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As a new builder I started out with a target thickness of .065 on a spruce top classical I am building.
Because of the need for some excess sanding I ended up closer to .055
I would be interested in any opinions on whether I'm in deep trouble because I'm so thin?

I will be interested in hearing the responses. I usually start greater than 2.5 mm (.01") and maybe work down to about 2 mm .08" on the edges, usually thicker. So I am way thicker than your target. I only made two classical guitars , currently working on #3.

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http://www.Harvestmoonguitars.com

Given that the stiffness of a top varies with the square of the thickness, for that particular top you have reduced the stiffness to 72% of what it would have been at 0.065", sounds a lot.

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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.

What you ended up at was 1.4 mm, and that is really thin. Even your target thickness was thin. With the proper bracing, you may be able to get it back to a responsive top, but it will, most likely, take something like lattice to get it stiff enough. As John said, most classical tops fall in the 2.5 mm range around the bridge area and taper to 1.9 - 2.2 around the perimeter of the lower bout, depending on the stiffness of the top. At that thickness, you are going to get some telegraphing of the braces without a doubt. Another option would be a serious bridge plate to stiffen, cross grain. Of course, all of this speculation depends on the piece of wood involved. What kind of Spruce? Might work with Sitka.

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Waddy

Photobucket Build Album Library

Sound Clips of most of my guitars

It's thin, no doubt about it. Oddly enough it wouldn't be that unusual for a Torres and some Santos Hernandez Guitars go quite a bit thinner than 1.4 mm's. It all depends on that particular soundboard and the bracing.

You could use that top, but will probably need to make some modifications to the design. How extensive those would be depends on the top: spruce can vary in stiffness along the grain by quite a lot, and that's the main issue. At a given thickness, some spruce tops will only be half as stiff as others, or even a little less. Knowing the species doesn't help much, since any species varies by quite a lot. Density turns out to be a good predictor, though.

Even with the densest and stiffest spruce I'd want to add in some more fans, to cut down the unsupported span between them and reduce telegraphing. You could even go to a 'lattice' type brace design, which would work even better. Making the string height off the top as low as possible reduces the torque on the bridge, and helps cut down on bellying. Flamenco guitars use thin tops sometimes, and have the strings much lower off the soundboard than Classicals.

that is thin.... where did you get your target thickness from ?

You could also laminate the top at this point as well as changing your bracing. Either way I think you will not end up with the sound response you want form this guitar.

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It's this new idea from recent decades that everyone gets a participation award. - MUX

I'll jump on the bandwagon too, it's really thin. The first question I had was like Johns' above "where did you get your target thickness?"
That said, you might be in good shape for some form of of lattice bracing.

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Jim Watts
http://jameswattsguitars.com

I'm a new builder as well and sure would not want to risk my project in that way when it is so cheap (in comparison to hours spent building) to purchase another top, learn from the experience and get it right.

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Doug

Don't let fear or common sense stop you from trying to build something

I see a lot of posters are writing that piece of wood off, presumably without seeing or handling it. Who knows how it's going to sound at that thickness and beefed up bracing. I certainly don't.

I understand your point - considering the OP is a beginning builder (as he mentioned), would you trust that he/she will get all the variables correct to salvage the thin wood ? He/she may be talented and pull it off and it will be a great guitar. But as mentioned, it would be better to bite the bullet and get a new top at this stage rather than live with doubt built into your instrument that you had spent 100+ hours on.

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It's this new idea from recent decades that everyone gets a participation award. - MUX

I am a complete beginner, so have that in mind when considering my idea. Shouldn't it be more fun to experiment and build the guitar with this top, try to salvage it and in the case of having the worst sounding guitar on the planet, make a new top and install it. It should give you a great leaning curve. Just consider doing it before finishing the guitar, so you can avoid to repairing the finish as well.

Just my 2 cents

String it up before you put on the binding if you want to test it out. That way, if you need to retop it, it's easier and you haven't wasted bindings.

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http://www.CostaGuitars.com
PMoMC

Crikey!! You all make it sound impossible, akin to rocket science. Torres did it, Santos Hernandez did it. It's not that difficult. People have stated 'do it right'. What exactly is that then? Where in the Luthiers bible does it state that a Spruce top has to be 2.5 mm's and if you go any thinner than that it's the end of the world? Just beef up the bracing. If the plan calls for 5 mm high, then go to 8. You will still be thicker than both Torres and Hernandez. The Guitar will survive. Might not survive 100 years, although there's a chance that it will. It might even sound fantastic. Might even sound better that one at 2.5 mm's with thinner bracing.

One part of the equation not being considered is the assembly method: if using a separate neck and body it's a lot easier to do a re-top than on an integral body/neck build.

There's no doubt that thin tops can work, with a variety of bracing styles, but with the top at 1.4mm now, there is not much more to loose in thickness for binding clean-up, finish sanding, ding removal etc. etc.. Given the OP's current experience level I would suggest that he works up a new top if building face down, but go with the present top if building separates. He can learn a lot, might get away with it, but still has a get-out-of-jail card if things don't work out.

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

What's the plantilla size of the top?
If it's FE17 (Torres) size, it definitely can be used (but maybe for a later build).
It really depends a lot on the experience of the builder.
For a starting build, I think it's safer to go for another top.

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Sen CL Goh
http://senguitar.blogspot.com

I once asked Liam Romanillos what his father meant (in his book) by some of the thin Tops of Hernandez. His reply was: 1 mm. Quite astonished I said that the bracing must have been like flooring joists. No, just pretty much standard.
It's scary how thin some of these guys went.
It's a first build. My first build circa 1977 went on the bonfire circa 1978 (it was that bad). Actually it inspired me to do much better. He is almost certainly going to make mistakes. You can't wrap them up in cotton wool. The one thing that you should afford a Guitar maker (any Guitar maker, irrespective of experience) is the right to make mistakes.

Well here's another conversation (actually in my earlier reply): Alter the bracing to suit. Where's the hard part of that, the bit that a beginner will find 'extremely difficult'? What is the bit that will make it an unreasonable Guitar?

Right.

I start fat at 2.8mm target thickness and work down from there to get to what I think is the sound I/m after 2.5 or 2.3 . You could do a double top?? by adding another piece of 1-1.5mm top ??

The problem is beginners have a hard time keeping the top free of problems during construction, so if it starts at 1.4 it might well end up at 1 after removing the battle scars prior to finish. In any case on a small guitar with beefy 7x4 braces or on a larger one with a lattice it might end up sounding quite OK.

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Build log

Just two cents from a newbie (only two completed; both classicals). Vern, I think you've gone too thin for a first build. I would simply set this top aside to be used later, and go for a top that is closer to 0.09 inches. If you've not put in a rosette, you'll be thinning the area around the sound hole even further, and risk as some mentioned above, having to sand more. I understand that others may have taken their tops this thin, but I would recommend something thicker on a first build.

I agree with the others. Your chances of ending up with a successful instrument are far greater if you go with something thicker. You can certainly save this top to experiment with later, though.

I use a fan braced design and go a little thinner than most (usually end up 2.1mm-2.4mm near the bridge and 1.8..-2.0mm near the edges). I don't use beefier fans but do a couple of things like using a fairly massive, solid and unscalloped lower transverse brace (ala Byers) that help me get away with the slightly thinner top.
I'd consider 1.4 to be pretty extreme and, while it is definitely possible to design a guitar that will sound good (albeit probably a bit different than most fan braced instruments) with a top that thin why lower your odds of success on your first go before really having a feel for what you're doing?

Save it for a double top.

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Ken Franklin
clumsy yet persistent
https://www.kenfranklinukulele.com

Someone told me once that the difference between an amateur and a professional is how they cover their mistakes (that's any profession). If it was me on my first build with concerns on the thickness, I would get another top and repurpose the 1.4mm top that you have whether you use lattice bracing, laminated top, or a smaller guitar (or maybe a uke). You will certainly have more experience by then. Good luck in whatever you do.