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Cute figures, but you're not cutting out the whole length into the I beam shape, so it's not a full and true I beam. s, toss your figures.... And you didn't run tests on real wood samples. wood, especially small wood pieces, rarely acts like a predictable material that you expect. we see this all too often. Put away the text books and get dirty...

You're not the first one to make little wood I beam braces. It gets tried at least once a year by a newcomer who has just learned the magic of engineered beams. What results is always a brace that is stiffer than necessary, and heavier. every. single. time.

The web part of an I beam, that part between the two flanges is supposed to prevent end to end slipage as bending loads are placed on the beam. If wood were a homogenous material I concede that a wooden I beam would work very nicely. But, I don't think that the center section has its greatest strength oriented in the right direction considering the loads. If you were to put a piece of plywood between two horozontal flanges, similar to the way that manufactured floor joists are made it would work. Otherwise, even though your tooling looks fantastic and it appears functional, I am afraid that I must agree with Grumpy. A triangular piece would give more long term strength for its weight.

Sure I'll toss out the numbers that prove my point. That section sure looks like an I-Beam, who cares if its not a uniform shape all the way across. I assume you taper your UTB height as they approach the guitar sides. As an engineer I would expect you to at least accept the value of the moment of Inertia at that cross section. Dont get defensive because I disproved the comment that "If you triangulate it and make it a touch taller, it'll weigh much less and be just as stiff...."

Johns criticism is much more constructive, but I think he means long term integrity instead of strength. I think the orientation is correct for the web. The web section is essentially like a laminated board if you look at the grain lines assuming its quartered and straight. The concern I have is with the top and bottom flange and its intersection with center web. A round cut would reduce the stress risers at the point, but I'd still have shear stress fatigue concerns.

The numbers dont lie about the stiffness with equal weights. If you want to make the argument that this is more prone to a fatigue failure, I'll buy that. If the only argument is wood dosnt act in a predictable manner, than that would apply to any shape. Then your left with oversizing any shape brace to give it an adequate safety factor to account for this unpredictability. I didnt just learn this stuff. I'm just applying it to a new application. Its not magic. its. just. math.

You asked. If you'd said you knew all the answers, then we wouldn't have bothered....

But once again, because you asked, it's huge, and it's ugly. Huge meaning it's larger and heavier and stiffer than it needs to be. And ugly because there's no elegance to it, no simplicity; just a square member with some pockets routed into it.

And again, run some tests, with wood. The math might not jibe well with your figures...

Never said I knew all the answers. Just spuring conversation/debate. Within that debate I ran some numbers and came up with some answers and some more questions. Isnt that what this forum is all about?

By the way, Lance, I think this Smilie dosnt pass the G rating rule. Kind of looks like the back side of Mr. Smilie. I feel another fart thread coming on.

This discussions does make me wonder how stiff it needs to be. Grumpy says its huge and ugly. I'll take the ugly as a valid opinion, but the huge comment makes me ask how non-huge it needs to be. I get the feeling no one really knows for sure. My Larrivee L and D have 1/2"w x 5/8"t ( I think they measured out that way), the J-200, J-45 and Stew Mac Dr**d plans call for the same. If those are huge as well, I'd really like to know what they need to be. I could run some distructive tests, but that wont tell me what it will do over a 30+ year period. And I'd just have some numbers with nothing to compare it to. What would I be aiming for?

FWIW, I keep an UTB from a 1930 Martin OM on my bench in plain site at all times to remind me not to overcomplicate things. This brace is .255" wide and .497" high, is perfectly flat on the bottom, triangular in cross section, and has ramped ends that thin to about .125 at the rims. It was removed from the top of a guitar that was retopped within the last few years (not due to a structural failure). It takes about 2 minutes to make one.

Sometimes we tend to overthink things and would be better served to learn from those who came before us. Just my .02.

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Jimmy Caldwell
http://www.caldwellguitars.com

Martin continued using the brace at the size that Jimmy states into the 40's, even on dreads. I've not seen one fail, either. Another factor I don't like on your brace that has been mentioned is the small radius of the tapered ends, and how long you made the thin area. That's just asking for it to break, or collapse to some degree at the ends. What you have is the equivalent of designing a long single leaf spring of constant cross section, then adding a short and stiff helper spring. More than likely, the main leaf will eventually break. Instead, what you should have done is added multiple leaves, progressively sorter in length until the stiffness required was reached, correct? Correct.

And the strength needed of the brace this would also depend on how you build your upper bout, the stiffness of the sides, the size and fit of the neck block, etc....

Look at the whole, and engineer the whole.

In order for the top to cave the whole head block has to rotate, which means the whole body deforms a little. Using the ufb to prevent this requires that the fretboard extension act as a lever. I think it's better to put the lever on the back in the form of a Spanish foot and then use a beefier brace in the upper bout of the back to keep it from deforming. I think the Spanish builders that predated Martin were pretty smart.

I believe Mario deals with this by doubling his sides in the upper bout (am I correct?) and Rick uses flying buttresses.

Of course you will need something on the top to reinforce the north end of the soundhole in case the fretboard itself wants to act screwy.

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Randy Muth
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In order for the top to cave the whole head block has to rotate, which means the whole body deforms a little. Using the ufb to prevent this requires that the fretboard extension act as a lever. I think it's better to put the lever on the back in the form of a Spanish foot and then use a beefier brace in the upper bout of the back to keep it from deforming. I think the Spanish builders that predated Martin were pretty smart.

I believe Mario deals with this by doubling his sides in the upper bout (am I correct?) and Rick uses flying buttresses.

Of course you will need something on the top to reinforce the north end of the soundhole in case the fretboard itself wants to act screwy.

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Randy Muth
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Yes, I do double my upper bout ribs, but only since '04. Before that is was traditional construction. It does stiffen the upper bout a LOT. Also allows me to add a soundport at the last minute(or even years later) if the client suddenly decides...

But...

We can have the top sink without the neck block rotation. The bridge is being torqued such that its rotation wants to push the soundhole down into the back, and that is where we see it sink, methinks, and it then just brings the neck block with it, helped by the relentless pull of the strings...

I think the picture may be a bit misleading on the length of the thin section. That is not cut down to final size. That section is at least twice as long as it will be once its cut down.

On that old Martin brace, how far out from the sides does it start to taper?

I do over analyze things, but if we always assume that just because something has been done one way its the best way, well never make and progress. Not to say we shouldnt accept the way things are done if they make sense. Learn from the past, but still question it.

edit: How thick do you made the two piece on the double side? How far twards the waist do you go? Do you use the same material as the sides, or mix it up?

Mario,

Didn't mean to imply that rotation about the bridge also wouldn't doom a top. No doubt the X brace has to be doing its thing, even with Rick's flying buttresses where he eliminates the upper face brace altogether.

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Randy Muth
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I'm estimating here, but it's about 2.25". If I can remember, I'll check it and let you know for sure.

_________________
Jimmy Caldwell
http://www.caldwellguitars.com

Zach, you're not the first to look at everything in order to find a new way to do it/improve it. In fact, I'll wager my career that nothing you can think of, hasn't been tried. What we have today is the result of centuries of progress, tempered by what worked and what didn't.....

My doubles are the same thickness as my sides, and yes, I do mix 'em up at times, usually to reduce mass, but sometimes for the cosmetic effects.

That 2-1/4" figure sounds right, but remember that it's not a small radius, abrupt transition like yours is.

I'm sure I’m not the first and won’t be the last, but its fun learning and trying new things. I'm sure there something that hasn’t been tried yet, not that I’ll ever come up with it. It’s kind of a depressing thought that Everything has been done before.

I think I went 60 mm in from the edge and its about a 2"R. I just kind of drew it in by hand. Is the Matrin a straight taper, scoop or rounded taper?

What really makes me cringe as an engineer is when a builder does a big wide transverse brace then drills a truss rod access hole close to the top of the brace which is then rounded over so there is only a sliver of wood left.

Straight taper.

_________________
Jimmy Caldwell
http://www.caldwellguitars.com

I'll probably just end up using a 7mm brace as shown in the GAL article with Grit.

I thought about not using a hole and using the goofy wrench like Larrivee. I do have three of them from my D, L and P. Dont know if there the same size as whats on the truss rods I have.

Cool and informative. Thanks Zach, and all.

Didn't realize this was from 2008 until halfway through. Great discussion!

James: Are you trying to say it's not 2008...????
Tom

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

Zach I like the looks of the brace, what worries me is the long flat ends especialy if you are using spruce. that is the most important brace as far as keeping the correct geometry of the body to neck joint, over time, with the stress of the constant string pull/pressure ! if the brace moves at all,the neck could begin to rotate towards the body from the headstock ! honestly, that is not a place i would sacrifice any strenghth for looks or style.most guitars that need neck resets begin sinking in there. I would just make the brace full height wider , and the transition to the linings a more abrupt angle.. Jody

Wow, I didn't think you could even resurrect a 2.5 year old thread. I never intended to actually use this on a real guitar. It was just messing around on a practice top. I agree on not skimping in this area.

The math proved my contention on how it was light and stronger in pure bending. Whether or not it is a good idea is something else. But I stand by the math of an i-beam. Its somewhat proven.

As I said in the recent thread this was linked to, it helps to know the basics on how things work in order to best utilize the limited amount of trys we all be in building. It takes a long time to build a guitar to try one little change. The better educated you are on how things work, the better chance you'll used those wisely.

LOL and leave it to me to reply to a 2.5 year old thread ! sheesh ! someone please put me out of my misery! LOL