Official Luthiers Forum!

So, I know some of you are aware I'm doing a thunder chief top replacement. It's badly deformed. I was wondering what might be the tonal impact of creating exact replicas of the top Bracing, using sandwiched carbon fiber. Would be as light? Just last a lot longer?

I do use carbon fiber in all of my top bracing. My braces end up the same thickness and height that I used before CF. I suppose the CF causes the mass to be slightly different than just wood, but I would guess the variation would be within the range of spruce from one tree to another.
I don't expect or have I noticed a tonal change.

I think the real value of CF is resisting physical changes caused by moisture variations in the plates.

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Joe Beaver
Maker of Sawdust

Joe, where do you get your carbon from? And what glue do you use for laminating?

Mike,
I get mine from ACP Composites. I use the CL3-37, .022" thickness.

Here:
https://store.acpsales.com/products/236 ... nal-sheets

The CF sheets have doubled in price since my last purchase in 2014. You might want to call them and see if setting up an account will help.

I use their EZ-Lam Epoxy Resin for bonding.

Just a side note: when cutting with power tools be sure to wear eye protection and a dusk mask.

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Joe Beaver
Maker of Sawdust

Thanks Joe. Will do. In this particular case, I can't see just putting it back together using old technology that will most likely fail again. If I can do this, not change tone, preserve the guitar, I'm in with it. I may adopt on my normal builds too.

Mike, I am sold on using CF in braces. I know some may use more CF and less wood in an effort to reduce mass and alter the sounds from the top. But until I buy Trevor's books and spend the time learning what I need to know about sound, tone and resonance, I think I'll just basically go with a wood braced top with CF for added stability.

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Joe Beaver
Maker of Sawdust

Finally got some time to work on the Thunderchief. Top off, old loose Bracing removed, side Bracing added, new back Bracing roughed in, tucked into kerfed lining. Waiting for carbon fiber to arrive to do the top and top Bracing. Totally surprised that sides were laminated mahogany. What?? Is what it is.

does that top look stained? I'm still concerned how to achieve that color.

I'm working on one of these right now. Doing a back crack repair caused in part because the back braces are not tucked into the lining. Also a top crack repair above the sound hole. On your new top I recommend reinforcing this area better due to the short end grain. They didn't do a good job reinforcing this area at the factory in my opinion.

I believe the top is stained. How do you plan to finish it? If I were using lacquer I would mix in some analine dyes in the first sprayed top coat of lacquer (thinned). Probably some vintage amber with a little tobacco brown, maybe some orange and reds. Experiment until I got the color right. Not too dark though since the new wood will naturally darken with age. Another method is to mix up some dye in water or alcohol then wipe on the bare wood, though this method may invite some blotchiness on soft woods. By the look of the finish on this guitar, to get a good match, a wiping varnish may be appropriate and easy to apply. You could also tint the wiping varnish.

I did tuck the back braces. True, they were not originally tucked. I intend to do some tucking on the top too. Gonna make braces identical, but sandwiched with unidirectional carbon fiber. I do not see too many issues on bottom lining. Will add glue where I see gaps. Color matching going to be fun. Gonna order some Tabacco trans tint if it's available and def use wiping varnish.

I do keep wondering if just a little cross bracing behind bridge and in front of bridge might not be helpful in reducing bulge and sink. Very light. Thoughts?

Soundhole reinforcements: I see they epoxied black fiber in hole area before cutting. Maybe some thin hard maple instead?

Couldn't hurt with the extra bracing. It seems under-braced to me for the amount of string tension and surface area of the top. I'd say if the instrument was deformed then it for sure needs some extra/beefier bracing.

The black fiber [patch around the hole is inadequate. It doesn't cover enough area above the hole where the short grain is. I would use a cross grain patch and make sure all of the area of the top above the soundhole up to the lining is covered. I don't think the species of wood matters too much. I used spruce for a patch. I'd say thin maple would work too.

Oh I just noticed they didn't install any reinforcement on the back center glue joint. Unless this is a one piece back, now might be a good time to put a center reinforcement on the back plate glue joint, while you have the top off. They really underbuilt these things!

There is no need for a center strip. Its a "solid" non-joined back. I've got the back and sides properly braced now. The reason for the super light top bracing is sound amplification. I'm wary of doing anything that deviates from that design other than the carbon fiber laminated braces. Yet, It seems to me a few "light" braces in the area of deformation may be warranted.

Well, got the top braces with the carbon fiber laminated stock installed. This stuff is super stiff. Did a good job of reinforcing the sound hole (IMHO).

Nice!
Not surprised you're using CF braces if that's the original style bracing.

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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.

It's not a smart business idea to do something like this. But it is fun if someone will let you do it. And pay for the materials and a bit more for your trouble.