000 12 fret bracing question

[hat]

I'm just getting started on a 000-12 fret build. It will be the elongated body style, and I'm concerned about having enough bracing in the space between the UTB/soundhole area, and the neck block. With the longer body, there's a lot of acreage up there, and it sure looks like an implosion waiting to happen w/o some good bracing. I'm thinking of using something like the Martin 'A' brace pattern rather than the normal Popsicle brace. Or, perhaps just a couple of good stout braces between the neck block and UTB.
What's the normal on this body style? Any recommendations?

[redir]

I like the A-Brace style myself. It's a great idea. You could also add two UTB's. I also arch that area as well for strength and neck angle geometry.

[Alan Carruth]

I use an extended 'chin' on the neck block, with 'A' braces that plug into it and run through the arched UTB, inletting into the upper arms of the 'X' braces. I also have been using a sound hole doubler for several years. I've had a few guitars get dropped or knocked down by customers so that they hit hard on the back of the neck, and so far no issues with the top splitting on either side of the fingerboard and the neck shifting in. Knock wood (softly!).

[hat]

Originally Posted by Alan Carruth

I use an extended 'chin' on the neck block, with 'A' braces that plug into it and run through the arched UTB, inletting into the upper arms of the 'X' braces. I also have been using a sound hole doubler for several years. I've had a few guitars get dropped or knocked down by customers so that they hit hard on the back of the neck, and so far no issues with the top splitting on either side of the fingerboard and the neck shifting in. Knock wood (softly!).

That sounds like a good explanation of what I was thinking of doing. I hadn't thought about arching the UTB - sounds like that is a good idea also. What are the dimensions of the two A braces you use, if you don't mind my asking? I was thinking something like 3/16 x 5/16 - fairly thin and tall, to help withstand that string tension and torque.

[John Arnold]

What's the normal on this body style?

In the late 1920's, Martin used a 0.25" X 0.62" UTB and a 1/8" X 1" popsicle, and that seems to work OK. In the 1930's, the 000's got a 5/16" wide UTB. I do see top sinkage on prewar Martins, but they are over 70 years old, and guitars in general were not treated as gently as they are today. On the guitars I build, I am not overly concerned with their condition 50 years from now.
I arch the UTB, using about a 60 foot radius. Combined with my unique X-brace arch and a flat rim, that results in little or no drop-off of the fingerboard extension.
IMHO, A-braces are a good idea that I would use....if I was not committed to doing faithful 1930's replicas.

[redir]

Originally Posted by Alan Carruth

I use an extended 'chin' on the neck block, with 'A' braces that plug into it and run through the arched UTB, inletting into the upper arms of the 'X' braces. I also have been using a sound hole doubler for several years. I've had a few guitars get dropped or knocked down by customers so that they hit hard on the back of the neck, and so far no issues with the top splitting on either side of the fingerboard and the neck shifting in. Knock wood (softly!).

I'd love to see a pic of that if it's not too inconvenient or if it's not a trade secret. I think I do it similarly though I do not let it into the x-brace. Are your A-Braces square beams through out? I have always feathered the end of mine. Finally when you say 'chin' do you mean in the classical sense like a foot? One more ... is a sound hole doubler, again, in the classical sense a ring of spruce around the soundhole?

[LouieAtienza]

While I own Somogyi's books, I don't build like him, but I do use the L-shaped neck block where the neck block continues under the fretboard, and that buts up against the UTB, unitizing that upper bout area. I don't necessarily arch the UTB, though I do sometimes taper the rim ever so slightly from the UTB to the neck block on a sanding table, giving me a slight neck tilt. My x-braces have open pockets a la Ryan, and I do have A-braces, that actually go through the pockets of the x-braces. At the soundhole area, I either a) use a patch of the same wood under the soundhole, grain perpendicular to the top, requiring me to edge-band the soundhole, or b) make a hardwood rosette that has a rabbet in the back, which interlocks with a corresponding rabbet on the soundhole, relying on the much denser hardwood for strength, and leaving the hardwood edge show through the soundhole.

[Trevor Gore]

Originally Posted by hat

I hadn't thought about arching the UTB - sounds like that is a good idea also...

Think hard before you change the design arching on the upper transverse brace. If you want the fretboard underside (i.e. the top of the neck) to be co-planar with the upper bout of the guitar (which is usually a good idea as you then don't have to build some sort of kink into the fretboard), it is the curvature of the upper bout which sets the neck angle. A projection of a straight edge over the upper bout, extended over the saddle position should have a specific clearance that gives the right height of the strings off the soundboard at the saddle (typically about 0.5" or 12.5mm) and the right action. That specific clearance depends on a few things but is typically around 2mm. The top of the neck is then made to be co-planar with the upper bout and all is good. If you don't think about this critical piece of design, you will either have a gap to fill under the fretboard end or have to take a wedge of material off. Or worse, you will struggle to get a sensible action with a sensible bridge thickness and saddle protrusion.

[Alan Carruth]

I just use the 25' radius of the rest of the top bracing on the UTB and 'A' braces. Yes, this complicates fitting the fingerboard end to the top. What I do there is set the neck end a little proud of the top edge, such that the neck angle gives the proper height projection at the bridge, and the neck surface projected to the soundhole edge just touches the top. I glue a wedge of the same material as the neck to the underside of the fretboard projection, and fit that to the top. This saves ending up with a fingerboard that thins out too much at the end. To each his own.


I usually make the 'A' braces of the same batch of sticks I'm using for the rest of the top bracing. After the gluing surface of the brace is dressed to the correct curve I trim them down so that I'll end up with a pretty much square section. I don't want them too tall where they go through the UTB, as that might weaken it. If they're something like 1/4"-5/16" square in section that's enough to withstand the compression of the neck without buckling, which is about all they need to do. Note that this is a good place to use less-than-perfectly quartered brace stock.

The UTB, the 'A' braces, and the upper arms of the 'X' outline a pentagonal area around the sound hole. Once I know what size that's going to be I make up a patch that size and shape of a wood similar to the top I'm using. Often I will use a lower grade of wood for this, often choosing skew cut wood by preference. Skew cut offers the highest splitting resistance, which is helpful here, and the lack of cross grain stiffness is hardly an issue. Following the practice of violin makers fitting a patch I run the grain of the doubler something like 2-5 degrees off the grain direction of the top itself. This enhances the splitting resistence while not being enough to introduce stress due to differential shrinkage. The patch will be a bit thinner than the top usually, say .08" where the top might be .105 or so; this is adjusted to suit depending on the top.

I glue the patch on right after inlaying the rosette and bringing the top to thickness, and at the same time as the bridge patch. The hole is then cut through both the top and the patch at the same time. Then the 'A' braces and tone bars, which are lower than the 'X' braces and UTB, are glued on

At this point I take the lower end of the 'A' braces down to the same height as the thickness of the sound hole patch. They are left long enough to extend halfway through the 'X' braces. The extended ends of the 'A' braces are then trimmed off to a wedge shape, and a corresponding wedge cut out of the upper arms of the 'X' to fit. This provides a bit of inlet that is needed on braces that are not trimmed away to zero height on the end, but (hopefully) doesn't remove too much material from the 'X' braces. The UTB receives two rectangular notches so that it will fit over the 'A' braces. With any luck you can get it all to fit together so that the inlets don't show.

When the top is fitted to the rim the upper ends of the 'A' braces are trimmed off so that they will inlet into the neck block. This is the 'L' shaped block that Louis talks about, which I started using quite along time ago. I was never satisfied that I was getting perfect contact between the chin and the UTB, and found from experience that even a tiny gap can allow the neck to shift inward in a case where the back of the neck takes a hard blow. It's easier to inlet the 'A' braces 3/8" or so into the neck block and get that to fit nicely. Not that it's all that 'easy' in some respects. One key is to make those braces so that they converge on the center joint right at the upper edge of the top: at least that gives you a point to aim at.

I actually use the 'chin' as a fingerboard support, with the hope that it will reduce top cracking caused by fingerboard shrinkage. My neck block is wider then the fingerboard, and the sides taper in slightly so that the edge doesn't run along a single grain line and concentrate stress. If you don't buy that line of reasoning you can just use a normal end block, and extend the 'A' braces to inlet into it.

Note that the 'A' braces are doing what the 'popsicle stick' is supposed to do; resist shifting of the neck forward from impact. The popsicle stick relies on the glue area in shear, and is less effective with modern glues that cold creep than it would be with HHG. Even then, hide glue is brittle, and can let go from a shock, so the popsicle stick tends not to be as reliable as you might like. The 'A' brace is under direct compression. If it has been inlet properly at the ends it should not allow any relative motion of the end of the neck. That's the theory, anyway. In practice it seems to work.

[LouieAtienza]

Originally Posted by Alan Carruth

When the top is fitted to the rim the upper ends of the 'A' braces are trimmed off so that they will inlet into the neck block. This is the 'L' shaped block that Louis talks about, which I started using quite along time ago. I was never satisfied that I was getting perfect contact between the chin and the UTB, and found from experience that even a tiny gap can allow the neck to shift inward in a case where the back of the neck takes a hard blow. It's easier to inlet the 'A' braces 3/8" or so into the neck block and get that to fit nicely. Not that it's all that 'easy' in some respects. One key is to make those braces so that they converge on the center joint right at the upper edge of the top: at least that gives you a point to aim at.

I used to mull over that one a bit. What I used to do was double-stick tape a scrap block on the UTB and run a clamp through the sound hole to the end of the body... but this kind of got in the way of gluing the top down to that neck block extension, and I had to pad the sound hole to prevent against any mishap. Now I find it easier to just glue the UTB to the rim assembly first. Then I just make a paper template of the A braces, and transfer it onto the assembly on the body. I think though that with the surface area of the neck block extension and UTB to the soundboard, and the soundboard keeping that unit from translating, even without the A brace it would take a catastrophic blow to cause some shifting...

[Alan Carruth]

It does take quite a blow to do it, but it happens from time to time. I hate the repair when it does.