to me and have held up well but you can see in the right light some telegraphing of the braces just like I've seen on Somogyi guitars. These are around 12 years old now and no issues but I am also surprised at this.... and there is still time for issues...

Two things are on my mind about your question Sarge. First it's been said here by others that for a first guitar just complete it and get thorough it. There will be lots of stuff you want to do differently on subsequent builds.

Next if it were me and since you likely didn't deflection test or have a database of deflection test results to reference I think that knowing what I know now I would use another top and go thicker. As you noticed final sanding changes things too. Consider doing a top of .115 spruce if you are not doing any testing of the deflection and then final sand as you wish with nothing being critical with these numbers.

In terms of what's the harm a guitar can sound "thin" in my experience with overly thinned tops and bracing that does not properly compensate for the top thickness. Remember that a guitar top will end up being part of a system of the top, braces, design, bridge plate and of course... the load applied to it meaning bridge rotation, string gauges, player attack, music types, etc.

I'd probably replace it thinking that it's too thin.

I know where you're coming from, but I have a GC soundboard at 0.80mm[/quote]
Am I reading this right? .8mm is slightly more than .03". Never heard of a sound board that thin.[/quote]
Miss-type (or brain fart), edited

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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.

I also think you should start with a new top. It's possible that it would be ok, if you know how to adjust other aspects, but since you likely don't, I'd start a new top at .110...

That's confusing. Did you hand type Colin's quote and mistype the number? He said 0.080" not 0.80mm.

A 0.110” top will be about 2.5 times stiffer than a 0.080” top of the same timber. That seems like a fair amount of additional bracewood to make up for a too-thin top. It might be worth sticking close to common top thicknesses as used by the factory until developing sufficient experience to judge when to depart convention.

Our dreadnaught tops in Mr. Arnold’s Adi ended up at about 0.095 at the edges and close to 0.105 at the bridge. SJ tops in stiff redwood and Lutz end up closer to 0.090 at the edge and 0.100-0.105 under the bridge, with top deflection determining where thinning is done. It seems like starting at something closer to 0.110 might be something to consider.

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A constellation only takes shape when one maps the whole.
- Beth Brower

My spruce tops are usually between .095"-.085". My last guitar was made with an LS redwood top and ended up around .080". While I build for fingerstyle and not heavy strumming or flatpicking, I'd recommend .105" for a generic spruce top that isn't tested intended for a dreadnought. This is where Santa Cruz Guitar Co. starts.

That was originally what I mistyped, now edited.

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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.

That does seem really thin but as others have mentioned it depends. This is a good reason why doing deflection testing is an excellent method to determine top thickness.

I threw out .110 as it's my understanding that that's what Martin uses as the initial thickness for dreads.

It will be too thick almost certainly, but as a baseline it's better too thick than too thin. Then test your .110 top, build the guitar, test the guitar, and you'll have something of a meaningful reference. Repeat and each round becomes more meaningful...

As mentioned that is a little thin as a starting dimension, and you may want to use another top. That top will be fine for a smaller or curvier guitar, so save it for another day.

My dress are around 118-120. 90’s at the edges. Just a number in a multifactorial system though.

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

I have seen Martins as low as .090 most seem to be above that Modern martins are thicker .
With yours at .085? I would suggest using 5/16 braces a 1 3/4 plate .105 thick. Light scallop on the X and you should be ok
The thinest martin top I saw was .065 .

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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 don't even have my guitar strung up yet, it isn't banded or even fretted, and I've never done a flat, or mostly flat soundboard with braces for strength and sound, but the post has me thinking. It's a bad habit.

What would be lost with a thin top? I have a very light violin top with a very stiff arch. That COULD be seen as a thin guitar belly with strong bracing. Strong bracing doesn't necessarily mean HEAVY bracing does it? To me, guitar bracing looks like finite element analysis. find places that need bracing, and make them only as strong as needed.

The violin with the light top has a stiff Birch back, and is very easy to play. I don't play, but it is easy for me to play it. What it seems to lack is depth of sound. It can make all kinds of sound, and it never sounds bad; but it doesn't have the overtones that some others do. You can't get it to growl, and the note higher up on the fingerboard are not as different as the same note on another string. It might be great for a beginner, or even someone in an orchestra who is just one component of the sound. For a solo instrument, or in a quartet, it doesn't seem like it would be a first choice.

Is that what a thin top might give you in a guitar? Or since it works in a more percussive way, and sustain should be somewhere in its vocabulary, would you loose way too much punch and clarity? I have no idea. As usual.

As for the original poster, I was thinking that I'd just go ahead. But then I've always worked with carved instruments, and by the time you get down to final thickness you have a lot of time involved. You also have weight, tap tones, and stiffness and flexibility that you can feel, or even test. With a guitar belly without bracing, you have the cost of the wood, and the time to join it. Big deal. Well, maybe a rosette? I don't know.

If it was a first one, I'd say just do it. You are going to find a lot of things that you would change the next time anyway. Pushing through is hard enough without second guessing everything.

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Why be normal?

Thin tops usually loose "headroom" which is not a good thing for a Dreadnaught type guitar. A thin sounding Dread is not desirable. The top will be fine for a smaller bodied guitar, so why not save it for that. If the top could be replaced as easily as a violin top "pushing through" might be O.K., but replacing a guitar top usually entails major destruction and completely reworking the guitar in most cases.

What I get is a hollow, nasal sort of tone, almost like a wah-wah pedal, or high pass filter with resonant peak if you know what that sounds like. Usually worst on the high E string. I think it's due to excessively powerful overtones drowning out the fundamental. I've tried lattice and fan bracing in the south quadrant of the X, and both sounded more or less the same. I also tried gradually shaving down the total bracing stiffness on one until I'd gone a little too far, and the nasal tone was always present, but eventually the bass got muddy/poofy sounding as well.

Next thin top experiment will be to kill the cross dipole mode as much as I can, to see if that's the source of the trouble. From the few photos of Somogyi's bracing I've seen, he uses super tall finger braces which I suspect are for this purpose. I can still hear the characteristic thin top sound in his guitars, but it's suppressed enough that it doesn't sound bad.

I will start a new top and save this. I guess it would be a good top for a classical. Thanks everyone.

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Hutch

Get the heck off the couch and go build a guitar!!!!

"Next thin top experiment will be to kill the cross dipole mode as much as I can, to see if that's the source of the trouble. From the few photos of Somogyi's bracing I've seen, he uses super tall finger braces which I suspect are for this purpose. I can still hear the characteristic thin top sound in his guitars, but it's suppressed enough that it doesn't sound bad."

Kill de pole mode - isn't that a global warming thing? Does Somogyi build dreadnoughts? (is the Mod- D really a Dreadnought?) I don't see many Bluegrassers playing Somogyi's.
But seriously, if you are building a thin top do you really want to use a dreadnought shape? Some of the old romantic guitars have really thin tops, but they are tiny! I know we are not held to the same constraints as a factory, but still, trading top thickness for complex bracing schemes seems like a bad idea.
I enjoy experiments and like hearing the results. It's kind of like when a person asked me if I "could take a joke", to which I replied "as long as it's not on me"

I've built two with thin tops. Both suffered from a lack of dynamic range which is really annoying for this player. Individual notes are not clean but seem to run together. Just my opinion/experience. One has been retopped and the other is on the bench for a new top - yes, I think they sound that bad. I've no doubt that Somogyi and others can brace/compensate to produce awesome guitars but that's not where I'm trying to go so have no desire to chase that rabbit.

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Steve Smith
"Music is what feelings sound like"

I got out my micrometer and measured again. It's no less than .095" around the outside and around .110" around the soundhole. It feels pretty stiff longetudelly. Of course I don't have a reference. I think now that I can use this. I need to toss those cheap calipers.

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Hutch

Get the heck off the couch and go build a guitar!!!!

Although there is a 'correct' thickness for any top, it's hard to know exactly what that is without some sort of measurement of the stiffness. You can do it by 'feel', or by deflection under a known load, or you can measure the properties of the wood some other way. The salient variable is the Young's modulus of the wood, which determines the stiffness at a given thickness. It tends to track the density of the top pretty closely; if the density is high the Young's modulus also tend to be, but that's not written in stone. In the measurements I've gotten the density predicts the Young's modulus within 10% about 60% of the time.

Some folks who have been tested out with samples of wood of known stiffness are very good at making that determination by feel. However, most people are not nearly as good at it as they think they are. It's better to get a number if you can.

David Hurd, in his 'Left Brain Lutherie', goes into deflection testing at some length. I have not looked at the book for some time, but he may have a way of measuring it that will give you the information you need. Most folks do the measurements before cutting the top to shape.

If those numbers are accurate that top should be fine.