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Ah, yes, this looks kinda familiar....

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Wes McMillian
Santo, TX
http://www.wesmcmillian.com

Here is my observation.
OM's usually have tone bars that are more angled across the soundboard ( less parallel to the X brace leg) to keep more cross grain stiffness and at the same time lower the stiffness along the grain, which can help bring out the bass.
Your more parallel design, coupled with your top at .105", plus the scallops in the tone bars might take away some of the trebles that OM's are known for. I think that the cross brace below the bridge plate is a good stiffener for a top of this thickness.

At the recent GAL talk, I noticed that Dana Bourgeois uses thicker (and thus stiffer) tops (.115"-.125" for Adirondak spruce) as a starting point, and then uses less height in the braces than I have been using. I have been making my tops about the same thickness as yours.
That's what I am going to try next-more soundboard, less bracing.

I notice that the top of your A braces seem to but up against the side of the guitar. I think that an important part of the A brace design is to have a solid stop in the head block to lock the whole bracing system. The main force of the strings on the upper bout is trying to fold the guitar right at that point. Al Carruth has a stopped slot for inletting the braces into the head stock and the braces are butted up against the stops.

When I made my A braced guitars, I cut them all the way through like you did. After talking to Al, I decided to install some dowels to put a stop in the slot and to but the A braces up against them. I've attached a crude drawing.

Thanks, Rob. That's certainly something to put in my mental notebook (even better yet, my written notebook for this build). Will be well worth evaluating the finished product with that in mind.

Mike, that is an interesting observation I hadn't thought about. If the idea is to counter neck rotation, then a stop would make perfect sense. I would "think" such a joint would be as effective as flying buttresses such as Rick Turner and company use. One day I'll play with those some, too.

Even without the stop, I would think this joint would be very effective. Sure, it is relying more on the shear strength of the glue lines, but with the upper A-frame being locked in top and bottom and glued on all surfaces, it should be pretty solid. I sure don't see any negatives to adding a stop. I may do that on another build.

Thanks!

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Wes McMillian
Santo, TX
http://www.wesmcmillian.com

Generally Red spruce is much, much stiffer than the average Englemann… Dana likes his Englemann tops at around .135", even .140". You are correct in pointing that Dana's bracing is fairly low.
.105" seems really thin to me for Englemann, but maybe the bridgeplate brace will really stiffen the system and prevent a bulge from appearing behind the bridge. As well maybe this particular top is really stiff.
From my understanding getting more bass out of a top is achieved by lowering cross-grain stiffness.

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Laurent Brondel
West Paris, Maine - USA
http://www.laurentbrondel.com/

My thinking on the A-brace is actually pretty simple:
1) I hate fixing my own guitars, and
2) the top in the upper bout doesn't make all that much sound, but you take what you can get.
Let's look at the problem, and the traditional solutions.

There's a lot of static force on the top in the upper bout. The neck is trying to pivot around the upper edge, so there is a down load on the top above the soundhole. In addition, of course, there is the direct compression load pushing the neck inward. To top it off, as the fingerboard shrinks over time it tends to pull cracks in the top along its edges.

The upper top brace is there to take up the download. It also takes up some of the compression load through shear in the glue line. A popsicle stick brace, because of the much larger glue surface, helps to take up that compression load, and also might help keep the top from cracking as the fingerboard shrinks. The disadvantage of it is that it has to extend out to the sides, stiffening up the areas of the upper bout that might actually be able to vibrate at a high frequency and produce a little sound. Also, the popsicle stick only works well if the glue used has no cold creep. This will be the case with HHG, but not Titebond or any other aliphatic.

There is also the problem of overloads. When a guitar falls over backwards, hitting the neck or the back of the headstock, there is a large shock load added to the normal compression/rotation. This is actually what promted me to add in the A braces: I had to re-top a couple of dropped guitars.

I use a 'chin' extension on the neck block to support the edges of the fingerboard. It extends out past the fingerboard edges, and is cut to a taper, so that it does not run along a single grain line and concentrate the stress. I run it up as close as possible to the upper top brace. In the past I tried to butt it to that brace, as Taylor does with thier neck joint, but it doesn't take much of a gap to allow the neck to shift under an impact load, and a small shift is all it takes.

As has been pointed out, the A braces go through the compression side of the upper cross brace. Leaving that brace tall, and fitting things carefully, seems to leave adequate strength and stiffness there.

I make the A braces about 1/4" square in section, more or less. This should be adequate for the job, and has proven to be so far. I've had a couple of instruments get dropped since I started using these, with damage to the headstock or neck similar to prior A-less instruments that ended up with top cracks, but the ones with A braces didn't fail. They also seem to be more stable in tuning, and move less overall wih humidity changes and the like.

The upper bout may not "make" a lot of sound but in my experience, the stiffness up there, especially related to the ends of the upper X and UTB, has a pretty big effect on bass.

I've been transitioning over to a cantilevered fingerboard with (Rick Turner's?) CF butresses to support the neck load. I tried to implement one new element at a time to get a better idea of the effect of each one. One step along the way was using the CF butresses with a traditional UTB and the fingerboard extension still glued to the top. The only difference was that I was able to taper the ends of the UTB much more drastically since the CF was supporting the bulk of the static load. The increase in bass response was pretty clear.

On a later model, I elevated/cantilevered the FB extenstion and put in some smaller diagonal braces instead of the UTB. I couldn't detect much difference in sound frrom the last version. Hardly an exhaustive study but I'm pretty convinced of a few things....

One is that the area directly above the sound hole can't really do much to produce sound in and of itself (which makes good sense). Second is that the area where the X and UTB start to come together is important. But I suspect it effects the way the top pumps as opposed to actually generating sound from that area.

Another advantage to the cantilevered neck is that you also avoid that issue Al mentioned of the top taking the neck load if the guitar gets dropped.

But back to the A-brace, it would seem that one function that I haven't seen mentioned is that it appears to spread some of it's load all the way to X brace. This makes great structural sense but I assume it also works in reverse. That is, it spreads the load of the X up to the neck block making that area of the X stiffer. Is that good for sound? Do you need to account for that extra stiffness by decreasing the height of the X in that area?

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http://www.chassonguitars.com

I didn't notice much, if any, change in the sound of my guitars when I started using the A-brace. I did notice a change in stability, and certainly noticed the difference when one or two got dropped hard on the headstocks, and _didn't_ need to be repaired.

There is, of course, a difference in the way the top works when you canteliver the fretboard and, and use flying braces to carry the neck load. That's more like an archtop, in some ways. THere are lots of way to make good guitars.

What is canteliver? I've been reading that alot on here lately.

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"After forty-nine years of violin building, I have decided that the search for a varnish is similar to the fox hunt. The fun is in the hunt."
Jack Batts Maker and Repairer of Fine Violins

Elevated fingerboard.

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Laurent Brondel
West Paris, Maine - USA
http://www.laurentbrondel.com/

Thank you Laurent.

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"After forty-nine years of violin building, I have decided that the search for a varnish is similar to the fox hunt. The fun is in the hunt."
Jack Batts Maker and Repairer of Fine Violins

Chuck - Check out McPherson Guitars. Their fingerboard extension does not touch the top of the guitar. It is 'cantilevered! P.S. They sound great, too.

I think that canteliver is something I could never eat even with lots of onions and hot sauce....


(edit: added the liver stuff)

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Steve Walden
Aspiring Builder,
Bartlesville, OK