Guitars prone to Neck resets and bellied up bridges

[HNS]

What guitars are more prone to body warps, neck resets and bellied up bridges?

*Would a short scale be less prone than a longer scale? Would the placement of the bridge make a difference on a 12 fretter ?

*Does body size have an impact, are OM or grand concerts less prone than dreads, due to the size of the top?

*Would lighter strings help in this regard? It should.

*Does bracing and design have an impact?. It’s reported that the heavily and symmetrically braced larrivee guitars for instance are less prone to neck resets and body warps.

*Top wood stiffness must have an impact, it would be counterintuitive if it it didn’t.

*Does the neck have any kind of impact?

*Are bolt on necks substantially easier to adjust in the event of a neck reset than dovetails or is it just a marginal issue?

I was considering the new 900 and 800 Taylor series and it seems that the diagonal back brace, according to some reports, has made the guitar’s back a bit wobbly. Would that be prone to body warps down the line? It would be weird if it did.

I was searching the net for some kind of theoretical model to put the issue in perspective and was hoping that the professionals and luthiers in the forum would chime in. I’m sure I’m not alone in hoping to put this issue in its right framework.

Cheers

HNS

[charles Tauber]

That's a lot of questions.

The bottom line is that it is the manufacturer's job to make a guitar that remains in playable condition "long enough". The primary thing for a consumer is to ensure that the manufacturer's warranty covers a neck reset should the guitar eventually need one.

These days, it seems there are a number of new guitars that come out of the factory with neck angles that are marginal or with incorrect neck angles. A buyer should check that on any guitar purchase - new or used.

There are many factors that go on "under the hood". Consumers trying to second guess a causal relationship between those factors and the need for neck resets or excessive bellying doesn't make a lot of sense. Guitars are a balance between structure and responsiveness: too stiff/massive a structure and the guitar lasts a long time, but at the expense of responsiveness; too little stiffness and the guitar might be very responsive, but prone to structural problems in short order. Many manufacturers build on the too stiff/massive side to reduce warranty work. What many players are after is that slim middle-ground where both responsiveness and longevity are optimized. That optimization doesn't depend on a single variable, but on many, some of which you've mentioned.

To attempt to address your questions more specifically, the guitar design that first comes to my mind are many 12 string guitars. The added tension often results in top bellying and the need for a neck reset.

Scale length, by itself, doesn't make much difference, in the common scale lengths used by makers. Ditto for placement of the bridge, in and of itself.

Less tension reduces bellying and might forestall the need for a neck reset. That can be achieved by lighter gauge strings, tuning down (e.g. 12 strings), lower tension strings (e.g. silk and steel) and, if not playing the guitar for an extended period of time (e.g. storage), remove string tension.

Of course bracing influences top bellying and the need for a neck reset. Some use carbon rods between the sides and the neck block to resist movement of the upper bout; others use "A frame" bracing in the upper bout. Larrivee does seem to have success with its cross brace below the bridge plate to reduce bellying of the top. (I tried it once on a guitar I made and didn't care for the result.)

Top stiffness seems like it would be a factor, but probably less than you might think. Bracing dimensions and placement are likely a greater factor, as is the size and placement of the bridge plate. The bridge is the largest brace in the middle of the top: bridge design likely has some influence as well. (Think very narrow, rectangular bridge vs. wider bridge; tall vs thin; wing design.)

As long as the neck is stiff enough to resist string tension, it its common configurations, it isn't a factor in neck resets or top bellying.

There are different "bolt-on" designs. Some still have the fingerboard extension glued to the top, making a neck reset somewhat more difficult. Some bolt-on designs have an integral fingerboard extension, some allowing the neck angle to be changed just by adjusting a screw. Certainly these are easier than releasing a glued-in dovetail joint with a glued-down fingerboard extension. At this point, it seems to me, that the only reason to use a dovetail joint is tradition.

I don't know what is meant by making the back "a bit wobbly". The top, back and sides work as a unit to resist the pull of the strings. A neck reset, most often, is needed because the entire unit deforms - back, sides and top. What one does with back bracing is just one of many factors that go into the structure of that unit.

The "framework" is very simple: string tension attempts to fold the guitar "into the soundhole". As it does so, the upper bout "curls", the top sinks between the soundhole and the bridge and rises between the bridge and the butt, forming an "S" curve, the sides bend on edge and the back increases its curvature along its length. The structure of the guitar body - including top, back, sides, linings, braces, neck block, bridge plate, bridge, fingerboard extension - needs to be designed so that it resists the slow deformation of its geometry, the deformation of which is "countered" by changing the neck angle. (It has little to do with the neck itself.) There are many elements that go into creating this structure.

Makers have tried many combinations and permutations to find what works "best", giving an optimization between structure and responsiveness. These include everything from the use of composite materials, the use of carbon fiber reinforced bracing, all manner of bracing arrangements - X, A, fan, lattice, ladder - double tops, double sides, solid linings, "reverse" kerfed linings, "L" shaped neck blocks, "U" shaped neck blocks, rectangular neck blocks, and so on and so on.

Rather than try to wade through all of those combination and permutations to find what is "best" in terms of neck reset and top bellying, to repeat, the best "defence" the consumer has is to check the neck angle on any new purchase, look for any excessive top bellying and ensure that neck resets are covered under the manufacturer's warranty.

[HNS]

Charles Tauber
Thank you very much for the quick detailed response and good advice.

I guess Martin stopped extending warranty coverage to neck resets. I don't know about the other manufacturers, but I need to look into it. Unfortunately, some guitar manufacturers don't honor their warranties outside the US. A bummer for us travelers.

I understand now that the neck angle is of prime and foremost importance. That makes perfect sense, and hence your comment on the more versatile bolt-on necks and the need to have it right from day 1.

I was referring to the Taylor 812/912 new design when I said that the new slanting/diagonal brace on the guitar's back - according to some reports - has made the back wobble a bit. I still have to see it for myself though.

So from what I gather that a guitar is an integrated whole that has to be analyzed in its entirety if we would come up with a model for neck reset need, and that - other things equal (braces) -a smaller top (as in a 0 or 00 or 000) should make structural changes "less likely" on the top over time, similarly a bridge in the middle of the top (farther from the soundhole and the bracing around it) is "more likely" to belly as well.

I would also infer that a belly bridge with a larger footprint would be more prone to bellying than a rectangular/pyramid bridge for instance (since it would have less pull on the top). Correct?

* My Larrivee took years to open up. I can relate to your comment on the cross brace below the bridge.

Cheers

HNS

[charles Tauber]

Originally Posted by HNS

I guess Martin stopped extending warranty coverage to neck resets. I don't know about the other manufacturers, but I need to look into it. Unfortunately, some guitar manufacturers don't honor their warranties outside the US.

Context is important. For discussion sake, let's say a neck reset on a traditional dovetailed neck is $600. If you find an instrument that speaks to you and is one that you intend to keep for 30 years, that $600 is $20 per year over your ownership of the guitar. It's nice if the manufacturer covers that, but if not, not the end of the world.

If you only plan on keeping the instrument for 2 or 3 years, then sell it, and the guitar needs a neck reset within those 2 or 3 years, the $600 is significant, particularly on, say, a $1000 guitar. Many, many players these days, buy and sell repeatedly. "Know thyself."

I understand now that the neck angle is of prime and foremost importance.

The neck angle is largely what determines playability. I wouldn't describe it as of prime and foremost importance, but, rather, as a prerequisite for considering the purchase of an instrument. On a new instrument, if the neck angle isn't right, there is no reason to evaluate anything else on that instrument: it's dead in the water. On a used instrument, if the neck angle isn't right, the cost of a neck reset should be factored into the selling/buying price.

I was referring to the Taylor 812/912 new design when I said that the new slanting/diagonal brace on the guitar's back - according to some reports - has made the back wobble a bit

.

I understood that you were referring to the Taylor, but I still have no idea what the back wobbling a bit means - or why it would be of concern to a buyer.

So from what I gather that a guitar is an integrated whole that has to be analyzed in its entirety if we would come up with a model for neck reset need

It is a complex system with many variables, too many variables to faithfully model. One can simplify the system, and many have, to make models, but in doing so, the predictions one makes based upon the response of the model are only as good as the original model.

other things equal (braces) -a smaller top (as in a 0 or 00 or 000) should make structural changes "less likely" on the top over time,

And, that's the catch. Other things aren't equal. A smaller top with the same "amount" of bracing won't sound very good - it will be over-braced. A smaller bodied guitar is braced lighter to retain responsiveness.

similarly a bridge in the middle of the top (farther from the soundhole and the bracing around it) is "more likely" to belly as well.

Again, other things aren't equal. If the bridge moves, the bridge plate moves. If those move, the braces move, or change the included angle, if using an X brace. That's the point: it is an integrated system of inter-related variables.

I would also infer that a belly bridge with a larger footprint would be more prone to bellying than a rectangular/pyramid bridge for instance (since it would have less pull on the top). Correct?

No. If you changed nothing else but the bridge, a belly bridge is wider and therefore stiffer and heavier. The width spreads the forces out over a larger area. If anything, it would reduce bellying, though probably not by an appreciable amount. However, the bridge plate is usually sized relative to the bridge width: a wider bridge gets a wider bridge plate. Many makers pass the legs of the X brace under the ends of the bridge. Changing the width of the bridge, depending on the maker, might also change the angle of the X brace. A wider bridge and wider bridge plate would reduce bellying. (Then there is the well-known manufacturer who, for many years, used spruce for the bridge plate: neither hard enough to resist the string ends, nor stiff enough to provide the necessary structure, nor did they make it wide enough to be effective. Again, additional "variables".)

But, response is proportional to stiffness and mass. Make the bridge plate and bridge too wide, too thick, you increase "structure" but at the expense of response. It's a balancing act. There are many ways to achieve that balance. Hence many variations in the details of how guitars are made.

[HNS]

Got you .... so in essence, we cant really predict neck reset probability at purchase. If it's only a 30-year occurrence then that shouldn't be a problem, what horrors many of us is the need for a neck reset 6-7-8 years after buying new, and it's not uncommon to find such cases.

Thanks again ... you've been a great help

[Truckjohn]

Assuming "Good guitars" - the question is not "If" - it's "When"....

The reason is that they are not designed as Furniture or decoration - but rather as a Musical Instrument.

If we assume Martin as a yardstick - a "Good" guitar will need some significant maintenance/neck reset between 20 and 40 years.

This is inherent in the basic nature of the design. Its not an indication of poor workmanship or poor materials choice..

A "cheap" guitar will most likely require major maintenance and neck set sooner due to shortcuts taken in design for low cost manufacturing or low cost materials...

[HNS]

Originally Posted by Truckjohn

Assuming "Good guitars" - the question is not "If" - it's "When"....

The reason is that they are not designed as Furniture or decoration - but rather as a Musical Instrument.

If we assume Martin as a yardstick - a "Good" guitar will need some significant maintenance/neck reset between 20 and 40 years.

This is inherent in the basic nature of the design. Its not an indication of poor workmanship or poor materials choice..

I understand that.... 20-40 years is good... unfortunately some need resets much earlier.

[charles Tauber]

Originally Posted by HNS

Got you .... so in essence, we cant really predict neck reset probability at purchase.

A new guitar that has the wrong neck angle has a 100% probability of needing a neck reset.

If it's only a 30-year occurrence then that shouldn't be a problem, what horrors many of us is the need for a neck reset 6-7-8 years after buying new, and it's not uncommon to find such cases.

At $75 to reset a Taylor-style bolt-on, it isn't much of an issue, even 6 to 8 years in.

For non-bolt-on's, make sure the neck angle is good when new. If good then, it probably will be fine for 10 or more years, unless it has 12 strings. However, if a $1000 guitar, for example, needs a neck reset at year 8, you can buy a new one and give the old one away: your cost of playing and enjoying that guitar was $125 per year, probably less than most spend on their cell phones per year. While I don't encourage that approach, it does put it in context.

[HNS]

Originally Posted by charles Tauber

At $75 to reset a Taylor-style bolt-on, it isn't much of an issue, even 6 to 8 years in. .

Thank you again for your help... I'm considering the Taylor 812 or 912 ... probably ....

[ChrisN]

Based on your questions and Charles's comprehensive response, the issue is one of trade-offs. You can get a guitar you don't have to worry about putting some money into, but it might be overbuilt and not sound as good as one that is lighter-built, but more vulnerable to stresses over time.

I have and like Taylors. I like the sound, and I like that I can reset the neck easily at no expense and be assured the sound won't change when I'm done. Others care more about tone and don't think about a $300-600 reset cost down the road.

I think most here would say, get the guitar that feels/plays and sounds best to you, and don't worry about getting work done on it.

[Truckjohn]

Yes - Charles makes a very good point... At $75-100 for a neck shim adjustment... Why worry about it? Even if it does belly or the body flexes pematurely - it's cheap to readjust the neck for good playability.

[HNS]

Originally Posted by ChrisN

s. I like the sound, and I like that I can reset the neck easily at no expense and be assured the sound won't change when I'm done. Others care more about tone and don't think about a $300-600 reset cost down the road..

Thanks Chris
TruckJohn

I've had tanks for guitars in the past, but as you pointed out Chris they aren't worth much tone-wise.

The cost isn't my primary concern, it is something to put in mind, but as Charles said in 30 years it's peanuts, especially compared to the guitars that I currently own. I'm not sure I'll be there in 2047 anyway , so who cares what will happen then.

Being a globetrotter, I sometimes find myself in places where I don't find good repairmen/luthiers. That's my main concern.

So an easier job is easier to get done properly. I don't think I can get rid of at least two of my Martins in any event.

[dekutree64]

I'll start off by saying "no to all" (except that bolts are easier to reset than dovetails)

The issue is down primarily to bracing design, and the exact thickness/height you make everything, relative to the Young's modulus of the wood at hand and the string tension you plan to use. Brace material strength also plays a part. The closer wood is pushed to its breaking point, the faster it will take on permanent deformation over time. Spruce has higher strength than western redcedar, and carbon fiber has higher strength than spruce.

Strength is only really a concern for braces, where you have a lot of stress focused onto a small amount of material at the peak. As far as solid materials go, spruce has pretty much the ideal combination of properties. Composites can do better by putting the strong and heavy stuff just where you need it, but it's more work.

My goal with bracing design is to make the upper bout absolutely rigid, soundhole area medium, and bridge area flexible. That way, the action only really rises as a result of the entire lower bout of the box bending upward. And since that's a long distance from the center of the string, it takes a lot more movement to cause a given change in action height than it would take in the upper bout area.

Rim stiffness should also increase stability. And adding mass to the rim improves volume/projection as well, which is why a lot of builders use double sides.

[HNS]

Originally Posted by dekutree64

I'll start off by saying "no to all" (except that bolts are easier to reset than dovetails)

The issue is down primarily to bracing design, and the exact thickness/height you make everything, relative to the Young's modulus of the wood at hand and the string tension you plan to use. Brace material strength also plays a part. The closer wood is pushed to its breaking point, the faster it will take on permanent deformation over time. Spruce has higher strength than western redcedar, and carbon fiber has higher strength than spruce.

Strength is only really a concern for braces, where you have a lot of stress focused onto a small amount of material at the peak. As far as solid materials go, spruce has pretty much the ideal combination of properties. Composites can do better by putting the strong and heavy stuff just where you need it, but it's more work.

My goal with bracing design is to make the upper bout absolutely rigid, soundhole area medium, and bridge area flexible. That way, the action only really rises as a result of the entire lower bout of the box bending upward. And since that's a long distance from the center of the string, it takes a lot more movement to cause a given change in action height than it would take in the upper bout area.

Rim stiffness should also increase stability. And adding mass to the rim improves volume/projection as well, which is why a lot of builders use double sides.

Thanks for your insight.
By composite, do you mean carbon fiber tops? I thought it would be less work. So what I understand is that you have more bracing in the upper bout and it decreases as you go towards the lower bout. I would like to hear it. Any youtube vids?

I thought that the double top was just a synthetic mesh attached to the top. I didn't think it would affect strength that much.

[Truckjohn]

Some builders have started to cap their braces with carbon fiber. There are builders who additionally cap the bridge plate, reinforce the bridge, and even stiffen the rim structure with carbon fiber.

The idea is mainly to reduce cold creep over time... CF does not cold creep like wood does....

There may be trade off's though. Some of the early pioneers of this have mentioned failures of the epoxy/CF sandwich between the brace and the top.. Its apparently not super common (or boats would be failing all over the place - they aren't) ... But it has been reported....