Official Luthiers Forum!

Cutting mortice pockets in the continuous brace is going to weaken it.
This is a care where "better Joinery" will lead to a poorer result.

and cutting away half the height doesn't weaken it ???

Regardless of whether the joint takes you 2 min or 2 hrs to cut you first need to ask yourself the most important question of all. To what ends? What is it that you achieve?

As I see it the joint you show above will still be less reliable than a lap with a cap. I think it is worth remembering that in most cases the joint at the "X" will form the apex of a dome. That dome will necessarily move up and down quite dramatically with changes in relative humidity day in and day out. It would seem to me that the above drawing shows a joint that has ever chance of eventual bond failure because of where it is in the scheme of things, and the amount of endgrain involved.

Whilst it could be argued that the tapered mortise would prevent the joint from falling apart even if the glue joints did fail, it would not prevent the joint from developing the structural integrity of a hinge or the buzzing you would most likely get once things loosened up and good luck with tracing that one down if it happens.

I am all for building better mouse traps, but they must catch more mice to be considered worth of the effort.

Cheers

Kim

Very little if it is capped because you have re-established a continuance.

No, it does not weaken it because the notched side is glued to the soundboard, reestablishing continuity on that face.

I am definitely missing something here.

Notching the brace doesn't cause weakness because the notched side is glued to the soundboard.

OK , I get that.

But why would cutting tapered mortices (as per my primitive sketch above) weaken the continuous brace, when the two abutting braces are glued to the soundboard, similarly establishing continuity ?

Because on the continuous brace. on the face away from the soundboard, you have cut pockets into the sides , reducing the width available to carry the tension forces from bending.

Not to mention you're gluing end grain. And like Kim asked, what's the end result you're after? I thought it was a stronger joint that's easier to make. The other thing is you would have to slot the side of the brace at the correct angle also not a simple 90 and you are relieing on the glue to hold at the butt joints and that's not true with the capped lap. Now if you capped your joint it might be as strong.

Those are some interesting design concepts, but I did mean catenary. Perhaps the most prominent example of a flattened catenary is the gateway arch and they are all based on the hyperbolic cosine function. The force distribution characteristics are what intrigue me, though. The braces would attach to a rather hefty bridgeplate and otherwise have no contact with the top, instead anchoring to ribs in the back. It should then be possible to adjust vibrational modes in all 3 axes while producing a remarkably stable instrument. Perhaps a diagram is in order?

Except for your monopole which you've probably restricted. I'm thinking there might be some ways of getting around that but I'm not entirely sure. Probably would add a lot of mass to make those braces able to vibrate in that axis while still resisting the torque of the bridge.

Have you ever heard of a "low pressure bridge"? It uses an elevated tailpiece and a bridge with a double break angle (string goes from nut elevation to saddle, down and then back up again to the same elevation as the saddle so that there's no torque from the break angle) that allows you to dial in whatever forces you want including "zero" static loads on the bridge with the strings at tension. I think that would be a more interesting way to go about the ultra thin top idea.

_________________
http://www.birkonium.com CNC Products for Luthiers
http://banduramaker.blogspot.com

I wouldn't call my faith in the Martin design blind. It's one thing to have a new idea or think something is better, it's another to build over a million guitars over an 80 year timespan and really shake your idea out. My "faith" in "Martin" is stronger than ever, somebody knew what they were doing. They even anticipated steel strings and designed for them years ahead of time - how impressive is that!

John

hugh.evans wrote:
"The braces would attach to a rather hefty bridgeplate and otherwise have no contact with the top, instead anchoring to ribs in the back."

I think there would be less scope for adjustment of the different modes than on a regular top bracing system. For example, the braces would be angled downward from the top, which would tend to increase stiffness in the 'vertical' plane, shifting the pitch of the monopole upward. I'm also not sure how you're going to handle the static torque of the bridge with only a small contact area between the braces and the top. Finally, I'm not sure how much actual weight saving this would realize. It could be made to work mechanically, I guess, but it's going to be enough different from standard practice acoustically that you might not like the result.

Andy Birko wrote:
"They even anticipated steel strings and designed for them years ahead of time - how impressive is that! "

Evolutionary biologists call that 'pre-adaptation'. It happens a lot, actually: Strad's violins were pre-adapted for the changes that were made in the structure of the violin a couple of generations after his death. The interesting thing is that both the Martin X-brace and Strad's designs were not as successful in their own time as competing designs: Torres' guitars are considered 'better' classicals than Martins, and Amatis and Stainers were more popular than Strads in their day.

Is that really true about Martin? Were they the Ovation of their day, or was a Martin the strat of the roaring 20s?

Um.. not sure Andy want's to be credited with my sa remarks. Sorry Andy.

John

There are a whole bunch of instruments without notched X-braces, and without capped X-braces.... If you don't want to cap one, or want to try out something different .... go right ahead... Don't let our discussions about "Perfection in the Universe" stop you -- just try it out.... No one here is stopping you.... As they say ... The proof of the pudding is in the eating!

On the question about X-brace classicals.... The X-brace system has been around for at least the last 250 years.... It has never caught on in Gut/nylon String guitar circles.... That's gotta tell you something....

Thanks

John

Well somone was buying those old Gut/nylon string Martins with the X brace. And while I admit that many of the owners don't look too happy in those old pictures, I assume it wasn't because of the guitar they were holding.

Didn't Martin use the X on their higher end models in the mid to late 19th century and the fan on the lower models? Somebody must have thought the X was better, or was is just a case of "new coke" vs. "classic coke?" In any case, it was good enough to survive for a long time.

Maybe the X isn't so bad in a Nylon guitar if it's built light enough.

John

Like Mario once said it's like we are trying to build a sports car as opposed to a factory car. So all the little things we do and try are to make what we hope is a better guitar.

Back in the early 19th century most people 'bought local', and very few producers made more instruments than the local market required. Martin's X-bracing caught on pretty well because they wer of good quality and they were available. There were still a lot of ladder braced guitars being made, too. Fan bracing seems to have been more popular in Spain at first, although Panormo and others used it in other places.

In the longer-term competition, when commerce opened up, I think it's pretty clear that fan bracing has beaten out X bracing in gut/nylon string guitars. There are modern makers who champion X, and even ladder, bracing for classical guitars in certain uses, but the majority of users have gravitated toward fan-braced classicals. There's a lot of discussion about why this should be: maybe it's really 'better', and maybe we're all just 'Segovia's sheep'. However it came about, people have been voting with their wallets for a long time, and most go for fan bracing.

But by the second half of the 19th century, (x braces were introduced in the 1840s) Martin guitars were all over the US. And they were making both fan braced and X braced guitars- the higher end ones being X braced. So somebody must have like x braced gut better than fan braced gut at that time period- which was a good chunk of time.

Maybe the introduction of the steel string guitar bifurcated the market in a way that many/most of the people who liked x braced gut liked x braced steel even more and the people that liked nylon more than steel liked ladder nylon more than x nylon.


John

I can think of a couple of reasons right off the bat.

Spruce is a softwood, which means that it is essentially microscopic straws held together by a natural resin. The end grain doesn't glue very well, so a single brace with a notch cut in it offers more support than a brace cut in half with end grain butted up and glued to the other brace, cap or no cap. besides, if you cut down a quarter inch and glue a cap on, you are essentially doing the same thing as notching the x-brace in the first place, IE removing some wood, then reinforcing the wood with another piece of wood. It's the same as notching the 1 brace, and reinforcing it with the other notched brace, but without the advantage of continuous fiber running along the length of the brace for stiffness, which is the real reason for bracing in the first place.

second, the interrupted brace can't be as strong as an uninterrupted brace with only a quarter inch cap holding it together across the break, and butting the cut brace tightly to the other brace doesn't restore stiffness because of the end grain not gluing as well.

Bob Taylor is a gentleman, but I don't see him adopting the split brace-cap idea any time soon, even though he was nice about it.

I'm sure it can be done, but how long will it last?

Interestingly enough, some archtop guitars have a single brace running diagonally across the top, but they also have the added support of the sound post.


Just my thoughts...

_________________
Old growth, shmold growth!

? ? ?

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

I may be missing something here, but it seems to me that all the mention of endgrain glue joint weakness is irrelevant, since the total area of endgrain to long grain glued surface is exactly the same whether you notch the brace or whether you butt it.

It is more a question of mechanical strength, is it not ?

Good point about the surface, but I am sure than in real life if you try to break an X, the traditional variety would hold a whole lot better, likely thanks to the mechanical interlocking, I would guess too.

Anyway, I want to repeat my earlier post: if you want an extra little bit of better bond, switch to animal glue and size the endgrain first. End grain is like a bunch of straws indeed. They soak in a good amount of glue starving the joint. Fill those pipes up, scrape the excess, and glue it. I really can't see how it will not hold up well if all is done correctly, whatever capping is used.

(Also, animal glue will prevent any cold creep under the bellying forces, if such creep ever occurs )

_________________
Build log

Thanks, Alexandru. I will in fact be using hide glue on my first build so will take heed of your advice re sizing.


I am not however convinced at gut level that the notched brace is actually stronger than the method which I outlined above which involved tapered tenons.


It would be an interesting exercise to build both joints and submit them to Matthias Wandel for a destruction test.

Who is Matthias Wandel, I hear you ask ??

The nearest thing we have to a 21st century Leonardo da Vinci, that's who ...


http://woodgears.ca/joint_strength/index.html

The glue will glue up at the top and the bottom of the notch long grain to long grain. As I see it the end grain to side of brace is pretty much just to prevent buzz or squeek and can't be relied on for strength. Come to think of it, on the butt joint how would you clamp that together that wouldn't take some time over a lap joint. Cap it and its the strongest and fastest without a doubt. At least that's how I see it.