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How Thick Do You Make Your Top

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all depends on body size and stiffness of the wood. I usually start flexing and feeling things around .125" with Sitka for an SJ or OM. The last 2 I did ended up at .120" and the other top I had went to .110 for an OM. Usually I see people recommend .125" for spruce. When you've done a few you develop a sense for the stiffness and can feel and hear when it's where you want it.

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This is one case where there is actually a fairly scientific way to determine the right thickness before bracing. It is a technique called "quenching the fundamental" that uses tap tuning.

Start with the top fairly thick. Tap and you will hear a clear note of definite pitch, a fundamental with not a lot of harmonics.

Gradually thin the top. Check the tap tone as you go. It will get lower and lower.

Suddenly the clear single note will become a combination of notes that sort of sounds like a low pitched gong. Stop thinning at this point.

I like this technique because it is easy to describe and easy to do. You will arrive a good thickness without even knowing what the number is!

(Then you have to do the bracing. I don't really have a clear-cut system for that. It does seem that tall thin braces work better than low fat ones.)

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There is another theory which says to use a thick top 3 - 3.2mm and use a slimmer bracing design...

The theory wants that a thin top vibrates much less with bigger bracing then it would if it would be thicker with slimmer bracing...

I have personaly done this in the past with great results on my first 6 acoustic guitars but again wood is wood which could result in many different opposite experiences...

The best is to first build the traditional way, use references which are already written down, then start experimenting...

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  • 2 weeks later...

I started using the technique of holding the top with both hands and wobbling it like a sheet of metal. I was told that once the sound gets louder and more defined than the top is the right thickness. I just did this on a sitka spruce top and it seems a little thinner than i would have liked. I know that growth rings play a part in why different tops of the same species require more or less wood to vibrate the same.

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