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I decided to try something different on the transverse brace. I think I saw someone do something like this with bracing, but it just seems to make sense from an engineering point of view. Cuts out mass and retains almost the same stiffness. Comments...

It's huge and ugly.

If you triangulate it and make it a touch taller, it'll weigh much less and be just as stiff....

People seem to say this a lot, but its not true if you run the numbers. For equal weights, you cant beat an I-Beam. Theres a reason they use these on buildings. John Mayes says this a few times in his tuning video, and it bugs me every time I hear it. Great video though.

Ugly...OK I'll take that as an opinion. Huge...this is the same size as most plans I've seen and the same size as on the original Larrivee L's that this will go on, just without the mass in the middle.

Weigh it. You didn't remove as much mass as simply rounding it over would have.

"huge" because it is square in section.... ugly for the same reason.

That isn't an I beam...

You've done so much work to preserve stiffness while saving a mere gram or two near the center but at the same time you've taken the brace vertically to near nothing several inches from the rim, reducing stiffness while maximizing mass. If you were to graph the stiffness of the soundboard over that brace it might look something like the white line here:



I'd wager the change in stiffness a couple inches from the rim would have a much more dramatic effect on tone (and probably the shape of the top once strung for a while ) than any benefit you might get from shaving a couple grams of weight near the center section of the brace.

Personally I can't see that there is anything 'wrong' with it. In fact, I quite like the look too. I've seen a lot of lump like objects that get called upper transverse braces that don't look too good. The fact that this one might or might not improve on these other lumpy ones tonally is yet to be seen. It's nice to see different takes on old ideas. This is how innovation comes into being, and shooting someone down for having a go isn't good form.

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If God had wanted us to drink beer, he would have given us stomaches.

One more thing to consider is that thinning the middle of the brace like that is going to make it very crack prone along this area. All the sudden changes in stiffness because of the sharp corners will be ‘stress risers’ (unsure of the English term here?), and where this stress can follow a grain line you have a real danger or the wood splitting. The geometry of your brace would make a more sense if it was metal or another material that is more homogeneous than wood.

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Rian Gitar og Mandolin

You got it right!

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Billy Dean Thomas
Covina, CA

"Multi famam, conscientiam, pauci verentur."
(Many fear their reputation, few their conscience)

Not to pile on here but perhaps you want to call it something other then a "Trani" brace.......

Personally I like the look! It looks refined.
I know that Kevin Ko used this very same style, mater of fact, that may be were you seen it, I posted an image of Kevin's top a few months back.

Well done zehley!

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Lance@LuthiersForum.com

If Grumpy or others dont like the looks it, thats fine. Grumpy is just being grumpy. I'm man enough to take criticism. I've seen a lot of fugly looking bridge and headstock designs out there, but thats just my opinion. I'm not of the school of thought that you should only comment on this forum if you like what you see.

I did think about the stress riser issue. I was going to use a rounded bit to get a fillet in there, but didnt have one. These arent going to go in a finished guitar, so I didnt really care. I believe the sharp angle along that line will not have nearly the danger of a crack that if you have a 90 deg angle say on the scoop. Id have to bone up on my statics to determine that one.

As for the scoop. I've seen scoops this far in on transverse braces. This is less of a scoop on my Larrivee's and is what Grit shows in a GAL article. 60mm from the edge.

Calling it Trani, yup that was on purpose. I was waiting for a comment.

Zach...why not just run the numbers and/or do a controlled experiment comparing both structures. Otherwise, the contest of who can pee farther will continue. You have a great opportunity to further the body of knowledge here and have all of us become better informed. Let the chips fall where they may...that's science!

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JJ
Napa, CA
http://www.DonohueGuitars.com

I too like the looks of it but question a few things.

Mass? As I can not easily tell how thick the web is therefore I don't know how much you have actually lighted the brace from its original state.

Are the inside transitions from web to flange radiused? IF they are square transitions then you have pretty significant stress risers in these transition. If you have ever really looked at the engineering of I-beam, H-beam and W-beam you would notice that the transitions from web to flange is radiused with a radius equal to or slightly larger than the thinner of the web or flange. In steel beams the web is always the thinner part of the beam.

I can not agree with you that a H-beam is inherently stiffer than a wedge of the same material and width. and I know the wedge resists flange deflection and long axis twist better than an H-beam of equal mass. Now the H-beam is equal as stiff at the center of web but not at the edges of the flange. That is where the wedge outperformes the H-beam.

Grumpy is just being grumpy

Grumpy is also an engineer, and says it like it is. As others have said, do some work, run some tests. You'll see the results...

Zach I like the way you think bro!

I have to hand it to ya for building practice tops and trying new things as you are. It is a great way to learn and get a feel for something that IMHO one must experience first hand.

Good on ya!!! CLAP, CLAP, CLAP, CLAP (Lance is working on getting me a clapping hands emoticon )

I'm an engineer as well, so to verify my enginerdtuition I ran the numbers as JJ rightfully suggested.

Dims:
Width (b) = 0.50
Height (h) = 0.625
Cutout height (h1) = 0.345
Web thickness (tw) = 0.160

Rectangle
Ix=0.01017
A=0.3125

I-Beam
Ix=0.00942
A=0.1952

Triangle .5x.625
Ix=0.00339
A=0.15625

Triangle to match the area of the I-Beam version. Needs to be about 0.78 high.
Ix=0.00659
A=0.195

Ix is the second moment of inertia, A is area.

As you can see a triangle of the same area is significantly less stiff that an I-Beam. Cutting the channels on both sides cuts out over a third of the weight (in that section) but only looses about 6% of the stiffness. The idea of an I-Beam is to get the mass as far away from the centroid as possible. Even when you round over braces, your taking away the material that will is creating the most stiffness. I thought about doing this on other braces, but it dosnt give you the opportunity to voice a top if you have set dimensions for the I-Beam.

The stress riser thing is still an issue, but if you cut with a fillet in there it will drastically reduce the risk.

Oh, I do have a real job that I should be at, but my tenants waterheater started shooting water all over the place this morning. That sucked. Now that thats all fixed, i think Ill stay home and build a bit.

Hesh-Clap is back.

Wow. New features today. New Smilies and some sweet zoot pics under our names.

I said it would be at direct loading at the center of the beam. But will not be at the edges of flange. because the width of the beam is so narrow in relation to its height I doubt the deflection of the flange is enough to worry much about. My point was that the wedge is stronger at the edges of the flange than a I-beam would be.

If I'm following you correctly, your concern is if you have a point at the outside of the flange there is a risk of the flange breaking off. As this is glued to the top you'll have a distributed load accross the brace. A fillet would help here. If your looking at the torsional stiffness, you may have a point. Thats a different set of equations.

Nice Zach...seems like good info that can be compared and contrasted. Thanks

So while the MOI is about 60% greater for the I-Beam over the Triangle, the Area is also about 25% greater and presumably 25% heavier. Of course, these data always generate more questions like:

...what is the REQUIRED stiffness for this brace?
...if the triangle meets the requirements, then a lighter brace would be better

If it's stiff enough, I'll continue to use the Triangle

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JJ
Napa, CA
http://www.DonohueGuitars.com

Zach,

I'm not an engineer, but I've always been building something.

When I saw your transverse brace I liked it.

Too, I'd seen it before, so it wasn't really anything too new.

We've seen these babies drilled full of holes too, which works.

With 52 dead from tornadoes of Super Tuesday, it kind of brings the importance of engineering to light.

We must build safer houses to live in.

I saw a student telling his story, he was sliding across the floor on his stomach being sucked out of the building. He grabbed a bubble gum machine as he slid past and he lived. Wow.

Kinda puts the old Trani in perspective a bit. I like yours a lot. Matter of fact, what are you going to do with that one?

Don't you just love this little guy, we've needed him a bunch over the years. I bet he gets some major use here on the OLF. Okay, I've had enough!

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http://www.dickeyguitars.com

I didnt do it with any grand sceme to provide X amout of support. I have no real idea what is even required. I was just building some practice tops and started messing around, and thought I'd share. UTB, from what Ive read and seen, dosnt play much into tone. Its just a support beam. Not that this small reduction in weight will be some monumental improvement, but looking at the first top i made it just looked too big and heavy. Its similar size to what I see on most plans. I could have just made it thinner, but whats the fun in that. Plus this is something you can see through the soundhole. Some may think its ugly, but that will always happen. I read a lot about people bracing too heavy and some wanting to reduce as much mass as possible. Other than just show and tell, my only point is that this shape will be stiffer when weights are equal. Nothing more, nothing less.

Hey Zach...in the end, you can do whatever you want on the brace. If you like the look...go for it. I happen to think it looks high tech and non-traditional...not ugly at all. My philosophy is to minimize mass on the tops and your design goes against that design goal. But you're right about the tonal effect...it is probably minimal in this area.

The main point is that you went to the trouble to get objective data and let the chips fall where they may. I thank you for that effort. As far as carrying it forward, it would be interesting to do some destructive testing comparing the two profiles and get an idea what the forces are that are required to break the beam. Guitars historically have been over-braced and I believe that both designs will prevent cave-ins for a century or more...assuming required care and storage.

Thanks again!

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JJ
Napa, CA
http://www.DonohueGuitars.com

Maybe this was a typo, but if reducing mass is your goal, then this is in line with your design goals. You can make it lighter and achieve the same support.

Sorry, you're correct...I neglected to consider the correction you had to make to match the area.

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JJ
Napa, CA
http://www.DonohueGuitars.com