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There should be some way to make a test rig from scrap spruce mimicking a top and loading it to failure. That would be very interesting.

I have never seen an X brace fail. For those that have what was the mechanism?

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It's not what you don't know that hurts you, it's what you do know that's wrong.

One ones I've seen it's been brought to me for repair. What caused it , can't say for sure .

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The Shallower the depth of the stream , The Louder the Babble !
The Taking Of Offense Is the Life Course Of The Stupid One !
Wanna Leave a Better Planet for our Kids? How about Working on BETTER KIDS for our Planet !
Forgiveness is the ability to accept an apology that you will probably NEVER GET
The truth will set you free , But FIRST, it will probably Piss you Off !
Creativity is allowing yourself to make Mistakes, Art is knowing which ones to Keep !
The Saddest thing anyone can do , is push a Loyal Person to the point that they Dont Care Anymore
Never met a STRONG person who had an EASY past !
http://wiksnwudwerks.blogspot.com/
http://www.facebook.com/groups/GatewayA ... rAssembly/

Put me down as not a fan of the glue rag.

I've seen a fair amount that look like this:

It appears that crack is approximately where the base of the square notch is .

_________________
The Shallower the depth of the stream , The Louder the Babble !
The Taking Of Offense Is the Life Course Of The Stupid One !
Wanna Leave a Better Planet for our Kids? How about Working on BETTER KIDS for our Planet !
Forgiveness is the ability to accept an apology that you will probably NEVER GET
The truth will set you free , But FIRST, it will probably Piss you Off !
Creativity is allowing yourself to make Mistakes, Art is knowing which ones to Keep !
The Saddest thing anyone can do , is push a Loyal Person to the point that they Dont Care Anymore
Never met a STRONG person who had an EASY past !
http://wiksnwudwerks.blogspot.com/
http://www.facebook.com/groups/GatewayA ... rAssembly/

Is it really so bad anyhow if you get a crack at the x brace? (as long as it is not from normal service)
It is easily glued up.
Everything will break anyhow if it is hit hard enough, I don't really see failures here unless there has been some impact.
Sometimes it is better to have an easily repaired break than have the forces transferred further into the structure.

Has anyone ever seen this kind of crack on an X brace with a wood cap? I don't think I could even do it intentionally without causing a lot of damage elsewhere at the same time. But without the cap, any pressure on the X intersection is focused right onto that grain line, making it very easy to break.

Not at all . And I will continue to build with that style. However without experimentation we can't grow .

_________________
The Shallower the depth of the stream , The Louder the Babble !
The Taking Of Offense Is the Life Course Of The Stupid One !
Wanna Leave a Better Planet for our Kids? How about Working on BETTER KIDS for our Planet !
Forgiveness is the ability to accept an apology that you will probably NEVER GET
The truth will set you free , But FIRST, it will probably Piss you Off !
Creativity is allowing yourself to make Mistakes, Art is knowing which ones to Keep !
The Saddest thing anyone can do , is push a Loyal Person to the point that they Dont Care Anymore
Never met a STRONG person who had an EASY past !
http://wiksnwudwerks.blogspot.com/
http://www.facebook.com/groups/GatewayA ... rAssembly/

yes I see more caps fail then cloth
like I said do an experiment. The cloth will give a little and in actuality. The few caps that I have seen fail may have failed for cross grain movement or that the ends were not shaped to meet the brace but rather left square on the ends , thus adding a stress riser.

I don't think the method you use is as important that you do use something to make the joint contiguous. When you notch that brace there will be a sharp corner so the joint should allow for glue. Not so tight that it springs the joint but a soft rub is fine so the glue can fill the joint and make it solid.

this doesn't mean every cap fails or no cloth will. I have seen more cracked braces than failed caps.

_________________
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

I agree.
Something has to give, and an x brace crack is usually an easy fix.
The reason I started taking little micro clips when I got my webcam is they tend to be invisible before and after the fix. I haven't seen many x brace cracks that show obvious symptoms.
Rather than just have the fix show as a charge line on a customers bill, I can now show someone there really was a problem (or was/is there?).

I have a hunch, based solely on my experience, that there are a fair amount of these cracks out there that no one knows about.
I had been looking inside guitars with a mirror for years, including the one in the clip, and not finding many. For some reason, maybe the different angle or lighting, I found quite a few right after I started using the camera from the tail block side and really looking for them. I find many that are small and utterly invisible without looking closely while pushing on the top.
It's made me wonder if the cracks can develop without a single "event". It also makes me wonder if it matters how strong the joint is from a structural failure view. On some instruments you could probably scallop the joint ends of the crossing brace down to 1/8" and they might be less likely to crack. But from a sound stand point.............................................

I'd be interested to hear from folks who see a lot of old martins for example. Try putting a close look and a push on the top of the x into your inspection routine. See if you find them more that you expected. Little one's that haven't gone anywhere. I use to only really look if there was a depression in front of the bridge or some other obvious symptom.
Maybe my sample size is too small and my hunch is just wrong.

Maybe scalloped ends and a velcro cap! After someone sits on the case, just reach inside and cinch the strap tight again!

????

You have seen cracked braces starting at the intersection with intact caps? Seems like if the brace is cracked, the "cap" has failed almost by definition.

That's what I think the glue rag gets you. It allows the motion but doesn't look like it failed.
In addition, the rag can complicate the repair. Even when it's loose, it makes it harder to flex the brace and get glue in. I'd rather glue a new wood cap on than try and re-soak and stick the rag through the sound hole. and if the original rag glue wasn't hide .....................

The sharp corner is the crux of this experiment .......

_________________
The Shallower the depth of the stream , The Louder the Babble !
The Taking Of Offense Is the Life Course Of The Stupid One !
Wanna Leave a Better Planet for our Kids? How about Working on BETTER KIDS for our Planet !
Forgiveness is the ability to accept an apology that you will probably NEVER GET
The truth will set you free , But FIRST, it will probably Piss you Off !
Creativity is allowing yourself to make Mistakes, Art is knowing which ones to Keep !
The Saddest thing anyone can do , is push a Loyal Person to the point that they Dont Care Anymore
Never met a STRONG person who had an EASY past !
http://wiksnwudwerks.blogspot.com/
http://www.facebook.com/groups/GatewayA ... rAssembly/

David, these cracks in the X brace that have no symptoms other than seeing them when you push on the top, does the tone change when repaired? I would expect that a brace with a crack is several times less stiff but just as heavy as before (the rest of the brace hanging there but not contributing tho the stiffness) and would have a big impact on the tone (for better or worse). If pushing on the top makes it open enough to be visible then clearly the bridge rotation is able to move that area of the top more than it would when it is fixed which may also change the geometry in front and behind the bridge. I'm not saying that either the subtle change in geometry or tone should lead one to find a crack, but asking if the repair is obvious once the problem is discovered.

_________________
Bryan Bear PMoMC

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

Hey David what’s your camera setup? I need to do that.
Thanks
Terry

_________________
It's not what you don't know that hurts you, it's what you do know that's wrong.

What I have seen it the thickness of the cap being .060 and that thin of a cap will flex and allow the sharp corner crack . If the cap is to thin or even to narrow from shaping its not any better or even less effective than the cloth .

_________________
The Shallower the depth of the stream , The Louder the Babble !
The Taking Of Offense Is the Life Course Of The Stupid One !
Wanna Leave a Better Planet for our Kids? How about Working on BETTER KIDS for our Planet !
Forgiveness is the ability to accept an apology that you will probably NEVER GET
The truth will set you free , But FIRST, it will probably Piss you Off !
Creativity is allowing yourself to make Mistakes, Art is knowing which ones to Keep !
The Saddest thing anyone can do , is push a Loyal Person to the point that they Dont Care Anymore
Never met a STRONG person who had an EASY past !
http://wiksnwudwerks.blogspot.com/
http://www.facebook.com/groups/GatewayA ... rAssembly/

I'm all for the experiment but I'm not clear on the endpoints you are measuring or maybe I'm not clear on how you are going to measure them.

As I understand it, you are seeking to eliminate/reduce the stress riser from a notched brace. I see at least two questions you should be asking as well as asking how you will measure and define the results:

1) Is it better structurally? This, in and of itself, has several definitions but I think you are asking is it less prone to the brace splitting. This is a great opportunity to do controlled tests simulating the actual stresses involved on all the different joint types. This would also include a batch of failure tests from impact or other stresses not associated with normal playing.

2) What impact does the new joint have on stability (top geometry under load), stiffness, tone. These are the more interesting questions but much more difficult to define and test. The more common joint types have been show to be mostly strong enough for millions of guitars. This new joint may prove to be slightly better in terms of structure but create other detriments to sound or stability. The joint may be a win tonally but end up being a structural failure in a way we aren't anticipating. Or, hundreds of other scenarios.

This could balloon into experiments involving thousands of guitar bodies and mock ups. I'd tackle one question at a time and start with small experiments with specific measurements in mind.

_________________
Bryan Bear PMoMC

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

Absolutely correct . ( 1 ) guitar at a time lol. Again , as stated before .. Not interested in changing the industry . Just interested in testing a different Idea.

_________________
The Shallower the depth of the stream , The Louder the Babble !
The Taking Of Offense Is the Life Course Of The Stupid One !
Wanna Leave a Better Planet for our Kids? How about Working on BETTER KIDS for our Planet !
Forgiveness is the ability to accept an apology that you will probably NEVER GET
The truth will set you free , But FIRST, it will probably Piss you Off !
Creativity is allowing yourself to make Mistakes, Art is knowing which ones to Keep !
The Saddest thing anyone can do , is push a Loyal Person to the point that they Dont Care Anymore
Never met a STRONG person who had an EASY past !
http://wiksnwudwerks.blogspot.com/
http://www.facebook.com/groups/GatewayA ... rAssembly/

I would imagine that besides direct impact, the next most common cause would be placing songbooks on top of the guitar and closing the case.

Sounds like a case of experience talking here ??

_________________
The Shallower the depth of the stream , The Louder the Babble !
The Taking Of Offense Is the Life Course Of The Stupid One !
Wanna Leave a Better Planet for our Kids? How about Working on BETTER KIDS for our Planet !
Forgiveness is the ability to accept an apology that you will probably NEVER GET
The truth will set you free , But FIRST, it will probably Piss you Off !
Creativity is allowing yourself to make Mistakes, Art is knowing which ones to Keep !
The Saddest thing anyone can do , is push a Loyal Person to the point that they Dont Care Anymore
Never met a STRONG person who had an EASY past !
http://wiksnwudwerks.blogspot.com/
http://www.facebook.com/groups/GatewayA ... rAssembly/

Hmm, I actually can't find any numbers for spruce elongation % before break. But I really can't imagine it being enough to allow the mid-brace split to happen. Breaking the cap is a possibility, and maybe it takes less force than I think. In that case, maybe I should switch to a higher strength wood for the cap. Spruce modulus of rupture is 70MPa, Indian rosewood is 114, purpleheart is 152, African ebony is 158, African blackwood is 214.

I think this is an important point. If the joint is tight and well glued, especially the ends of the up facing notch to the sides of the down facing brace, this will help prevent crack propagation from the notch.

If you use preshaped braces as some manufacturers do, and just cover the gaps with a cloth patch...........

I appreciate every ones input and thoughts . However keep in the forefront that this is just an idea for experimentation . I still use and will use the notched braces .

_________________
The Shallower the depth of the stream , The Louder the Babble !
The Taking Of Offense Is the Life Course Of The Stupid One !
Wanna Leave a Better Planet for our Kids? How about Working on BETTER KIDS for our Planet !
Forgiveness is the ability to accept an apology that you will probably NEVER GET
The truth will set you free , But FIRST, it will probably Piss you Off !
Creativity is allowing yourself to make Mistakes, Art is knowing which ones to Keep !
The Saddest thing anyone can do , is push a Loyal Person to the point that they Dont Care Anymore
Never met a STRONG person who had an EASY past !
http://wiksnwudwerks.blogspot.com/
http://www.facebook.com/groups/GatewayA ... rAssembly/

I describe it here a bit.
viewtopic.php?f=10137&t=48811&hilit=camera



I've never fixed just the brace crack. I'ts always in conjunction with new strings, setup, etc. I would be surprised if it was audible. I think its such a rigid spot that even with a crack it still is.
Here's a D-35 that came in for something unrelated. I think sometimes it's necessary to put the vintage style worship aside. Can anyone really argue that cloth is anything but a fig leaf?

If you pull cloth tight and thoroughly saturate it with glue it can be a useful reinforcement in some situations.
But here you have to distort it to such an extent to make it go down the sides, that the fibres on top are hardly likely to be tight.
Cosmetic only IMHO.

when I talking about failure I was talking about the patch of cloth or wood coming free. As far a split braces that is a different ballgame. Most cracks come from stress. If you over stress a top from High or low RH you can expect this to happen. Also over time the bridge rotates and applies more stress. That is what is splitting the braces not the patches themselves.

Yes any sharp corner is a stress riser and that is often where the cracks generate from. That is why I like the cloth patch , you can reinforce the area of the notch a tiny patch or misplaced cloth patch won't make the joint contiguous. Your patch should flow at least as far down as the joint interface.

_________________
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

Does anyone do a carbon fibre\ epoxy patch?