Official Luthiers Forum!

Indeed great thread. I like it when fundamentals are questioned!



I think that's the key right there. In a nut sheel, if a guitar never needs a neck reset, chances are it's overbuild. Of course there are builders that claim they have a 'neck reset proof' design. I believe Howard Klepper who uses carbon fiber rods to reinforce the neck joint area never needed to do a neck reset on one of his guitars. I'm not sure but I think Alan Carruth who uses an 'A' brace design in the neck joint area of the soundboard also never had to do a neck reset on one of his guitars. Now I don't know how long they have been using these designs. Chances are it's less than 30 years, so it's hard the say there are full proof designs. (Howard and Alan, correct me if I'm wrong, of course...)



Talking about that, I never fully understood why this (bellying and caving in around the bridge) is such a bad thing. Of course I had to repair guitars that bellied so much that the bridge gave away. But I also played several guitars that bellied and caved in without problems; the action was good and the sound too.

So I wonder what others think about that too...

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Alain Moisan
Former full time builder of Acoustics, Classicals and Flamencos.
(Now building just for fun!)

As has been said, when you put string tension on a guitar, if it's made of wood, it's shape is going to slowly distort over the years. Wood does that. No way around it.

You can make a neck that can be kept straight (with or without a bit of relief). You can construct a box with extremely rigid back and sides; or a rigid internal structure that maintains the geometry of the back and sides, including the position of the neck block (a strategy that makes good sense to me). But the top is still going to distort. The torque and pull on the bridge is going to change the shape of the top. If the top is made to be acoustically responsive, it will change shape some the first time it's strung up - the whole bridge lifts a smidge, the area behind the bridge bellies out a bit, and the area in front of the bridge sinks a bit; if that doesn't happen at least a little, you're going to need a pickup and an amplifier to get much sound out of that guitar. And that distortion of shape will progress over time, because that's what wood does.

So, from that alone, at some point the neck angle is going to have to be adjusted to keep the action where it should be. That can be a turn of a bolt on a guitar with an adjustable neck joint, a relatively quick and painless reset on a bolt-on neck, or fairly major and expensive surgery on a dovetail joint. To me, a neck joint that can be easily adjusted, including bolt-ons that make a reset easy, is the most fundamental way of making a guitar serviceable. However, if it's a good guitar with a dovetail neck joint, it's well worth doing the reset to keep it alive and playing.

The thing that gets my goat is that the vast majority of guitars manufactured are essentially disposable pieces of garbage. That is, the neck joint cannot be easily adjusted/reset, and the guitar isn't worth the cost of a dovetail reset, so nobody's ever going to do it. The day it's made, it's bound for the landfill, as soon as it needs a reset - or a refret, or just about anything else. I know I'm treading dangerously close to getting "political" here, but the amount of disposable, landfill-bound junk in our society is sickening in the extreme; the fact that we've turned musical instruments into such junk really makes me want to puke.

Nothing lasts forever. That's true. But I do think a guitar should be made to last at least a hundred years, or it shouldn't be made at all. And it WILL need repair, adjustment, refretting, etc, in its lifetime.

End of rant.

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Todd Rose
Ithaca, NY

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

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

Thus the ability to change the action without re-tuning. By moving the neck up and down in a linear fashion in the block, rather than changing the neck angle with respect to the block, the string length doesn't change as it would if the neck angle were to change. In reality though, there is a change of string length with Babicz's linear motion, but it's very small at the range of travel for this situation. Imagine if the neck moved a foot, there would be a change, so if a foot brings about a change of string length, surely moving the neck 1/32" would also bring a change in the string length, but on the order of thousandths of an inch. The only way one could truly keep the string length from changing would be to move the nut end of the neck in an arc with the saddle as the center of the arc. There are ways to do that, false center or something like that, but it would be really bulky and heavy. But I think we're (I'm?) splitting split hairs here.

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formerly known around here as burbank
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http://www.patfosterguitars.com

Hesh wrote:
" 145 degrees will release HHG and fish glue should a bridge ever need to be removed or replaced."

Hide glue will NOT release at 145 degrees without some water. Iirc, Frank Ford did an experiment where he glued up blocks of wood with hide glue and Titebond, and put them in the oven. The Titebond let go at about 145, but the hide glue held on long after the wood had started to char.

Wood 'cold creeps'. The lignin glue that holds the fibers together is a 'thermoplastic', and, as is common with such things, it will flow when subjected to any force at all. The effect seems to show up mostly in shear loading, when the cells of the wood slide past each other. We use this to our advantage when we bend sides, but it works against us when, as Don said, the guitar tries to swallow itself through its own soundhole. So long as you're using wood as your main structural material, you'll have some degree of this.

I haven't seen those old guitars you're talking about, but I'd bet they have moved a little bit. As has been pointed out, if they're relatively heavily built they could remain playable for a long time without a neck reset. Note I said 'relatively'; small spans can hold up very well over time, even with light construction.

Are there ways around the problem? Certainly. Wood in direct compression doesn't seem to move much, if at all, so the use of things like A-braces on the upper bout that inlet into the neck end can be a big help. Some folks have used 'flying braces' to link the upper block with the sides at the waist, and claim that adds a lot of stability. You can go the 'piano' route: using a steel/iron/CF/whatever frame to take up the string tension, and the whole stability problem goes away. Weight, on the other hand.....

Epoxy is not a cure-all. For one thing, many epoxies do creep. For another, they may not have higher peel resistance than the hide glue or Titebond that most bridges are glued on with. So far I have not come up with a way to remove epoxy that does not damage the wood, and as long as there's _any_ chance the the bridge might come up, I'd opt for a reversable glue. HHG is by far the easiest to reverse, and seems to be about as strong as anything I've tried.

I believe, at least the majority of neck sets I have had to do on fairly new guitars (not on my guitars but on repair work) excluding one wher the neck was just plain set poorly, is caused by the sinking of the fretboard extension at the sound hole combined with the neck block and rim to tilting inward at the top. The normal culprit of string tension is of course part of the cause and the main instigator but almost every reset I have had to do on a near new (0-5 year old) guitar the neck block was thinner than I like to build to and the UT brace was too thin. Environmental conditions can and will cause the wood to move in time. Depending on how built maybe enough to case the need for a neck change. The Idea that all necks will need reset at some point is based on conventional building techniques. It is possible with construction methods to at least put off the en enviable for quite a long time. But Like Done said Wood moves.

A little correction,

In Frank Ford's experiment, the hide glue and Tite-bond did let go at about the same temp, but only when both were under quite a bit of stress. Without stress, the hide glue held at 375°F.

That's what enabled me to remove my bridge plate glued with hide glue without having to use water, heating the bridge plate with a dry-mount tacking iron.

Pat

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formerly known around here as burbank
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http://www.patfosterguitars.com

Burton, I haven't glued a fingerboard to the top for the last 20 or so guitars I have built. The earliest guitars of mine that were built like this are still in perfect shape after ten years of use, but you do have to change the headblock to take account of this. My headblock is three pieces which include a Spanish heel and a similar extension into the top. The neck itself has an extension to which the fingerboard is glued and which fits a pocket routed into the neck block extension. It has been illustrated a number of times over the years here, and even received Rick Turner's blessing as a solution!

Colin

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I don't believe in anything, I simply make use of a set of reasonable working hypotheses.

Well I have to say that it does my heart some good to see so many responses to my query, makes me think others have thought this too, but just never wanted to bring it up for fear of newbie strikes and stirring of bees. I admit I am not well versed in the school of lutherie teachings, traditions and held true
doctrines of proper (conventional) methods of construction, or for that matter time tried and tested instruments of my own. But it doesn't stop me from questioning why certain techniques are used to establish the generally accepted fabrication of a high end top quality acoustic guitar. I see errors in some of these.
I'll explain a little---the upper bout of a guitar can be used (if properly placed and thought out) to re-inforce certain structural elements pertaining to the longevity and endurance of wood versus tension.
This is something I've been working on in my mind and shop. The transverse bracing techniques used in conjunction with most back plates inhibits lateral flex and movement along the grain, the back's primary function is to remain a "sounding board" for frequencies and vibrations caused by- string under tension- energy transmitted in, out and through the guitar. It is my personal opinion that a back can be made as stiff as possible, and the resulting tone will only increase. We know this true by, using a soft pliable back eminates a duller sounding of notes.
Now if the back plates were to be braced 90 degrees to the (common) bracing and tied in to the neck block along the structural grain of the back plates, thus strengthening the core of the body, the resonant affect from the ribs and back are now unified in the transference of vibrating energy, the top , while anchored with pins and holes in the center of it's resonating field, is compromised by focusing strain and tension on the weakest link of guitar construction, pass over this "field" or drum skin and tie the tension in to the body of the instrument at the second strongest part, the bout. (This is why I use tail-pieces even on flat tops), and now you have created an instrument that can withstand abnormal tensions and still , actually even more so, move with the vibrations caused by string in pitch tensions. I've heard some builders discount this setup as it puts too much downward force on the top, not so! A simple adjustment to bracing mass is all that is needed to compensate in the bridge area.
If an instrument is wanting to cave in at the bridge it makes perfect sense to me that this is not the optimal location to rely on lateral string tension.
Beefing up the bracing or structure under the saddle only kills the sound, the sensible compromise in this system is too allow for bellying and repair later, while maintaining temporary resistance to tension. This is fine and undoubtedly necessary for most designs. I am working on a concept guitar with very different bracing patterns and even adhesives in its assembly to test my theories about placing string load on fragile tops, while decreasing the need to have the neck reset or bridge replaced.
I hope that my comments have not offended anyone here or caused a need to rip me as I like to discuss fundamentals and such.

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Nehemiah Covey
www.coveysacoustics.com

Colin,

My neckblock is actually very similar to yours. You wrote once that the neck block is the first thing to be made and thought of as the guitar is built around it. (at least I remember it as you, please correct me if I am wrong). I took inspiration from that. Maybe it is a matter of degree? My upper and lower extensions are not as thick and don't extend all the way to the UTB or LTB. I usually extend wood and CF through the neck block glued to the FB at least 2 inches into the upper bout and even with wood and (2) 1/4x3/8 CF bars I am getting some distortion. None of the guitars have needed a neck reset but all of them have without the extension locked in developed the ski ramp right at the join and the upper bout of the top has remained flat. Usually this happens after a Northeastern summer and does not fully go away again. I am inspired that yours are working, that means it can work! A few questions of you don't mind:

-Are they all really flat through the join or is there an acceptable amount of creasing?

-Do the top and back paddle extend all the way to the upper transverse braces of the top and back?

-What is the radius of the back dome and is it compound or continuous(dished) and how beefy is the upper bout brace on the back?

-How thick are your sides at the upper bout and what kind of linings have you been using?

Thanks!

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

I think glue creep is part of the problem , maybe it wont creep under normal conditions, but a guitar left in the warm sun , or the trunk of a car( or back seat), or a little too close to the heating register in your home, or left in a closet of an older home,on a wall that gets sunlight . if we release the glue at 150 degrees, it only makes sense it will begin to soften before that tmperature. Jody

This is a great thread, and I have pondered these issues, too. I must say at the outset that I am not an engineer nor an acoustic scientist--just a hobby builder. After reading the whole thread, my thoughts have drifted towards the phenomenon of top deflection. I know why the traditional bracing solutions are used by most builders (with a little experimentation here and there). It's because they WORK. Further, I understand that most professional builders don't have a great deal of time for radical experimentation. Their clients expect things to sound a certain way and to play a certain way, and to remain basically problem-free for a certain period of time. But my thoughts go back often to radical solutions to bracing problems. I think most of these radical solutions must have been tried at one time or another by a hobby builder, or by a pro who has time and resources to experiment. Gradually, some experimental solutions to various bracing problems have found their way into an expanded building community. Some examples: Carbon fiber reinforcement in necks and top braces. Bill Moll is noted for his thin but deep archtop x-brace, which is scalloped to remove weight and mass. Immensely strong, but with a narrower footprint than the traditional x-brace. James D'Aquisto was also a noted experimenter in the later part of his career. We now have various flying buttress designs to reinforce neck blocks, etc. I'm purely dreaming here, folks--I have very, very little experience actually building these instruments. But I keep wondering about things such as
a very narrow but massively tall transverse brace in the upper bout, under the fingerboard extension--replacing the popsicle stick and the conventional wide brace. What if it were made out of radically new material, giving massive strength with a very small footprint? Would the resulting tone sound like carbon fiber? or aircraft aluminum? or some material that hasn't even been invented yet? What about a honeycomb bracing system in that area? What about a truss assembly--somewhat like a scaled-down garage rafter system? What about a top that was thicknessed to resemble a wedge (fairly thick between the sound hole and the neck block, but traditionally thin below the sound hole)? Surely, all of these ideas have been pondered by someone else. Perhaps tried by a few. Obviously, none of them have become commonplace in our contemporary guitars. Is it because they've been tried and they didn't work? Or is it because they are expensive experiments in terms of time and materials, and most pros just don't have the time to spare on them? I'm not trying to stir up a hornets' nest here--only relating some random thoughts that I've had.
Often, traditions are kept alive because they work so well. But sometimes, traditions are kept simply because things have ALWAYS been done in that way--and that alone is not a good enough reason to keep them.

Best regards to all. Most of you have forgotten more about guitar building than I will ever know in my life, and I respect you for your knowledge and skill.

That's a whole can of worms there and perhaps "I believe this true" rather than "We know this true" would have been a better phrasing. If "stiffest possible backs" are the way to go then perhaps we should seek out the space age material (I'm sure the engineering builders here will know some) that is light in weight and has similar properties to sheet steel or the like and use that on a back - that certainly won't be moving anywhere in a hurry.

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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

To answer the specific questions, yes they are really flat, taking the neck off and on there is no difference, no crease whatsoever.

The top neck block extension goes to within about 5mm of the UTB, the back Spanish heel a little further away, they are both 80mm x 80mm usually, with the top one being 18-20mm thick and the Spanish heel about 12-15mm.

Back radius is the usual 15" dished

My sides are the usual 2mm or so according to the bending characteristics of the wood used, and I use solid 4-ply laminated linings now though when I used reverse kerf linings the results were the same, though I do prefer the laminates now.

How do you make the necks? It is important that the extension of the neck is a continuous part of the neck wood with the fingerboard glued to the same wood all the way down. here's a very brief photo set on how mine go together.





I then glue up the heel stack and cut the face to 1.5deg before gluing it to the neck shaft. Then just band saw to shape.



I use the router template for the top mortice to establish the mounting hole position and mark the neck heel for the inserts by a punch from inside the body.



Colin

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I don't believe in anything, I simply make use of a set of reasonable working hypotheses.

The stiffer the plate, the higher its main resonant frequency will be, all other things being equal. Some studies of guitars and other instruments have demonstrated that if the main back resonant frequency is about a semitone higher than that of the main top, the instrument has the most power, along with other positive qualities of sound. Al C. is our resident expert on that.

On the other hand, there may be qualities of sound that a stiff-as-possible back gives that are appealing as well.

Lots of guitars have been made with designs based on ideas similar to yours. Checking out those guitars and the sound they make would be my first stop on a journey of exploring those ideas. A contemporary example is Batson guitars.

Personally, I like the sound of pinned bridge guitars, and I don't really see the resulting stress on the top as a "problem". It's just a fact of that design, to be dealt with appropriately.

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Todd Rose
Ithaca, NY

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

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

I like your solution to the problem at large, Colin, thank you for being so informative about it. A Spanish Heel is something I would like to try with the next build. Although I use a bolt-on neck, I would have to make the Spanish Heel a little thicker.

Back to one of the original questions . I think some of the possible reasons guitars need neck resets might be due to , finger board glue creep ( sorry Chuck) , too flexible neck wood/design .undersupported ( or weak wood used for the ) transverse brace area . forward shifting neck block,( i personaly doubt if rod buttressing will work , for several reasons, we will know if I am wrong in a few years ) too thin and/or underbraced ( or poorly designed braced)tops, and the use of strings too heavy for the design of the instrument . I think most of these issues have solutions ......... fire away LOL Jody

Just to throw some more fuel on the fire-One of the other patents the Jeff Babicz holds is for the "lateral compression sounboard. The tension is completely different than a "standard "guitar so the bracing can be much lighter.

The sound is also "completely different", IMO.

There are probably a million ways to make a "better" guitar, not all of them will necessarily make a better sounding guitar, at least if your reference for good guitar sound is formed by instruments already in existence.

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Rian Gitar og Mandolin

Thank you very much for your answer Colin.

I do see a few things differently than what I am doing but it is still very similar. Your CF bars are splayed out wider than mine and I do not have that much wood extending into the guitar body. That would probably be the kicker there along with the thicker paddle underneath. I appreciate you taking the time to give a detailed and photo-rich answer, it gives me a lot more to think about.

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

They sound" great to me, although "sound" is completely subjective!

So far the only guitars i've tested that had totally 'reflective' backs were Ovations. Now you know what that sounds like. And, BTW, I can attest that putting on a better top doesn't change the basic sound all that much.

And, of course, the lute Alan. It's part of what gives it the clear focused sound, and a sound very different from what we normally think of as that of the guitar.

Colin

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I don't believe in anything, I simply make use of a set of reasonable working hypotheses.

I didn't read all the corresponding replies to my question as it seemed it was going off topic, but I have to clarify ( really cool set up you've got going there , Colin) that I am not suggesting that a back be made as stiff as carbon fiber or sheet steel, but within reasonable stiffness for a back of appropriate woods. That's what my interpretation of my post reads to me anyway. Sorry if it implied otherwise.
And Todd Rose, I'd love to sample other tail-piece equipped guitars, but very few make them and none are available for me to compare. So I just make my own and , hey, if you would like to try it for yourself, let me know, as soon as I get another one done I'll send it for evaluation, I really need that actually. I am sort of tucked away out here in the wheat-fields and have few chances to share and compare

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Nehemiah Covey
www.coveysacoustics.com

Nehemiah, I understand the challenge of getting one's hands on a lot of the guitars one would like to hear! I'm pretty isolated here, too, as far as having access to a wide variety of guitars. I take advantage of every chance I get, though.

I would be delighted to have you send me one of your guitars for evaluation. That would be totally cool. By all means, let's keep in touch about that.

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Todd Rose
Ithaca, NY

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

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

I think you hit the nail right on the head Ken! You could drive a tank,and it will last for ever,but isn't a corvette much more fun to drive? I'd rather replace a guitar more often to have great tone, than to play a tank for the rest of my life that sounded bad. Anyone agree?