Official Luthiers Forum!

Hello Everyone,

Just wondering as I am bracing a top, why I am tucking the X and transverse brace into the kerfed lining? Why not just feather them down to fit under the lining? Is it tradition or a structural benefit? Wouldn't the top have just as much contact with the lining, and maybe be a bit more free to move, if the braces were not notched into the lining?

Thanks for the help!

Jeff

Some do and some don't. I do on the x's and nothing else but I've been considering not. How's that for wishy washy

_________________
Tickle your guitar daily, and it'll tickle you back.

Jeff -
I only tuck the upper X and the large traverse brace. I guess if you consider that the fretboard extension is being pushed into the box, above the sound hole, then supporting the upper traverse brace from underneath makes sense, however, the lower Xbraces, tone bars and finger braces are all feathered to nothing just short of the kerfng.

One caveat if not notching the lower braces, you must be aware of your center line, the notch's sorta hold everything square when your gluing, but with out them, the lower bout area tends to slide around when your gluing it down to the rims.

I've thought about drilling two tiny holes to index the lower bout to the end block. They'd have to be tiny and inside the binding purfling line.

LanceK38491.5353009259

_________________
Support the OLF! Bookmark our STEWMAC link Today!
Lance@LuthiersForum.com

Lance beat me to. I tuck the x braces and the upper transvers and notch the rim to act as loctating devices when attaching the top. That way the top just drops right into place with no worry about shifting when clamping

Michael - how do you notch the rim?

_________________
Support the OLF! Bookmark our STEWMAC link Today!
Lance@LuthiersForum.com

Very low tech. I position and clamp the top, double check alignment, reposition and clamp the top, triple check alignment, mark the intersections, down cut with razor saw half depth and file to perfect fit. I am trying to perfect using my laminate cutter but one slip and oops. back to the bender

by the way I used two 3/16 dowls in the neck block to locate the centerline at the upper bout ala Martin Kit style

Something interesting I learned last weekend at the Colorado Luthiers guitar show. Edward Dick(who has built over 300 guitars) was giving a demonstration on carving top braces and as he was doing this, he was explaining that what he has found over the last 30 years of building, is that the upper bout needs to be stiff. I think tucking that upper transverse brace helps to do this. He even went as far as adding a small laminate piece of spruce just about a 1/2" from the kerfing around the upper bout. Then he also uses the fretboard extension piece above his head block that many do here.

He always thought that if you loosened up the upper bout it would help with tone. But after many years of experimenting he found opposite, it should be stiff in the upper bout.

Another tidbit I learned, he says you could lose 10 to 20% of your tone by just having a few fret ends loose! Imagine how much better my guitar will be when I fix those fret ends! Hope this was helpful.
Tracytl50736238491.5728240741

Lance, You don't have to drill all the way through the top to add loacting pins for the tail block. Forstner bits come in small sizes so you could drill a hole .05 inches deep and add a matching dowel to the tail block. I think Julius Borges does this IIRC.

actualy one at the tail block and one at the neck block would get the job done.

Think about the guitar as assembled. If you knock on the top or back over a brace, and the brace is not tucked in, then the blow is trying to peel the brace loose from the plate. Most glues are weak in peel resistance, and hide glue is not very good at handling shock, since it's so brittle. Untucked braces tend to come loose.

Gibson used to feather the brace down to almoast nothing at the end, and allow the brace to sort of crush the liner material to form a little bit of a pocket. The trouble is that sometimes the liner would be harder than the brace, and you'd get a crush across the brace near the end. I can't count how many old Gibbys I've seen with the top shoulder brace peeled loose, or even simply missing.

Feathering the brace completely before it reaches the liner is OK. Fred Diickens used to do that on his backs, claiming that even a little brace plugged into the liner cut down the vibration amplitude. The trick is that the brace has to be low enough at the end so that it's not too much stiffer then the back or top at that point. you're trying to avoid a stress riser, or, if you can't, to be sure that it's supported so that it can't cause trouble.

I tuck in the X brace ends, the shoulder brace, and the two 'A' braces that I run up the sides of the soundhole and into the neck block to keep that from shifting.

BTW, except for looking a little sloppy, I can think of no reason why a gap on either _side_ of the brace as it goes into the pocket would be a problem. It does need to fit against the _bottom_ of the pocket. Top shrinkage can cause the brace ends to 'pop' over time and push out the binding or side. Trimming off the brace so that it does not quite reach the side helps avoid this.

Thanks Everyone for the help. You pointed out some reasons and ideas I had not thought of. Looks like I will keep tucking the x and the transverse.

Jeff

What is the thicknesses of the braces you tuck?

my upper transvers is 3/8 thick, x-braces are 5/16 thick. I scallop each to 3/32 proud at the intersection of the brace /lining/rim

IF (big IF perhaps) you only need/want to tuck the ends of the braces as locating keys, why not just add some very short, brace-like locating keys at the edge of the soundboard and cut key ways for those? In fact you could cut the key ways first and use those to mark the top for where you need to glue on the keys.

Just a thought from a wannabe luthier...

Why ad components that you already have? and as Alan said there is more to the story structuraly

[QUOTE=Alan Carruth]Feathering the brace completely before it reaches the liner is OK. Fred Diickens used to do that on his backs, claiming that even a little brace plugged into the liner cut down the vibration amplitude.[/QUOTE]

In case Fred is right...   

Didn't think this through, so I'm deleting itEricKeller38497.0286458333

NO!

A brace is not a marimba key vibrating independantly in the air. It's part of the structure of the back, which is constrained around the edges. The back vibrates as a whole, even though it has various resonant frequencies that show activity in different places.

Basically, we use braces because they add a fair amount of stiffness with little weight: all of the braces on a steel string top might weigh thirty grams, while the top itself weighs about 150. If you wanted to add as much stiffness without bracing it would probably have to be twice as thick, and would weigh twice as much. That would be one quiet guitar.

Braces add stiffness mostly from their height. A brace 1" tall and 1/4" wide adds a lot more stiffness than a brace 1/4" tall and 1" wide. Cutting down the heigh of a brace always reduces the stiffness in that spot.

The effect on the frequencies of the various vibration modes of the plate are harder to predict. It depends a lot on what's moving where at what frequency. _Generally_ reducing brace height _must_ lower the average frequency of all the modes taken together. It _might_ raise the pitch of a particular mode, but probably not by much.

If it does it will be because the brace is in a spot that is moving a lot, but it isn't bending much. sometimes, for example, removing wood from the X crossing can raise the pitch of one or more resonant modes that are active at that place. However, since _no_ resonant mode moves much around the edge, I would be very surprised if reducing the height at the ennds of the braces raised the pitch of any of them..

Which is not to say that shaving the braces shorter won't make the guitar sound 'brighter' or 'more trebly'. That's a whole other issue that has to do with our subjective impression of sound. 'Sounds like' and 'iis' are often enough different things that one has to be very cautious unless you can get some measurements.

Removing wood from the end of a marimba key reduces the vibrating mass (which is mostly at the ends) without effecting the stiffness (which is mostly in the middle). The guitar plate is another beast altogether.