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Working the upper "X"
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=22040		 Page 1 of 1
Author:  Wes McMillian [ Mon Apr 20, 2009 11:35 am ]
Post subject:  Working the upper "X"
Today my guitar building education took a major turn. As I was carving the braces on my latest dread, I suddenly determined to take special notice of the upper legs of the X-brace. Up until now, I have focused more on the lower bout and would just shape the upper legs according to some pre-prescribed formula (basically according to the S/M plans). Now, we know and preach that any bracing system is just that - a system. And we have heard several (Mario being one) who would preach and preach on the contribution of the upper bout. But....WOW! As I worked to reduce mass on the upper legs of the X, triangulating them and tapering the ends thinner than I normally go, I was amazed. As in, my jaw literally dropped when I tapped along the upper legs and the top as a whole. It was really THAT dramatic. I don't recall a single discovery in recent memory that has had me this excited. I know this sounds over-the-top, but I sincerely don't think I'll ever be the same again.

I already can't WAIT to get strings on this one!
Author:  Chris aka Sniggly [ Mon Apr 20, 2009 12:38 pm ]
Post subject:  Re: Working the upper "X"
....and I'll chime in and say I think you are right.

I am on my 3rd guitar. When I was carving the braces on my first I had no idea what I was doing. I didn't even have a plan that specified what they were supposed to look like. My plan told me what their rough dimensions were supposed to be but that was it. Not knowing any better I scalloped the X legs forward of the sound hole.

To date...my first is the best sounding guitar I've made. It's an OM that will give some dread's a run for their money. Disclosure: The top of the first guitar is significantly warped just below the sound hole so I am now more careful. So careful in fact that my second guitar sounded like a Jay Turser wanna be. Way over braced.

I'm with you - sound can be found up there.
Author:  bluescreek [ Mon Apr 20, 2009 1:24 pm ]
Post subject:  Re: Working the upper "X"
I will add just one thing. The top is under 3 major stresses , Compressive , rotational and tension. Be careful as the upper part is carrying the major load of stress from compression and fighting the neck block rotation. If you under brace this area you will know it pretty quickly as the neck will want to roll .
I agree that the upper bout is a great contributor of tone but this is also the major load carrier. Keep a log of what you do so that you can balance it. Once you dial in what you can and cannot do you can work the area to the best advantage.
john hall
blues creek guitars.
Author:  Wes McMillian [ Mon Apr 20, 2009 1:45 pm ]
Post subject:  Re: Working the upper "X"
I hear ya, John. Part of my "system" also includes "A-frame" upper bout bracing mortised through the UTB and solidly into the neck block to help counter this rotation.
Author:  Jody [ Tue Apr 21, 2009 5:19 pm ]
Post subject:  Re: Working the upper "X"
so Wes, just in the spirit of debate, it seems to me your system still puts most of the torque on the transverse brace. Jody
Author:  Wes McMillian [ Tue Apr 21, 2009 7:57 pm ]
Post subject:  Re: Working the upper "X"
I'll try and get a picture before I close the box tonight. But, actually, no. The rotational load on the neck block is transferred, in part, all the wayback to the upper legs of the X. The load, at least in my way of thinking, is shared by the A-frame struts themselves, the UTB it is mortised through and glued to, and the shear load on the glue line of the struts themselves.

Whether it is or is not - hey, it makes me feel better.
Author:  Wes McMillian [ Tue Apr 21, 2009 8:29 pm ]
Post subject:  Re: Working the upper "X"
Here's some pics off the last OM I finished. I've already killed too much time on here, I may not get the box closed tonight after all. I'm off to go see,though!

You can see the upper leg of the X were pretty massive here. I imagine that is one reason I'm seeing such a dramatic response, is because I've been overbuilding in the upper bout. All of the movement would have been behind the X, reducing the overall monopole "pumping" action of the top. I will say this was a heck of a good sounding guitar, though. It'd be interesting to see what some brace shaving would do when I get it back.

Image

And showing the neck block mortise. The box is really not distored like the picture suggests, it's just a figment of the camera's imagination, although it does have about a 3/8" wedge to the body:

Image
Author:  Jody [ Tue Apr 21, 2009 9:48 pm ]
Post subject:  Re: Working the upper "X"
now i see what you are doing . nice job there, Jody
Author:  Frank Cousins [ Wed Apr 22, 2009 1:43 am ]
Post subject:  Re: Working the upper "X"
I am a novice, but from many bracing patterns I have seen here, there does seem to be a reluctance to scallop the upper sections of the X brace... the stress and strain here is very high for sure, but is there a tendency to over worry about this?

I thought about this and after discussing this with a very experienced classical builder, decided to try a bit of a blend... using a 'slipper' heal block, that extended some 50 mm under the top/fingerboard, combined with a soundhole reinforcement ring, I took the plunge and scollopped the upper areas of the X brace as heavily as the rear lower bout sections. 9 months on the top is still perfectly true and there was a definite played in feel almost from the off which is getting better all the time - I have absolutely no idea as to the physics of all this, it seemed to work very well.

Ok this guitar might fall apart in 10 years :shock: but it begs the question about the rational of instruments - the compromise between building light and getting that something extra from the off tone wise v structural integrity - Are our expectations of the 'working life' of an instrument to high - or should we build a 15 years tone monster? ;)
Author:  Todd Rose [ Wed Apr 22, 2009 4:53 am ]
Post subject:  Re: Working the upper "X"
Wes, you could also splay your A braces out wider and run them all the way to the sides at the waist. They could go either under or over the upper legs of the X, depending on how high you want each of them to be where they cross. Done that way (if my elementary engineering thinking is correct), more of the rotational load of the neck block is transferred to the rim and you can lighten up the upper X even more. You could also move the UTB somewhat further north and thereby loosen up a bit more of the upper bout area.

Yet another option is to add struts, aka "flying buttresses", like Rick Turner, Kent Chasson, Howard Klepper, and others. Two struts go from the upper part of the neck block to the bottom of blocks you put in at or near the waist. Check out these photos from Howard's web site to see these struts I mean, along with some other really creative ideas in bracing: http://www.klepperguitars.com/about.html#bracing
Author:  Kevin Gallagher [ Wed Apr 22, 2009 7:21 am ]
Post subject:  Re: Working the upper "X"
Wes,
I was part of the group who came up with that design at Martin back in 1990. They
sell tons of kits every day using that system at the neck block. It was given the name
"cantilever bracing" by someone in the shop and that term stick as they began to offer
it on their guitars in the early 90's.

Are you getting your bracing from Martin through GMC?

Regards,
Kevin Gallagher/Omega Guitars
Author:  Wes McMillian [ Wed Apr 22, 2009 7:23 am ]
Post subject:  Re: Working the upper "X"
Frank, I don't have a hard answer for that. I confess I have my own hesitation to scalloping up there, just due to compromising the structural integrity of the box given the amount of load on the upper bout. I dunno. Like we discuss so often here, everything in building is a compromise, just find what works for you. And it may be that the upper bout can be built even lighter with some alternate method to carry the load up there. My personal feeling is that this is where we all need to listen up to the guys who HAVE been building for decades and HAVE seen the long term effects over the life of a guitar. I would hate to find out several years into my "career" that all my early guitars are now failures due to a too-light build design. Your reputation is everything - hard to build, easy to lose, near impossible to get back.

Now, the buttresses like Todd mentioned and several builders use would probably be an even better design and I've often pondered on doing something like that. I'll bet you could really lighten the bracing with such a design. I confess my biggest hesitation to using them is just simply being able to see these two struts through the soundhole. That may sound like a silly reason but, when you build traditional designs there is a certain expectation. I don't know that bluegrassers, etc, would be very accepting of them just for that reason. Although Mario has proven that bluegrassers today are much more accepting of innovation than in times past but, still, even his guitars are pretty traditional looking from the outside.

Todd, it's conceivable that these struts could run to the waist like the typical flying buttress does. I don't believe it would be quite as effective as the buttress due to not having the triangulated - how am I trying to say this - not attaching lower down in the rims. Running these braces out like you mentioned would allow more of the load to be transferred to the rims but, then, would be adding more bracing directly to the top which would need to be accounted for and built into the "system". It's worthy of consideration - and would alleviate the visual element of the flying buttresses - but I wonder how beneficial it would be. Once again, we're looking for that compromise we can live with. If the typical A-frame bracing is good enough to carry that load (and if anybody wonders, this is just a typical bracing style - not particularly unique to me), then when is good enough, well, "good enough"? I don't know.

I would be interested in people's thoughts on this, though.
Author:  Wes McMillian [ Wed Apr 22, 2009 7:30 am ]
Post subject:  Re: Working the upper "X"
Kevin, you posted while I was writing my "book".

I'm not getting my bracing from Martin (In fact, I'm not sure where this stock even came from. It was part of a package deal on a bunch of stuff.) None of this is from a kit, it's all from scratch and from memory of what I remember that design looked like. Probably tweaked a little here and there, given the condition of my memory. I remember now that you were part of that team and those Martins were the first place that I saw them. The design just made sense from the first time I saw it, and those early 16-series Martins were (and are) very good little guitars. Good job y'all did!
Author:  Frank Cousins [ Thu Apr 23, 2009 2:11 am ]
Post subject:  Re: Working the upper "X"
You speak wise words Wes - about advice especially, but I guess its easier for me to avoid compromise as I am just building for myself and dont reallly have any intention of selling instruments in future. I dont have to worry about that guitar coming back to haunt a warranty list in future ;-) Naturally when you build something, I would love it to last, but as these things are built to play, if the worst happens, I guess I will have learnt from it - I guess my quesion would be to experienced folk, if you were NOT needing to worry about the 'life' span of an instrument and JUST thinking about tone - even if your experience says it wont last 2 years, what would do in this area to maximise the tonal qualities, or would you keep things the same?

I love this kind of discussion because I suspect there will be diverse opinion and thats what means we get such diverse and wonderful instruments from these pro guys - its true what they say, we do live in a golden era.
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