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This is one of the most massive braces on the guitar top and for good reason given the standard conservative (heavy) bracing schemes.

However, many of us are starting to include neck block extensions which IMO take up a considerable amount of the load that would otherwise be taken by the UTB. Plus...I can't remember the last time I adhered to "standard" bracing schemes and I am starting to question the need for such mass here. I long ago abandoned the popsicle brace and lightened up every other brace as well.

My question...has anyone ever reduced the UTB mass and can comment as to what effect it has had. I'm considering reducing it by 50% on my current build (slope shouldered Dred) but wanted to open the issue to some discussion first.

What say you?

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JJ
Napa, CA
http://www.DonohueGuitars.com

Well if you have an “L” shaped neck block that give enough strength to the top to avoid the dreaded fracturing parallel to fretboard and suppress the inward force of the extension then sure. Just keep in mind that the “L” shape creates a cantilever that is many times stronger at the elbow than at the end of the arm yes you can reduce the UTB width and or height. By how much depends on the neck block and the structure of the cantilevered arm. If the "L" shape is gusseted even better

I would question the premise that the UTB in a refined and appropriate size and shape has enough mass to worry about.

If you weigh all of the bracing on a guitar top you will most likely come in at around 40 grams. I doubt if the UTB accounts for 25% of this but let's say that it does. This makes an UTB 10 grams or .35 ounces. Reduce the UTB by 50% and you just saved .175 ounces or 4.96 grams.

I have never weighed a paddle but would guess it to be in the neighborhood of 40 grams also.

If reducing mass is the goal I would suspect that greater gains in reducing mass would be possible by drilling out the paddle and or drilling out the paddle and reinforcing with CF.

JJ ;
do you build classical guitars also ?

The reason I ask is because that area of the top despite much opinion is a dead area that is so to speak cut off from the rest of the top by the S.H. and the lower #2 brace !
I make that area as stiff as i can -I do not want a cave in so to speak !
My guitars have more sustain & solid clear notes everywhere since i started this -I think it's because of the stiff neck & upper body stiffness !
I treat it as dead area -which is good for notes above the body joint !
I've repaired many guitars that were sunken & cracked that was caused by the torsion of the neck onto the body!

I'm replacing a top on a 40's Gibson -it has the smallest braceI've ever seen under the f.b. !
The neck just twisted into the body !
ugly as all heck !
I'm resetting the neck as part of the repair !

Mike

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Mike Collins

Hesh...Actually, the goal is to squeeze more tone out of the UB...if that's even possible. There definitely is a difference when the popsicle brace (AKA mass) is removed so theoretically there should be a difference if mass is removed from the UTB. The UTB on a Dred is massive (5/8" x 1/2" x 11" - taper and rounding) so it's probably more like 20 grams And if it's 10 grams out of that brace, I would consider that substantial in making that portion of the top accelerate faster.

Michael...the neck block extension is 3/4" baltic birch to which the top is glued. The arm ends about 1/8" from the UTB. There then is a considerable portion of that block that is removed to accommodate the FB tenon. One consideration is whether to bolt the FB down until only the FB tightens against the top or to tighten such that the tenon bottoms out inside the mortise...but that's still another experiment under consideration.

Any thoughts from those who have actually used bolted on FB extensions?

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JJ
Napa, CA
http://www.DonohueGuitars.com

You did not mention any gusseting taking the load from the end of the cantilever and returning back to the vertical mass of the neck block. Because of this I would not reduce the UTB more than 10% the machining you did to insert the extension tenon (if I read correctly) reduced the amount of resistance the cantilever gives against the inward rotation of the extension. It does had some reinforcement but only equal to its thinnest segment.

Mike...I don't build classical guitars. From what I gather, there might be 2 schools of thinking about the upper bout...those who try to achieve a dead zone and those who try to squeeze tone. I guess I fall into the latter category mainly because I'm not aware of what is impossible...yet.

I hear you about the rotational forces of the neck though and it is the obvious risk of not having sufficient reinforcement. Hopefully, we can approach the line without falling off the cliff. On this particular build, I have stiffened the upper bout significantly by double layering the side from the neck block to just north of the waist (a clever Mario idea that he includes on his latest guitars). In addition, I have laminated CF to the X-braces which is intended to add further stiffness than normally found in the UB on standard bracing. I could even go further by providing a super stiff but lighter UTB as well. Right now I'm open to ideas.

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JJ
Napa, CA
http://www.DonohueGuitars.com

JJ,

I'm in the all other things being equal (and they never are) "lighter is better" camp, so my answer is prejuduced by this perspective. I've spent a great deal of time studying old instruments both through photographs and examination of actual instruments when lucky enough to find them. My focus is mainly late 20's and early thirties Martins, and that's the tonal envelope I'm trying to emulate. I keep on my bench an upper transverse brace from a 1932 Martin 000 whose top was replaced for non-structural reasons. It measures .245 x .498. It is perfectly QS spruce, but it looks like a toothpick compared to most of the UTB I see. It served it's purpose for more than 60 years without any measureable deflection that I can see. This dimension was pretty typical for the Martin line (even dreadnaughts) during this time period and there are still plenty of these guitars being played today. It's not to say many, if not most, haven't had a neck reset, but I'm not convinced the UTB has much to do with it.

The forces that lead to the distortion of the top are a complicated set and I don't begin to know all the answers. I'm of the opinion that the rotation of the neck block is the major cause of top failures and that the UTB plays only a minor part in the structural integrity of the box. In order for the UTB to be a major player, you'd have to depend on the FB extension to be absolutely ridgid and force the UTB towards the back. Even bound fingerboards don't have much structural integrity over the body, so they don't have much impact on forcing the UTB down. It's the upward pull at the neck joint that exerts the most force and block rotation that pulls the arch out of the back that causes the need for most neck resets. In the 60's, most neck resets involved "slipping the block" where the neck block was actually separated from the back and rotated back to it's original position. This was done to correct the neck block rotation. I should note that the neck joint may have some effect on this and my answer is based on a dovetail joint. I suspect that the same forces are present in all neck joints to some extent.

An "L" shaped neck block would seem to me to exacerbate this situation as there might be a possiblity of the block rotation actually pulling the top down with it. I have seen the use of carbon fiber rods to prevent this rotation and that seems like a reasonable approach to me.

Anyway, that's $0.02. I'm sure others have varying opinions.

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Jimmy Caldwell
http://www.caldwellguitars.com

Well then grasshopper, why not take the step of taking the forces applied by the neck/strings on the neck-block into one of the strongest parts of the guitar - the rim-set - via flying buttress braces rather than building a cantilevered extension to the neckblock that is still attached to the top?

Then deliberate the next interesting question of what to do to the upper bout bracing to extract the tone subtleties you seek - more, less, none, different ?

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Dave White
De Faoite Stringed Instruments
". . . the one thing a machine just can't do is give you character and personalities and sometimes that comes with flaws, but it always comes with humanity" Monty Don talking about hand weaving, "Mastercrafts", Weaving, BBC March 2010

Great historic info, Jimmy...Thanks...and that's the kind of factual data I really appreciate. As far as the neck extension exacerbating the rotational problems, I'm hoping that the super stiff sides will resist the torque much like the CF buttressing is intended to address.

Dave...I was hoping you'd chime in !! I think the reinforced sides (rims) address your point and in my opinion a simpler solution.

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JJ
Napa, CA
http://www.DonohueGuitars.com

JJ,

Are you sure just the stiff sides on their own will stop any relative movement and twist of the neck block over time (months/years) under constant string tension? I suppose you could rig up a test. It will be interesting if Howard Klepper joins in as he does double sides and - I think - still uses flying buttress braces.

If the stiff sides are taking all the tension/compression then surely your question about the utb dimension is all about tone and not about structural integrity.

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Dave White
De Faoite Stringed Instruments
". . . the one thing a machine just can't do is give you character and personalities and sometimes that comes with flaws, but it always comes with humanity" Monty Don talking about hand weaving, "Mastercrafts", Weaving, BBC March 2010

Dave...if I were sure about the double sides being enough on their own then I wouldn't need to seek opinions from guys like you.

I hope Howard chimes in and I really would love to have Mario discuss his experiences as well. In the end, we go with what our best intuition tells us and a lot of that just happens to be the faith in ideas by those who have made advances before us. I'm less worried about the rotation issues as I am about how much UTB mass reduction to go for. Shoot...it's just a guitar! If it doesn't implode in a year nor change its geometry significantly, then we'll have moved the body of knowledge a bit further down the road. Seems like each guitar I've built in the past 4 years has something new and different to consider. This is just another new issue to follow over time.

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JJ
Napa, CA
http://www.DonohueGuitars.com

JJ - Great question. I have been mulling this over myself as i'd like to do the routed neck extension and was wondering if i could eliminate the UTB altogether if i used the CF rods from the extension to the sides (Dave W. are those the "flying buttresses you refer to?).

The one question is would also have is how much does the UTB preserve the radiused top and is that a good thing to continue?

Rob

You can gusset the neck block extension until you can stand on it, but without the UTB you aren't supporting the top on either side of it, where the neck block extension is pulling the top down from string torque. You also still have a big stress riser running parallel to the grain along the edges of the block extension. I think with no UTB you will just move the location of the dreaded fingerboard side crack out to the side of the block extension.

I think the UTB is of great structural importance. I usually top it with carbon fiber, and also use carbon fiber struts to transfer string load to the sides just below the waist. At some point making it bigger is overkill, but in this discussion, I'm with those who don't think reducing mass in the UTB is going to get you much sound.

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Howard Klepper
http://www.klepperguitars.com

When all else fails, clean the shop.

Rob...I'm not brave enough to propose eliminating the UTB altogether...just reducing the mass.

As far as preserving the top's radius, I'm one of those whose UTB is NOT radiused, but flat. Having the UB flat allows the FB to fit better to the top.

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JJ
Napa, CA
http://www.DonohueGuitars.com

Howard...thanks for weighing in on this. Just to clarify...I'm not proposing to eliminate the UTB...just reducing mass.

In addition to your CF struts, are you doubling your sides in the UB area as well?

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JJ
Napa, CA
http://www.DonohueGuitars.com

Jimmy, I appreciate the info you shared in your post. I learned a lot reading it.

Regarding the neck block rotating, I have a question. Would the neck block rotate easier when the back is more radiused than it would if built flatter? It is popular to build backs with a 15ft radius which I've read is nice for moisture changes but I'm curious how well it resists neck block rotation. Does anyone brace a 15ft radius back differently to resist neck block rotation?

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Formerly known as Adaboy.......

Darryl,

I have been using a compound radius on my backs (flat at the Back version of the UTB and gradated more as you go back with no taper towards the sides on the waist brace) in order to try to lessen this effect but none of them have been together long enough to give much response as to its long term benefits.

I think that a strong and stable neck joint is a combination of well matched braces and bracing decisions. A strong UTB with a stiff FB glued to the top, a strong heel and neck block, and a well braced back on a proven design has been shown to hold up reasonably well over time. When you begin to change any one of those variables though I think another must change with it. I don't think of double sides as adding much insurance to the situation and I don't think the flying buttresses addresses completely the problem of the back flattening.

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Burton
http://www.legeytinstruments.com
Brookline, MA.

I use a bolt-on fretboard extension and reinforce the top brace with an inset carbon bar. Hopefully I'll live long enough to see if it helps.
TJK

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It's not what you don't know that hurts you, it's what you do know that's wrong.

In the design I'm currently developing (prototype is under construction), I've run a big brace down the center of the back, where you'd normally have a centerseam graft. It's 3/4" wide and roughly 1/2" tall at it's tallest, tapering down to about 1/8" tall at each end. It's radiused on the bottom - 15' (like all the other back braces) - and flat on the top. It's also capped with .030" CF. It is a stiff mother. I don't think that back is going to be flattening.

This design has an elevated, floating FB extension. There are CF struts running from the top of the neck block to the bottom of the waist blocks, and from the bottom of the waist blocks to the top of the butt block. The back also has a CF capped transverse brace at the waist to help keep the waist from spreading and flattening under the load of the CF struts on the waist blocks.

There is a UTB on the top, but it's up really high in the upper bout, right up against the neck block (which does not have a foot). There are also two A frame type braces in the upper bout going from the neck block to near the waist. I believe a larger area of that upper bout is more free to vibrate than in a traditional design, while the structure of it will be plenty strong.

In a more traditional design with the FB glued to the top, I'm with others in the observation that the FB extension on a strong UTB is a very important structural arrangement. A foot on the top of the neck block can be part of that structure, but the UTB is still, I believe, playing a critical role. Also, I don't see how you gain much in vibrational potential by lightening up the UTB, if the FB is still glued to the top (and/or if you have a big foot on the top of the neck block). Uh-oh... Big Foot... watch out...

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Todd Rose
Ithaca, NY

https://www.dreamingrosesecobnb.com/todds-art-music

https://www.facebook.com/ToddRoseGuitars/

Todd, I think the struts from the neck block should attach a bit below the waist. That way the load is aligned with the side below the waist and doesn't push the waist out.

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Howard Klepper
http://www.klepperguitars.com

When all else fails, clean the shop.

The popsicle stick brace was never the best design, but getting rid of it and not having anything to supplement the UTB is much worse. You need support up there, and a lot of it in my experience. The sides don't do the job themselves.

Here's one that came in the other day.





I actually see this a lot, where the shoulders essentially collapse and pucker inward at the corners of the neck block (or sometimes at the heel, leaving the neck block separating from the sides). The top in the shoulder area either bubbles up in to a big hump or just sheers at the edges of the extension and slides in to the soundhole. I have at least one other in that has slid much further, but didn't take any pics, and that one does have a popsicle stick brace. The popsicle stick is actually not flawed because it is redundant or too much, but rather because it is not enough. I'm all for getting rid of it in favor of better styles, but you definitely need a lot of support there.

If you don't get the sheer collapse like this, you'll at least get the bulge and hump. It may take 20 years to happen, but it will come. Areas like this rarely fail immediately when under built, but prove to suffer when time is added to load in the equation.

If you want to lighten that area, you can't do it by simply removing material from an already under-supported area. If you want lighter, you have to rethink the design and brace smarter. There are lots of improvements over traditional shoulder bracing out there (struts, buttresses, A-frame, use of carbon fiber, etc), but that's an area that can't afford any less support than it already has.

If you want to lighten a highway bridge by 50%, you can't just use half the steel and concrete. You have to totally rethink the traditional design.

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Eschew obfuscation, espouse elucidation.

Good info as always, David. Your examples are indeed sobering and will go a long way in helping me to settle on a final design.

As part of my bracing scheme when I have removed the popsicle brace, I added "A" braces to span the distance between the UTB and neck block. I guess time will tell whether that helps to prevent or delay the issues that you show. In my current design, the neck block extension ends rather close to the UTB and acts as a support area in addition to providing a mortise block for the FB tenon. On the other hand, I have seen guitars where folks have used 2 UTBs so I realize that I'm playing well on the other end of that spectrum. It looks like I may be moving more toward the center...it's just a matter of how far right now.

Thanks for posting...lots of opinions to weigh. To me, these brainstorming exercises represent the best of forum interchange.

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JJ
Napa, CA
http://www.DonohueGuitars.com

Your A-frame replacement to the popsicle stick is almost certainly an improvement - the popsicle stick just really didn't provide support in the direction it was needed, and seems only to have been a solution to a symptom of sheering tops.

I'm also of the camp that does not credit the upper bout with a tremendous amount of responsibility for driving the air. Still, if you do want to try lightening it up I would go with many of the above ideas for lightening by redesigning, and not just removing material without any supplement. Struts, buttresses, carbon fiber, double sides, all great ideas that I have little experience with. I guess if I don't see them often though that means they're probably working so far, as I only get to see stuff when it fails.

Incidentally, the guitar pictured above actually did have a kind of A bracing, though actually more of a V. They start outside the frame of the picture and spread out wider as they approach the shoulders. Don't ask me what they were thinking there.

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Eschew obfuscation, espouse elucidation.

Darryl,

Theoretically, the less radius the back has the less there is to be pulled out, but I'm not certain that translates into reality. As I said, there are a lot of forces going on and addressing just one of them may lead to those forces being transferred to another component in ways which are hard to predict. FWIW, I radius my backs to 15' like most, and will continue to do so.

As far as the UTB goes, again I don't believe it's a major component of the structural integrity of the box. That doesn't mean it doesn't have a role and I would certainly not advocate eliminating it. It's a part of the equation, how big a part is the question.

To address the problem David has cited with the splits in the top, I've gone to using a trapezoidal piece of spruce ~ .10 that starts at the neck block and terminates at the UTB. It's slightly wider than the neck block where it begins and slightly wider than the soundhole when it terminates at the back of the UTB. I use a cutoff from the top and run the grain parallel to the top grain. I got this idea from a post by John Arnold over on the UGMF. I've only recently started using this approach, but it makes sense and will hopefully help prevent the type of cracks we typically see on either side of the FB.

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Jimmy Caldwell
http://www.caldwellguitars.com