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Is there an sort of optimum height/length for X brace caps to retain stiffness but avoiding "excess"?

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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 use a piece about 1/16 by about 2 inches long .. its really there to stop the open end of the brace from spreading, as the majority of the force in the area is downward, from the forward torque of the bridge. In the series of videos of Ervin S. taken at Healdsburg years ago, he mentions that Judy Threat had taken this patch down to 1/64th and it still was beneficial. The difference on weight going to 1/16 is nothing.

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Tony Karol
www.karol-guitars.com
"let my passion .. fulfill yours"

Mine is about the same as Tony's, and I agree with his points. Even a really thin sliver of spruce can be tremendously strong in this application. I split off a piece of spruce, usually from some brace scrap, for it. I've seen some folks use rosewoods etc, and I have to wonder what the perceived benefit is. If anything, most exotics are more difficult to glue than spruce on spruce.

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Rian Gitar og Mandolin

Arnt, don't you know the species of wood used in the cap effects tone? But I do as you and Tony using a piece of spruce, tone be damned.

Stan, why didn't I think of that ?

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Rian Gitar og Mandolin

Mine starts at about 1/16th by 2in but then gets carved and sanded into the brace profile. I use spruce if for anything just to hide it as best as possible.

As Tony pointed out weight is not much of a factor due to the small size but I think stiffness in the X crossing comes into play,so that should be one of the determining factors. Most times I've used 1/16" material but have some guitars on the bench that I'm going to use 1/32".
Tom

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A person who has never made a mistake has never made anything!!!

As Tony pointed out weight is not much of a factor due to the small size but I think stiffness in the X crossing comes into play,so that should be one of the determining factors. Most times I've used 1/16" material but have some guitars on the bench that I'm going to use 1/32".
Tom

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A person who has never made a mistake has never made anything!!!

I usually cut the top notch about 2/3 of the way down, and then use a cap that's about 2-3mm thick. Leaving the cap off can certainly alter the 'free' plate resonant modes, making them much more asymmetric, even when the joint is tight. That cap does something, alright.

As far as I'm concerned, what counts is more the length of the glue line on either side of the cut, so long as the patch is thick enough that it won't fail in tension. Since the braces are trying to spread that joint open under bridge torque, the glue line between the cap and the brace is in shear, and you need enough length along the line to keep it from peeling loose. I usually use a 2" or so long patch, and taper it out.

I'll note that even a cloth patch helps a lot. I've seen any number of non-patched lap joints that have split at the bottom of the lap, and the repair that works is to glue the split, and then put a cloth patch across the top. Often, with modern production guitars that use CNC pre-shaped braces, you can't use a patch because there's a big gap where the upper brace is rounded off before it's inserted. The cloth patch (linen is really good) bridges that pretty well, and once the brace can't spread the glued split seems to hold pretty well. It won't hold without the patch.

I use the cloth patch. As a repair guy I have seen a few of the wood patches on the bench for repairs. Most of the failed ones had a short patch and didn't bevel the ends or captured capture them in a joint to allow a stress riser that caused a joint failure.
As Alan points out you need a good glue footprint. I like to see the ends tapered off or the patch inletted into the brace to avoid the stress riser.

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

[quote="bluescreek"Most of the failed ones had a short patch and didn't bevel the ends or captured capture them in a joint to allow a stress riser that caused a joint failure.[/quote]

John - I don't follow you here. Can you please clarify? Thanks.

I always use a small strip of Brazilian just for good luck!!

Mikey

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The Biggest Little City, Nevada
www.hammondguitars.com
I love building guitars!

doesn't everyone know that the patch must be old growth br split from a billet that was cut from the south side of the tree and aged and acclimated at least 50.7 years in your shop to a precise emc of 8.013% for at least fifty years and glued in place with hhg made from the hide, hooves and horns of stradivari's great aunt's favorite cow and dissovled in water from shangra la to be even minimally accepatable????

No wonder I failed. I have been using hot hide glue made from unicorn hooves. . .

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Bryan Bear PMoMC

Take care of your feet, and your feet will take care of you.

What about about making the ''upper'' brace 2-3mm thicker and make it go over the ''lower'' one, no notch?

Just like that...

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Francis Richer, Montréal
Les Guitares F&M Guitars

IIRC, that would not serve the primary purpose of the cap, which is to reinforce the "bottom" brace in tension.

Ti-roux asked:
"What about about making the ''upper'' brace 2-3mm thicker and make it go over the ''lower'' one, no notch?"

Because that makes all the 'upper' braces stiffer than the 'lower' ones, and if they all go the same direction, the top ends up with asymmetric stiffness. That's part of what capping the brace works against. If you look at the 'free' plate modes on a top without the brace cap, they will usually be pretty asymmetric, like a top that has a lot of runout. Capping the brace cuts down or eliminates that. Even a tight lap joint is 'loose' acoustically.

That's what I thought... But if someone is looking to break the symmetry...?
Regarding that... What's the advantage of having a symmetrical or assymetrical bracing pattern?
The most commun bracing pattern IS assymetrical, by the tone bars.
I'm personnally thinking to put these straight across the grain on my next steel string.

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Francis Richer, Montréal
Les Guitares F&M Guitars

I did an experiment some years back comparing 'symmetric' and 'asymmetric' braced guitars that were otherwise as 'identical' as I could make them. Most poeple who tried them without knowing which was which had a slight preference for the symmetric top. Many poeple did note that the asymmetric top had a more 'traditional' sound, while the symmetric one was ore 'modern'. Whatever that means. I will say that, when IO was carving braces on asymmetric tops I was always trying to get the 'free' plate modes to be as symmetric as possible; minimizing the asymmetry to the extent it could be done. I think that too much asymmetry can hurt, but I can't prove it.

That's interesting, Alan. When I was watching one of the Bogdanovich CD's, on brace carving, he was particularly careful to make sure that each brace was carved to a different length, to promote the carrying of many notes, and favoring none, or something like that. My guitars are real symmetric. He didn't expound on the subject, though I wish he had!

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Waddy

Photobucket Build Album Library

Sound Clips of most of my guitars

Alan, with one leg of the X so much weaker than the other before the cap is glued on there would be significant asymmetry in the way it vibrated with the whole structure wanting to twist. Or more accurately, wanting to vibrate along the axis more inline with the uncapped leg.

On the historical sound, Trevor discusses this in his book using the J45 slope shouldered dred as an example. That what people tend to perceive as a great sounding X braced dred has particular top frequencies and tapered braces that induced a diagonal dipole, strongly asymmetric. And it leaves a nice scooped mids sound that makes it perfect for vocal accompaniment. Interesting stuff.
Cheers
Dom