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I have a cedar top that ended up a little thin at ~.08 - .075 at the edges and was wondering if anyone has tried the John and William Gilbert T-Bracing? I'm running some experiments using some QS pine, and the braces indeed seem very stiff. I'm going to run some additional tests before cutting up some spruce bracing. I'm thinking instead of trying heavier braces, the T-Brace may be the way to go. I'm thinking, however, that if these were the cat's meow, that everyone would be using them.

Or, this top may be a good candidate for a laminated top.


Thoughts?

http://www.schrammguitars.com/tbracing.html

Cedar tops are cheap. Buy a new one. Don't try to fix something that wrong. A top that thin could go on a small bodied guitar with lattice bracing, but only for the experienced builder looking to do that.
Sorry - I know that not what you wanted to hear, but I believe it is the best advice I can give you.

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"An adventure is only an inconvenience rightly considered. An inconvenience is an adventure wrongly considered." G. K. Chesterton.

Steve-
Is this is a top for a classical?
What plan are you following?

Steve Saville has some good advice- if you have any doubts about the top, get another one. Good cedar tops are still quite cheap. You can always use this top for a 'project' or 'experiment' guitar later.

I thought about the T-brace idea a bit after seeing the online references. It seemed to me a lot of work for a slight decrease in weight, compared to a 'traditional-shaped' (gabled) brace. Something in my future, perhaps, but not now. If you need 'heavier' bracing, one of the traditional bracing types should work fine. The braces are not a very big % of the total top weight, anyway.

Cheers
John

yes it's a Hauser style classical.

Never hand plane with a good solid rock tune going in your ipod LOL

I already have a new top (which I'll be more careful with), but wanted to experiment with this one. No use wasting it. The t-braces didn't take me much time to make at all. But again, the more pieces I can glue together by hand, the more fun I have.

I've been using t-bracing for years. Quite honestly, you can achieve nearly identical results in terms of weight reduction by building with a tall, thin triangular profile. The primary advantage of t-bracing is that you can get a nice wide footprint for gluing. The other advantage (at least for me) is that you can be very consistent with your bracing. Essentially, you are making the brace about as light as you can make it by using a t-brace design --- you shape the tone by altering the height of the brace. So with t-bracing, you approach things more from a strategic strength reduction rather than strategic mass and strength reduction. Obviously, by reducing the height of a t-brace you will eliminate some weight but I am talking "big picture" here.

I don't use t-bracing everywhere just for the sounboard bracing below the soundhole. As others have mentioned, to use that top, I think you need to think about either a double-top or some sort of lattice bracing.

Best of luck,
Simon

you wrote at the edges !! so lets say 1"in how thick is it there ? some build tops like speaker cones and these tops are real thin at the edges but gradually thicker towards the bridge. I am working on a ceder top right now that is extremely thin at the edges and thick towards the bridge area.

Lars

I don't think that thickness is much of an issue either.

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My feeling is that with a thin top you don't necessarily want taller braces, but you want more of them. The idea in my mind is to keep the ratio between the top thickness and the unsupported span more or less contstant, so that the top won't dish or belly up between braces. This, of course, is how you get to a 'lattice' top in the extreme.

One of my students, John LaCroix, has worked out a 'fanned lattice' that is pretty nice. Think of having two sets of fans that converge at points that are not on the center line, and overlapping them. He's made some nice sounding guitars that way, and you can cut down the plate thickness and weight without the bracing eating up all of the savings. The other advantage of this is that it concentrates bracing between the bridge and soundhole, where you need it.

In your case, you might try 9, or even 11, fans, rather than the usual 7. Make them commensurately narrower, but just as tall as the usual Torres style. I'm not guaranteeing that this will work, but hey, it's worh a try.

Thanks, Alan-
Greg Byers has also done similar (from the description) lattice patterns - it's definitely 'one to try'.
http://www.byersguitars.com/Workshop/Workshop.html

As Lars has said, the thickness at different points on the top is a useful measure. (Also, deflection tests can be pretty helpful in a situation like this...something I've just started doing.) Hauser used pretty thick tops; other builders like Bouchet had (spruce)tops in the 1.3-1.5-1.7-1.9 mm (.050-.080") range.
Cheers
John

Sounds intriguing. Would it be appropriate to share photos or plans? Since I have the top and will only use it for my personal pleasure/play, I don't mind doing some fun testing. I'm going to combine it with some maple back/sides and even use a maple neck and see how she fairs.

Thanks for all the input. I'm sure I'm not the only one who has rocked himself to a "ahem" mistake.
Steve

Steve -

The T-braces ( as shown in that link) are upside down - at least if you're looking for increased stiffness for a given weight.

The way they are used, the top of the T (or, the flange, if you're a structures guy) is wasted material, because it is at - or very close to - the neutral axis of the beam ( the beam consisting of the plate and the brace working together ) . You would end up with increased weight for the same stiffness, compared to a simple rectangular-section brace of the same height.

The only advantage to that brace configuration is the increased glue area - you would be less likely to have a glue failure. But, spruce glues very well to start with, and I don't think brace glueline failures are common. ( at least, they're not talked about a lot on this forum).



One easy thing you can do to maximize your brace stiffness-to-weight ratio is to leave the braces rectangular in cross-section, rather than taper them to a triangle section. For same height and total brace weight, a rectangular brace will be significantly stiffer than a triangular one ( but, with a bit less glue joint area).


A T-shaped brace ( with the top of the T away from the plate) is even more efficient, but you might end up with problems because of the severely reduced glue bond area. And, it seems like it would be awkward to glue in place.

Phil

If you were to build with a 9 fan Fleta style you could end up with a very nice guitar. Of corse one caveat is that we have no way of knowing if your top is on the stiff side or flexible side.

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Jim Watts
http://jameswattsguitars.com

+1 on Alan's and Phil's posts.

The thinner the top, the less width of top that a given brace can "communicate" with (structurally).

For a beam in bending, the upper and lower surfaces of the beam are "working" the hardest, and contribute the most to stiffness -- remember the cube rule. So for the best stiffness-to-weight ratio (and strength-to-weight), you would want the most material at those upper and lower surfaces, and just enough in the middle to unify it --> the I-beam. For guitars, an I-beam can be achieved by the inverted T-brace, as Phil said, with the flanges formed by the top plate and the horizontal leg of the T-brace. But it's difficult to glue and also to adjust its stiffness / fine-tune, as Alan has said in the archives, IIRC. The double-top design gives equal sized flanges, with a lightweight inside, but also hard to tune.

Kevin Ryan laser-cuts away material in the middle:
http://www.acousticguitarforum.com/foru ... tcount=289
http://www.taylorguitarforum.com/forums ... stcount=77

Or drill it out (in my experience, though, lightening holes take a lot of effort for not much weight savings).
http://www.kinscherff.com/BracingSys.html

Or a router:
http://home.comcast.net/~keiko5/brace2a.jpg

Among the cross-section shapes that are easy to make and commonly used for guitar braces (triangles, parabolas, rectangles...), the tall rectangle gives the most stiffness at the least weight.

I've wondered why parabolas and triangles are often used for guitar braces. Maybe historically, luthiers voiced by shaving where convenient (the edges), which led to parabolas and triangles, and then that technique/design was carried forward? Or maybe glue quality was less consistent, so failures were more common, so more surface area was needed (which triangles and parabolas do supply)? Or maybe high stiffness-to-weight isn't best for tone (but that would open a can of worms, if true)? Or rectangles are aesthetically dull? Or it just doesn't matter that much -- maybe 5 grams difference on the whole top?

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David Malicky

I think the triangle shape brace does everything a T-shape brace does... without needing to add all the extra glue joints.

Otherwise -- I might just try out what Al is suggesting... use a few more fans and call it good.

Thanks

John