Official Luthiers Forum!

For a comparison, take 2 assembled x-braces, (1) standard notch and (1) with the "arch" notch and set them both on 4 blocks each. Start adding weight in increments of --- until one breaks. The arched one will surely break first if built the way you show it. Then build another "arch" notch x-brace with each notch being at the outside of a knothole with the knot removed on each leg of the brace where the grain will swirl around the "arch" and compare that to the standard square notch type of x-brace with the same weights. You could probably use 1 x 2's shaped down and do it on a larger scale for ease of getting the grain like you want it on the "arch" notch.

I don’t think it is as sure as you think that the arched brace will break first in the test you propose. The point Wud is making is that the squared corner of the notch concentrates all the stress right at a grain line along the weakest plane of the wood (which is why we split bracewood to make that weak plane as long as possible inside the brace). The arched notch will spread that force out over a larger area and of end grain. I’m not saying the square notch will break first, just that you can’t assume it won’t.

The problem with designing these tests, and what I was trying to get at in an earlier post is that you have to design a test that simulates the real world forces and seeks to answer a relevant question. In the test you propose, the forces are not similar to the forces the joint will see in use. On a guitar, one side of the joint is completely glued to a spruce top closing the bottom notch. The top notch can be closed in several ways too. The force on this joint is pulling across the top and rotating a bridge down behind the joint and pulling the fretboard extension down in front of the sound hole. The boundaries of the top are not free and have a waist close to part of the joint further complicating the stiffness of the plate. All of that would have to be designed into the experiment.

Then there is the matter of what question are you answering. This test would show which joint would break first if you sat on the guitar top. IMHO, that is not a relevant test. Any joint would fail at some point under a load that the guitar is not intended to handle. Do we care which one would fail first. I suppose so, if one were so weak that somewhat rough handling would lead to failure but I suspect either would hold up to reasonable bumps.

_________________
Bryan Bear PMoMC

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

[/quote]The point Wud is making is that the squared corner of the notch concentrates all the stress right at a grain line along the weakest plane of the wood (which is why we split bracewood to make that weak plane as long as possible inside the brace). The arched notch will spread that force out over a larger area and of end grain. I’m not saying the square notch will break first, just that you can’t assume it won’t.[/quote]


Exactly Bryan. The lower arch is connected all the way across and will be capped across the upper . It is an assumption to state either will fail first . Too many variables involved. Each case could be different, however in time the % would start to tell the story.

_________________
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/

Jim - If you really want to try this out for the sake of trying it - go ahead. You can't bake a cake without breaking some eggs. And often you learn a lot of interesting things by just trying it out to see what happens..

That said. I am going to put on my Grumpy Uncle John hat.....

This seems to be a solution in search of a problem....

Millions of X-braced guitars are made every year. X-braced guitars have been made for the better part of 150 years. Failure of the main X-joint is not a common failure by any means - even when the X is not capped at all... I have handled a bunch of guitars - including a bunch of broken ones... So far I have run across zero with a broken X at the joint.... I won't say it doesn't happen because I have seen pictures.... But I don't think anybody has it on their "common repairs" list....

So... If you are looking for a bona-fide structural deficiency with the current design - this isn't one.

If you just want to try it out - have at it.

Jeez John, now you've got me feeling self conscious about my clientele. Bunch a ruffians I guess.
I would say I'm a very low volume one man shop.
you've seen none?


Crappy laminated guitar and a D-28

What about butted X braces (no notch)?
Anyone see failures there? By separation from the soundboard?

That D-28 took a substantial top hit... Did somebody sit on it? Kids practicing kung fu? Its not often you see crossgrain top splits at the finger braces.

All I can say is that guitars aren't furniture - guitars are fragile by nature. If your clients need one for a bat - there are plastic ukulele's out there...

Is this a thing?

Gibson has already tried it.

Yes I know Gibson has used it, wondering what results have been seen by repairers.

Braces are .750 high and .3125 thick with the Cap it is .875 at X

_________________
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/

Glad I used laminated bracing all these years...