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Hi Guys-I am building a classical guitar (#5) with a western red cedar top for the first time and wanted some advice on what weight I should use for the deflection test and how much movement I should work towards. I haven't used the deflection test before but I have seen Chris Paulick's YouTube video referencing the Kent Everett system, but of course this was for steel string guitars and a Sitka spruce top. Thanks Paul

Hi Guys-I notice I haven't had any replies to my question. I don't know whether I am using the correct terms, but all I want to achieve is to make sure I don't plane the top too thin and it is structurally sound. The link for the previous post I referred to is above to give you a better understanding. As mentioned in my last post the difference is that I want the deflection range for a western red cedar top for a classically braced guitar-Fleta pattern. Cheers

Don't think people are willing to commit.
Only posts I've ever seen with suggestions for deflection data IIRC was for steel strings.
If you have access to "The Book" (Gore/Gilet) there is a Fleta plan and instructions for plate thicknessing using plate frequency analysis.
Courtnall book Master Guitars has dimensions/thicknesses from an Fleta, don't have it to hand at the moment.

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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 would ask over on the Delcamp forum which is more or less dedicated to classicals.

I know that they tend to leave classical guitar tops relatively stiffer for the given tension than steel strings. The issue is trying to get good clear trebles to balance out the abundant bass available with the nylon strings. Make tops too thin and they end up loose and flabby or nasal and pingy.

Thanks

Hi Paul,
I have deflection targets and data from cedar classicals that I can share with you. I build double tops these days so I have to go way back in my notebooks to get the solid top information. Give me a few days and I will send them to you.
Regards,
Gary

Thanks Colin John and Gary for your advice and help. Very much appreciated. Regards Paul

Fleta uses a big box, so there is a wide expanse of top top cover it! This means that the top has to be stiffer than usual, hence the use of 9 braces. A big box also means lots of bottom end, so the top has to be stiffer yet to have balanced trebles.

Whatever numbers you have available, you will have to cross reference that with your sum experience (I know, 5) and your intuition. And keep notes because if you ever build to this style again you will want to know what you did last time.

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Expectation is the source of all misery; comparison the thief of joy.
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Thanks Douglas for the advice. It's exciting and scary all at the same time building a guitar, but the pluses out way the minuses for sure!! The keeping notes advice is a good reminder, so thanks.

Hi All-from doing some reading on this site and the net, seems that I need to understand Youngs Modulus- is this correct? Also, I am trying to wrap my head around this and is there any good simple, plain English examples anyone can help me with? Cheers Paul

Young's modulus is the measure of how much work it takes to stretch or compress a piece of material of a given size by a given amount. It's related to the bending stiffness because most of the work done in bending (most of the time) goes into stretching and compressing the material near the surfaces. Since work= force times distance, it's also a measure of how much force it takes to bend the thing a given amount; how stiff it is. There are other things at work, usually: there are shear moduli that measure the work it takes to deform the object in such a way as to turn a cube into a paralllelogram, for example. Again, in most cases, these don't account for as much of the work done as the Young's modulus, so we tend to discount them, if not ignore them entirely. They contribute some inaccuracy to the measurement of the Young's modulus, but in most cases it's not enough to be a problem for us.

Hi Gary-any luck with the notes on the deflection tests? Cheers Paul