Official Luthiers Forum!

Birch? It looks like the spruce and tattered finish one would expect to see on an old, well-used guitar.

Looks to me like a guitar with a spruce top that has been played.

I take back asking the builder's name. Todd was right to omit it.

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Howard Klepper
http://www.klepperguitars.com

When all else fails, clean the shop.

Oh, I figured it out,
the trap door is a sound port shut off gate.
Cool!
Do you think the rh had anything to do with the "cave in"?
How does the lower bout look?
Does it have a radius to the top.
I knew this would be a good thread.

I wondered if the wood under the heads of the bolts is compressed, there's not much surface area under there without washers. Is there any evidence of the neck heel trying to pull away from the body? It seems like if there's not a solid connection at the neck heel that it would distribute the load from the neck a lot differently, making the upper bout carry a lot more of the load. Also, how tight are you really going to get those bolts initially with a phillips head through the soundhole?

I know Somogyi uses a massive L-shape block, and seems like he would have a long enough history with his guitars to know if that by itself is likely to cause problems. Likewise, I think if Martin would have suspected that the L shape caused problems they would have changed it by now to reduce warranty issues.

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Jonathan Kendall, Siloam Springs AR

I don't like the look of the UTB hole. It looks too big compared to the brace. Is the hole larger than the usual 1/4" . If so that could be a big part of the problem. I also don't like the thin soundhole braces. And lastly, the upper bout x brace arms could be not stiff enough. They must also be deflecting too much.

I believe the main contributing factor is the lack of built-in arching in the upper bout. That is what distinguishes the traditional Martin design from Gibson and Larson. If the top is totally flat, it takes very little force to cause the sinking, especially considering the compressive loading parallel with the strings. On the other hand, a little bit of arching is all it takes to balance the compressive load and the downward pressure due to neck block rotation. I use a very slight arch on the UTB, probably around a 60 foot radius.
This balance of loading is why violins can survive very high string tension in relation to their overall weight. The downforce at the bridge is counteracted by the compressive loading, which tends to force an arched top upwards.

As others have pointed out, the upper bout bracing in that guitar is rather weak at the ends. I prefer a rounded convex taper (parabolic?), rather than the scoops in that area of the top. And I leave the bracing about 3/16" tall where it enters the kerfing. OTOH, I thin the lower ends of the X-braces to about 0.09" where they enter the kerfing, because the loading on the south end of the bridge is in the opposite direction.
This comes from repairing so many vintage guitars (particularly Gibsons) where the sunken upper bout is due to the failure of thin bracing where it enters the kerfing.

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John

Just a question.... If the idea of the L shaped head block is to help alleviate top distortion and help stave off a neck reset, would it not make more sense to have the tongue against the back rather than the top? Wouldn't that actually help brace the string tension against the more rigid and non-stressed structure of the guitar?
Brian

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Brian

You never know what you are capable of until you actually try.

https://www.howardguitarsdelaware.com/