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grumpy,
   I believe what everyone is shooting for with these efforts is to minimize,
and ultimately eliminate, the "collapsing" or "caving in" of the guitar along
its top that comes with time under string tension.

   Every old Martin, Gibson, Guild or other maker's guitar that i've ever
played has exhibited it and the most common result brought about by it
is the need for a neck reset and all of the changes from original specs
that it brings.

   The same is true of many guitars from just as many of the modern
builders who have popped up in the past few decades. I've played...and
reset necks on alot of relatively new guitars from builders who are well
known and have strong following.

   That span from the nut to the saddle supporting string pulled to
concert pitch is really too much for a guitar to withstand for any length of
time without surrendering to it...at least in some way and to some
degree. That is, if the guitar is built to dimensions, weight and of
materials that will allow it to efficiently operate as a tone creator.

   I've seen some, on the other hand, that were built very heavily in an
effort to avoid future returns for warranty work for their builders....and
they even shown some of the movement.

    I've done some of the veey same things that have been posted on this
topic recently and have enjoyed some of the results, but never enough for
me to start implementing them on my guitars....yet. I have a few ideas in
prototype now that i may use on every guitar in the future, but i'll have to
wait to see what they sound like before I do. I don't want to use any of
them just because they look coo or because I thought I had a great
idea...that fifty other people probably had before me.

Regards,
Kevin Gallagher/Omega Guitars

   

My I ask, and I ask this in total honesty, so don't anyone get all worked up, what the end goal is?

Good question.  My goal with this is to be able to build a relatively conventional guitar and be able to think of top thickness and bracing almost entirely as tone control rather than structure.  Right now that mostly means simply building a little lighter than I have previously without having to worry about neck re-sets.

At this point, I'm still gluing the fretboard to the top so I'm not even trying to eliminate the upper transverse brace and activate that area as Rick and others do.  But I did scallop the ends of the UTB more heavily than I otherwise would and I could hear the tap tone in the area just below that brace open up quite a bit.  This one has yet to be strung up but all indications are good.

Personally, I like the sound of relatively conventional/traditional guitars and am not trying to make something that sounds radically different.  I just want more of what's there.  But if I ever want to really start messing with new bracing concepts, this seems like a good way to create a fairly blank slate to start from by taking a lot of structural considerations out of the picture.

I've also had the experience that anything I do to stiffen the rims adds power and hurts nothing.  This certainly adds stiffness and is way easier and probably lighter weight than laminating sides.

And so far, the banjo analogy (soundwise) is not even in the picture.

_________________
http://www.chassonguitars.com

The only concern I had was that there is actually no rigid link in the system that is under pure compression, so the resistance to moving the tail closer to the neck here is carried by the joints in the waist block, rather than the rods themselves (i.e., it the rod ends were pinned rather than fixed, the structure as shown could still collapse.)

I'm not sure I get what you're saying.  The rods are certainly capable of bearing a large compressive load and they seem to transmit the load to each other efficiently through the blocks at the waist.  Spanning only to the waist and not all the way to the tail makes it a lot more efficient in my mind.  (Deflection of a simple beam increases by the square of the span, is that right?)

Without the top on, I could squeeze as hard as I wanted and could feel no flex in the system.  The back could possibly flatten out over time but I personally don't want to make it so stiff that it becomes inactive.  As long as the heel and tail blocks have enough glue surface to hold the shear force, I can't imagine it going too far.

_________________
http://www.chassonguitars.com

Well said, Kevin and Kent!

I think my biggest surprise in building a steelstring guitar that was engineered radically different than anything I had ever seen, was that it sounded like a steelstring guitar. I'm not being flippant, I had heard terms such as "piano-like" used to describe Kasha guitars, and was not too sure what sound I would get. I now think the shape and volume of the box are the major criteria in determining what I would call the "big picture" timbre of the guitar, and the "color" of that timbre (and some other qualities such as sustain) are probably quite a bit more moldable/shapable than anything possible by merely refining the Martin standard.

Dennis

_________________
Dennis Leahy
Duluth, MN, USA
7th Sense Multimedia

I understand, Kevin, but where are all these collapsed guitars? Yes, I've seen a few that have sunk a bit, and one that completely imploded(a cheap plywood guitar), but by far, it isn't such an issue that it deserves a complete re-thinking. The folks that produce the most guitars, Martin, Taylor, Gibson, and the countless Asian mega-factories, would have surely "fixed" this problem. Especially Bob Taylor...


So, since the problem only happens with a precious few examples of guitars, that's not it. A least, not if we don't allow ourselves to go warranty-paranoid. And i'll go out on a limb and say that all of this won't eliminate the need for small neck angle corrections, because the rest of the instrument will still move a bit with time, and we know that neck block movement isn't the major cause for neck resets, but rather, the whole of everything moving in nearly non-measurable amounts... A hollow CF rod inset into a wood block, under compression, will move with time, and epoxy can creep. The surface area that th tube bears against the wood with is very small, and wood readily compresses... and CF is strong and very stable in tension, but not so much in compression(although it is still very strong there, just not as much). Small bars of birch ply could actually be better and lighter here. But certainly not as cool.

But the real reason for my asking was, what are we expecting to be able to do with the guitar, with this engineering? Never mind the structural issues that may or may not arise with regular guitars. What part of all this will help the player enjoy it more? Why will the player grab this guitar over one built conventionally? Will it sound so much differently that the audience will insist their favorite musicians use one?

As Dennis noticed, it's pretty tough to make a steel string guitar that in the end, doesn't sound like a steel string guitar. So, where else can it go? Where are we trying to take it to, I guess, is what I'm asking?
 

it isn't such an issue that it deserves a complete re-thinking.

I didn't know this was a complete re-thinking.  It's a pretty simple add on.  Neck re-sets aside, I've found that stiffer boxes make a more powerful guitar and that alone would justify it for me.

The folks that produce the most guitars, Martin, Taylor, Gibson, and the countless Asian mega-factories, would have surely "fixed" this problem. Especially Bob Taylor...

Maybe.  But I don't see any of those big companies pushing the limits of design either.

Maybe someone with factory experience can speak with more authority but I assume that any large factory builds to dimension rather than stiffness.  This means that they have to thickness their tops and shape their braces based on the least stiff wood they plan to use.  And they use so much wood that they are bound to get drastic variation.  This would mean that the majority of their instruments are overbuilt to begin with.  That also explains why two "identical" factory guitars hanging on the wall at your local store can sound so different.

As a small builder, my goal is to push the limits and try to get everything out of each instrument that I can.  That means building closer to the edge.  This seems like cheap insurance.

A hollow CF rod inset into a wood block, under compression, will move with time, and epoxy can creep. The surface area that th tube bears against the wood with is very small, and wood readily compresses

In theory maybe, but you are talking truly microscopic amounts compared to traditional construction.  The bearing surface in mine is eastern maple and the the holes are filled with epoxy.  There is absolutely no way that any element of the system will "readily" compress with the loads involved.  You know the difference in rim stiffness going from kerfed to solid linings?  This is orders of magnitude beyond that for a very small price in weight and time.  And the weight could even be offset by a smaller heel block.

I haven't tested this enough to incorporate it in all my guitars yet but so far I'm asking, given the added insurance, the added stiffness, the added design flexibility, why wouldn't you do it.

_________________
http://www.chassonguitars.com

Kent,
   You're exactly right when you say that the large houses buold to
dimension and not according to the stiffnes or resnonance of any of the
components at hand.

   I can speak from experience for the Martin shop. There was a time
when a craftsman would examine each part of the guitar that was on his
bench and would consider its resonant qualities and stiffness as he chose
the edjacent componants according to how they would work together and
compliment opne another, but it has been a very long time since that was
a practice in their shop.

   With the huge demand that they have to meet on a daily basis (more
than 500 guitars a day), the possibility for time to be spent on such
charming and romantic facets of building is a thing of the past.

    The sheer numbers of guitars that Martin has produced has established
their models and design details to a point where general consistency
comes from the dimensions and material choices that they've arrived at.
Things are production oriented, as automated as possible and quota
driven for a large part. I remember back in the early 90s when each
department was plastered with several dry erase marker boards with
statements to the effect of, "Today's production...300 (for example)" and
"Tomorrow's goal...325 (for example)." A few of us recommended against
it for the sake of the tour groups that were usually filled with folks who
were 2nd, 3rd and 4th generation Martin enthusiats and still had the
romantic vision of lone luthiers huddled over the worn work benches
hand carving braces and such. They didn't last long and you don;t see
them on the tour route now, but the numbers are still clearly
communicated to the employees of each department nonetheless.

   There are very few employees out of the hundreds working there who
can actaully build an entire guitar from start to finish...probably under a
half dozen. The balance of employees have been trained to do one...or a
few....specific steps or operations in the build process in order to make
them "specialists of sorts. The few who inlay rosettes, do so very well and
very quickly. Those who brace tops and backs, do them well and very
quickly. The list goes on of specific steps that are done as quickly and
neatly as possible to keep the parts moving toward being added to the
assembly of the guitars.

   When a top or back or a set of sides are chosen for a guitar, they aren't
tapped and then matched with bracing that will contribute to the strength
of the braced top according to its stiffness or will compliment or balance
the tone of the braced top after they're joine to one another. The parts
are simply grabbed from the top of the stack or box next to the bench
and glued up as quickly and neatly as possible. That goes for all
components that are generally considered major tone contributors...like
tops and their braces....as well as more passive components.

    Stiffness and resonance variables are within a range that allows this
kind of random selection to present fairly consistent tone and stiffness
and the well establiched body shapes and dimensions keep everything
within what has become the expected and signature tone of a Martin
Guitar.

   They don't have time to push the limits of design too much simply
because what they do has been working well enough to keep their guitars
in demand. They do try new and different things occasionally, but the
underlying structural and design ideas remain inside the Martin box.

    They're building wonderful guitars here in Nazareth, but they're
building alot of them every day and in avery different environment than
many people envision.

Regards,
Kevin Gallagher/Omega Guitars

Kent, thanks for posting the pic. That looks great, and makes perfect sense to me.

_________________
Todd Rose
Ithaca, NY

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

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

This is a very interesting thread to me and I have been really considering the many excellent points that many of you are making.

Kent when I saw your photo above it reminded me of a book that I am currently reading by David Pye.  Pye indicates that he will not attempt to define the difference between "workmanship" and "craftsmanship" but he is clear that craftsmanship should be considered the pinnacle of workmanship.

I see some real craftsmanship in your work and design.  Beautifully done, very simple, and with only a 50 gram increase in weight that is probably more than negated by the added rigidity and possibilities for thinner tops and bracing.

Somogyi as we know uses very thin tops but we also know that he is able to do so by greatly stabilizing the rim with double sides.  Rick also stabilizes the rim with a partial double side with an added strip toward the top of the sides.  In addition, if I have this correct, he employs CF strips to line the kerfed linings.

What caught my attention the most here is Kent's statement that he wants the top to be more of a tone influencer and less of a structural component.  Again considering how Somogyi, and Rick stiffen the rims of their guitars I think that all three of you are working to free up the top to be primarily engaged in tone/sound production. 

A nit that occurred to me is how the CF rods go from the top of the neck block, to the back side of the waist, and then to the top of the tail block.  Why didn't you run the CF rods as they are but to the top, front side of the guitar, of the waist blocks?  It seem to me that this would be more rigid, the rods would be shorter, and the angles more direct with the compressive loads?  This is not a criticism it's an inquiring minds want to know question.

I also wanted to ask a question about how the rods are anchored.  I understand what you have done for compression and wanted ask if anything is done to the ends of the rods to resit pulling - perhaps roughing them up at bit?

Lastly for me tonight Mario's point about what are we trying to solve here is a good point.  Traditional designs do work very, very well considering that it is indeed true that it is not difficult to make a guitar sound like a guitar.  And is it unreasonable to just accept that somethings will need adjustment over time.  It seems that all things do.......

What I see in your design Kent is not unlike when architects discovered that buildings could become much taller when the outside walls were no longer depended upon as the primary load bearing structures.  Instead inner structures where employed to provide the strength to go higher and the outsides became a skin of sorts.

I like what I see with the CF internally supporting the rim in your, Dave White's and Rick's guitars very much.

Nice work.

Actually, my query wasn't meant to question validity, as much as it was to bring out the why's and wherefor's. And to make everyone ask -themselves- "why".

Ever see someone who's upset beyond upset? Next time, just calmly ask them why they're so upset. If they just spout out explicitives, keep asking, calmly, why? Eventually, odds are, they will realize they're a lot more upset than called for <g>. All because you asked them to stop and explain; and in order to finally explain to you, they first had to explain to themselves, "why". Learn by teaching, and we begin by teaching ourselves.

We've had a few "for why" answers, and they're good ones.
I'm sure there must be more; let's here them, and don't get defensive, there are no bad answers.

For me, Mario, there are two basic issues:

1) To prevent the distortion over time that results in the rotation of the neck block which changes the neck angle, and to accomplish that without needing to use the top and it's upper bout bracing to support the neck and fingerboard.   I've seen that that approach does not necessarily work over time. Using flying buttresses stiffens up the structure with very little weight penalty, and that weight is not attached to the top.

2) To free the upper bout of the top for possible tone production beyond what is normal for guitars with the fingerboard glued and/or screwed to the top.

Structural improvement over the long haul and a greater range of tonal possibilities; those reasons are very clear to me.

If you decided that you like the sound of a guitar with a blocked up upper bout, you have that freedom...and you're not going to worry about neck resets, either, so you can build quite lightly, if that's your thing. So far, building lightly has not been my thing, but I'm certainly going to try it, but I'm not giving up my flying buttresses; they work too well.

I'm starting a classical guitar project with a marvelous Southern California luthier named Monica Esparza.   We're going to see what happens when a Romanillos-trained guitar maker teams up with an unorthodox luthier like myself. We're both pretty excited about this collaboration, and I know I'm going to learn a lot from her on this guitar. We don't quite know how far we're going to push it, but we both want this to be something we can hand to a "real" classical guitarist without the guitar being off-putting.   But with Humphrey, Smallman, etc. out there, we have some good wiggle room with the design, yet it will look very classical from 20 feet away.

grumpy,
   When I said "collapse" or "caving in" I meant the sinking that is typical,
not an actual implosion like we've seen with those cheapies from overseas
that can actually come apart under stirng tension.

   I agree that we're not going to eliminate this rotation of the neck block
that is allowed by the flattening of the back arch which makes possible a
longer dimension and the sinking of the top that makes possible a
corresponding shorter dimension and the leaning forward of the neck.

   I like hearing about the ideas that others have in trying to avoid it, but I
don't spend alot of time on it.

Regards,
Kevin Gallagher/Omega Guitars

Kevin, I do not agree "that we're not going to eliminate this rotation of the neck block that is allowed by the flattening of the back arch which makes possible a
longer dimension and the sinking of the top that makes possible a corresponding shorter dimension and the leaning forward of the neck."

I know that we can eliminate that rotation through the use of basic engineering principles that are quite easy to accomplish. Several of us here have built guitars that achieve this goal quite nicely. You've got to feel how stiff the rims can be to believe it, but the improvement is dramatic.

[QUOTE=Kent Chasson]

The only concern I had was that there is actually no rigid link in the system that is under pure compression, so the resistance to moving the tail closer to the neck here is carried by the joints in the waist block, rather than the rods themselves (i.e., it the rod ends were pinned rather than fixed, the structure as shown could still collapse.)

I'm not sure I get what you're saying. The rods are certainly capable of bearing a large compressive load and they seem to transmit the load to each other efficiently through the blocks at the waist. Spanning only to the waist and not all the way to the tail makes it a lot more efficient in my mind. (Deflection of a simple beam increases by the square of the span, is that right?)

Without the top on, I could squeeze as hard as I wanted and could feel no flex in the system. The back could possibly flatten out over time but I personally don't want to make it so stiff that it becomes inactive. As long as the heel and tail blocks have enough glue surface to hold the shear force, I can't imagine it going too far.

[/QUOTE]

Kent - this concern was overkill on my part.

Imagine that your two carbon rods in the span were simply hinged at the waist rather than having ends embedded in the block there. The rods by themselves couldn't carry any compressive load - if you pushed on the ends, the ends would simply mover towards each other.

If, on the other hand, you tied this pinned joint to the other pinned joint on the other side of the guitar using a crosspiece, then you'd have a truss formed by two triangles sharing a common member - the crosspiece. You could then load this up under compression or tension anyway you want.

Mario's point is well taken about this being a lot of engineering for something that basically works to start with. It's not clear to me that all of this unloads the top of a conventional pinned or tied bridge guitar in a way that gives you an immense amount of extra freedom to play with thickness or bracing. The string load is still getting applied at the same point, it's still the same amount, and the shear and torque on the top are the same.
Until that is changed, the bracing requirements in the bridge area are still pretty much the same. Torque could be fought using a Bridge Doctor. I'd still like to see what in-plane stresses look like - maybe over the Christmas break...

_________________
Jim Kirby
kirby@udel.edu

Jim, you'll notice that in the other thread where this is discussed my guitar has a carbon fiber topped back cross brace at the waist very close to where the flying buttresses are anchored. That brace carries some of the tension load from the splayed braces, but also that compressive force is being taken by the shear strength of the sides which below the waist are nearly in line with the buttresses.   

One of my points is that this is pretty simple engineering for something that basically doesn't work to start with, to flip your words around. This is where having hundreds and hundreds of guitars come across one's repair bench over many years kicks in. I dare say most of the luthiers here are not and have never been commercial guitar repair men and women.   The range of experience with long term guitar failure is very limited here in the OLF.   It's easy to think that "it all works" when you haven't had instruments that you've built come back for repairs because the instruments simply haven't been out there for very long.

The flying buttresses are no big deal to install, and they work to strengthen guitars against real world problems.   This isn't theory or imagination or finite element analysis talk; it's been there done that fixed that don't want to see that happen with my guitars talk.

Rick -

Yes, I know what you're saying, and agree. I was just wondering more if this type of support buys any more freedom to play with the top in terms of thickness and bracing. I was thinking that it doesn't, unless the string load is transmitted to the tail instead of the bridge somehow.

Heh, were you involved in designing "The Wall" for the 1974 GD shows? That was a pretty incredible thing to see from the audience side.

_________________
Jim Kirby
kirby@udel.edu

I see some real craftsmanship in your work and design.

Thanks Hesh. I wish I could take credit for the design but I can't.  It's just going the next step from the neck block rods.  I've never seen someone continue to the end block that way but I'd be really surprised if it hasn't been done.

Why didn't you run the CF rods as they are but to the top, front side of the guitar, of the waist blocks?  It seem to me that this would be more rigid, the rods would be shorter, and the angles more direct with the compressive loads? 

I'll give an over-simplified answer based on extremely limited engineering knowlege...running them at a diagonal actually does put them more in line with the compressive loads which I think would be at some kind of vector closer to 45 degrees to the top rather than parallel to it.  Under string tension, the top of the heel block is trying to rotate down more than it's trying to push straight back.  Also, as Rick has said in another thread, triangles are inherently structurally rigid.

I also wanted to ask a question about how the rods are anchored.  I understand what you have done for compression and wanted ask if anything is done to the ends of the rods to resit pulling - perhaps roughing them up at bit?

They are just epoxied in but there's no possibility for tensile loading that I can see.

Mario, I appreciate the "why" questions.  I always try to think from the end result and work back but being reminded can never hurt.

I know that we can eliminate that rotation through the use of basic engineering principles that are quite easy to accomplish.

Rick and Kevin, that's a question for me.  Sure we can eliminate it for all practical purposes but it seems to me that means either making the back totally rigid (not sure I can get the sound I want by doing that) or go to extremes to make the rims more rigid.  At this point, the buttresses seem to take care of the vast majority of the potential movement but, as Kevin said, my conventional back could still flatten out.  This may be getting past the point of "who cares" but I'd be curious to hear thoughts on simple architecture that would allow a lively back while stopping end block spreading from that side.

It's not clear to me that all of this unloads the top of a conventional pinned or tied bridge guitar in a way that gives you an immense amount of extra freedom to play with thickness or bracing. The string load is still getting applied at the same point, it's still the same amount, and the shear and torque on the top are the same.

For my purposes, that's what I want.  I'm of the belief that it is exactly this stress that makes a guitar sound like a guitar.  Freeing the top of the structure required to overcome the long term, "plastic" deformation induced by string pull is what I'm after.

_________________
http://www.chassonguitars.com

I'm not doing this for the lower bout of the top; I'm doing it to free up the upper bout which in conventional guitars is saddled with the responsibility of supporting the neck and fingerboard. At this point, I don't care to change the basic way the string pull acts upon the bridge as that may be essential to making a flat topped guitar sound like a flat topped guitar rather than a Macaferri, for instance.

The back doesn't have to be absolutely rigid. You could run a tension rod just above the back braces ala Larson. that would lock the neck block from rotating. The flying buttresses would be in compression and the rod would be in tension. You could do it with a nice 1/4" CF tube epoxied into the neck and butt blocks.

I'm building with an adjustable neck joint and elevated/floating fretboard, working with concepts similar to Rick's (inspired by Rick and others).

Here's my "new" idea that I came up with this morning (I put "new" in quotes, because I'm guessing it's been thought of, and perhaps tried, before). It's along the lines of what Rick described in his last post above (the Larson tension rod thing), but with a "new" twist:

Build a stiff rim with CF structural members like in Kent's photo above; I think I'd add a CF capped cross brace to the back at the waist, as Rick does, to add tensile strength there to help counteract the two waist blocks wanting to spread apart from each other (and consequently flatten the dome of the back crosswise) from the force of the CF rods. NOW, make my neck angle adjusting bolt into a long tension rod that goes all the way from where it threads into the heel, right down through the center of the guitar and THROUGH the butt block. The neck angle is now adjusted at the butt end of the guitar (on the outside of the box), and the pull of the heel is anchored there rather than at the bottom of the neck block. I'd probably come up with a way to make the neck angle adjusting bolt head on the butt integral to the strap button (while adding a separate jack for pickup wiring).

Have I explained this clearly? What do you guys think?

_________________
Todd Rose
Ithaca, NY

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

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

That will work...

Keep it low on the body toward the back just above the back braces. Recess it into the end of the guitar, and don't use it for the strap pin as so many pickups come with integral strap jack/preamps. You could weld a stainless steel Allen head bolt to the rod and just have the Allen head showing flush with the end of the guitar.

One thing I might not have explained well... this tension rod/neck angle adjusting bolt would pass right THROUGH the neck block as well as through the butt block. The only force exerted on the neck block by the neck would be at the top of the block where the heel bears on it. (I'm not bothering to explain here the detail of how the top of my heel bears against the neck block; that's beside the point.)

One more thing that may help you visualize this is that, in my design, the entire heel is mortised into the neck block. Unlike Rick's cool adjustable neck joint, none of the hardware is visible from the outside - nor is it accessible from the outside, unless I incorporate this new idea of extending the adjusting bolt all the way through the guitar and out the butt.

_________________
Todd Rose
Ithaca, NY

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

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

Fast response, Rick. Thanks! You posted while I was typing my addendum there...

_________________
Todd Rose
Ithaca, NY

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

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

[QUOTE=Rick Turner] That will work...

Keep it low on the body toward the back just above the back braces. Recess it into the end of the guitar, and don't use it for the strap pin as so many pickups come with integral strap jack/preamps. You could weld a stainless steel Allen head bolt to the rod and just have the Allen head showing flush with the end of the guitar.[/QUOTE]

Thanks again for these thoughts, Rick. What's the reason for necessarily keeping the rod "low on the body toward the back just above the back braces"?

_________________
Todd Rose
Ithaca, NY

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

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

[QUOTE=Todd Rose] [QUOTE=Rick Turner] That will work...

Keep it low on the body toward the back just above the back braces. Recess it into the end of the guitar, and don't use it for the strap pin as so many pickups come with integral strap jack/preamps. You could weld a stainless steel Allen head bolt to the rod and just have the Allen head showing flush with the end of the guitar.[/QUOTE]

Thanks again for these thoughts, Rick. What's the reason for necessarily keeping the rod "low on the body toward the back just above the back braces"? [/QUOTE]

Clarifying my question... If the lower bout CF rod structural members - as in Kent's photo - were not there, it would be obvious that you'd want the tension rod low down as you describe. Otherwise, the tension would pull the top of the butt block in and add to the bellying of the lower bout. But with those rods, it's not so clear to me where on the butt block would be the best place to anchor the tension rod.

_________________
Todd Rose
Ithaca, NY

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

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

You anchor the tension rod in the place that has the most tension...as low in the neck block as possible.   The top of the block is in compression, the bottom in tension. With the buttresses, the virtual pivot point moves up to the ends of the buttresses, but that builds more tension on the bottom (back side) of the block.   Tension/compression=see-saw. &n bsp; Lock it up...