Spanish Heel and Truss rod

Construction and repair of Classical Guitar and related instruments
Rau Le Creuset
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Spanish Heel and Truss rod

Post by Rau Le Creuset » Sat Aug 26, 2017 9:58 pm

I have been reading about the spanish slipper heel method of construction, and forgive my ignorance, but I don't entirely understand the neck problems that can come about because of its design. Are these problems that could be dealt with using a truss rod? Or is it a more deep seeded issue?
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HNLim
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Re: Spanish Heel and Truss rod

Post by HNLim » Sat Aug 26, 2017 10:25 pm

Rau Le Creuset wrote:
Sat Aug 26, 2017 9:58 pm
I have been reading about the spanish slipper heel method of construction, and forgive my ignorance, but I don't entirely understand the neck problems that can come about because of its design. Are these problems that could be dealt with using a truss rod? Or is it a more deep seeded issue?
In my understanding as a woodworker and as a small time amateur guitar maker, neck problem will not occur if you use a properly seasoned straight grained quarter sawn wood for the neck with the Spanish heelblock. Most guitar maker will include a carbon fibre rod or a hardwood strip in the middle like rosewood or ebony. Before the invention of carbon fibre, the other common neck reinforcement material is aluminium. The neck of a properly constructed classical guitar can easily take the tension imposed on it by the nylon strings. There should be this slight bending of the neck which acts as a relieve for the vibrating strings when the strings are on tension.

Alan Carruth
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Re: Spanish Heel and Truss rod

Post by Alan Carruth » Sat Aug 26, 2017 10:28 pm

The issue is not so much with the neck as it is with the body.

A truss rod is good for adjusting the amount of bow in the neck if that distorts over time due to string pressure. Classical guitars have lower tension than steel strings, and a wider and shorter neck, so there tends to be less movement in the neck itself, even if it's made of softer wood, as it often is. Usually the neck relief doesn't change enough to cause fatal problems on a Classical guitar.

On the other hand, the body on a Classical is often more lightly built than on a steel string, and in particular, the top tends to be both thinner and more lightly braced. This means that the body itself distorts over time, even with the reduced string pressure. The action rises, requiring either lowering the bridge or some change in the neck geometry. On a guitar with a detachable neck you can remove it, trim the neck heel to adjust the angle (or in the case of a Taylor NT neck, swap out the shims) and put it back on. For the most part this is not possible with guitars that were made on a solera, since the neck and neck block are one piece of wood.

Traditionally Classical guitar makers and repair people have used a couple of work- arounds for this. One is to use an especially thick fingerboard, which can be dressed down at the nut end to adjust the action height. This is generally a one-time adjustment, but with any luck that's all you'll need. It's not uncommon to plane the fingerboard away to some extent and laminate a new one on top of it to get the correct neck action height.

If the guitar was built with hot hide glue it may be possible to 'slip the heel'. The back binding is stripped back on the upper bout, and the glue line between the back and the heel is opened up, continuing around to part of the upper bout. The neck is pulled back a bit and the heel and bout reglued, after which the binding rabbet is re-cut and the binding put back. I've never done this repair myself.

On really cheap guitars, where the main consideration is to make it playable, a thin saw cut can be made between the heel and the side up to the fingerboard, and a strap button installed using a long screw. This pulls the neck back and gets a few more years use out of the box at minimal cost. You don't do this on a Hauser, Fleta or Freidrich.

The key thing to remember is that the truss rod is not primarily there as an action adjustor; it's function is to control the relief of the fingerboard over the neck. This does, of course, change the action and bit. However, even on steel string guitars the main thing that causes action problems is distortion of the body over time, and the proper fix for that is to reset the neck. The traditional method of building on a solera precludes a simple reset and limits the amount of adjustment that can be made without major surgery.

Rau Le Creuset
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Re: Spanish Heel and Truss rod

Post by Rau Le Creuset » Sat Aug 26, 2017 11:14 pm

I see! Thak you very much for the detailed answer, Alan. So if it is distortion of the body, and the truss rod can only go so far, it seems better to stay away from the spanish heel construction method. Especially if you are a worrisome individual.

Strange then that some companies advertise it seemingly as a plus.

Would the warping body not cause intonation problems? Even with the fixing of the fingerboard height? It is a little confusing for me.

Do many luthiers here use the dovetail where the neck is glued ontop of the body?
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MessyTendon
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Re: Spanish Heel and Truss rod

Post by MessyTendon » Sun Aug 27, 2017 6:25 am

Some do use a dovetail. Truss rod's are not necessary if the neck is thick enough and has support wood or carbon added. The main advantage of the truss rod is that it allows small adjustments to the relief of the neck. It's a really personal feel, there is only so much a truss can do.

It does change the action somewhat, but that is not the purpose. One thing that a truss rod can do on a classical is add weight to the neck. In some cases it can be minimal, but I do think on inexpensive import guitars with truss rods, they are heavy and way overbuilt.

I can tell you there are times when I wish I could just turn a truss rod to make adjustments. A spanish heel neck does change the relief from time to time with humidity changes...it's perceptible but not huge. Still it would be nice to have the luxury of making a seasonal tweak.

As guitars get later in age, they can benefit from fretboard planing and new frets, if there is enough wood to take off then a new fingerboard is often the solution.

In a classical guitar the Spanish heel is a practical and very stable neck for the duration of ownership, that would be you...So I wouldn't worry too much. If you do feel like you would like to have the option to adjust relief every so often, then it's a good option to add if you have a builder make you a personal guitar.

Purists won't like the truss rod. But it's not a bad thing. If you want to see forward progress on neck ergonomics look at Matsuda guitars :)

Recessed, bolt on, elevated disconnected entirely from the soundboard :)

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Re: Spanish Heel and Truss rod

Post by vesa » Sun Aug 27, 2017 6:58 am

Rau Le Creuset wrote: it seems better to stay away from the spanish heel construction method.
Quite a many of the master guitars you have to exclude then as it is the most common way to join the body to the neck(luthier made guitars). Of course everything if badly made can fall in the pieces but don't let bad workmanship overshadow a good construction.
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Alan Carruth
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Re: Spanish Heel and Truss rod

Post by Alan Carruth » Sun Aug 27, 2017 10:34 pm

Some folks feel that the Spanish heel is actually a fairly recent tradition. Most necked instruments through history have used a detachable neck of some sort. Stradivari, for example, followed a common design and butted the neck to the body, making it fast with glue and a nail or two. Later violin makers used a full pocket mortise to hold the neck with no nail. The Spanish method of building the guitar around the neck on a fixture that held the top and neck in alignment may have come about as the guitar system in Spain failed during the long political and economic eclipse after the 17th century.

The solera enables a sort of hand-tool 'mass production', since the craftsman can have several instruments going at the same time on different fixtures, working on one while the glue is drying on others. I know from my own experience teaching that plugging in the neck and getting the fit and alignment right is the hardest and most time consuming part of the job for beginners, and is still fussy even for experienced makers. The solera saves a lot of time in that step.

Longevity in guitars has not seemed to be a major consideration until fairly recently. Historically the guitar has gone in and out of fashion, and undergone changes in size, shape, and stringing fairly often. Unlike the violin 350 year old guitars are not normally used in performance, and there has not been much importance attached to having one by a 'old master' for much of history. Generally through history, a guitar that was more than a couple of generations old was not usable for 'contemporary' music, and could not easily be upgraded, as was the case for violins. People got a new one, and the old one moldered away on a shelf someplace. Why bother to make something that can be played in a hundred years when it's unlikely that anybody will want to?

All of that may be changing. Even as new designs are constantly being tried out many modern makers are also thinking about making guitars that can hold up for many years. Repair people, too, are working out way to keep them playable for longer.

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Trevor Gore
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Re: Spanish Heel and Truss rod

Post by Trevor Gore » Mon Aug 28, 2017 2:34 am

As Alan has pointed out, the Spanish method of construction seems to have evolved primarily for ease of construction rather than ease of maintenance, and guitars do need maintenance over time. I would say the majority of "collectible" guitars I have seen have had way too much relief, which messes with the intonation and makes the guitar uncomfortable to play. A solution of sorts is to lower the saddle, which can result in fretting out on the high frets. And then there are those I see that have backbow, because of the reactance of the ebony fretboard, which, with a raise in humidity can force a backward bend in the neck. This renders the guitar unplayable, temporarily at least. For a novice builder, sanding relief into a neck, then fretting it and experiencing some degree of backward bowing (which may result in negative relief) then hoping that string tension will pull this out, makes setting relief pure guesswork. Far better to engineer a solution so that when the guitar emerges from the climate controlled build environment, it can be set up optimally for whatever climate it's going to spend the rest of its life in, even when that climate changes.

I've been using bolt on necks and truss rods on classical guitars for a long time with absolutely no ill effects. To those who say it adds too much mass, I ask why do you insist on a high density ebony fretboard then?

A bolt on neck for a classical guitar, with adjustable truss rod below:

DSCF8508 - Copy_PS_16_s.jpg

For those who would like to adjust the neck angle "on the fly", there is always the tilt-neck solution (with adjustable truss rod, too).

DSCF9482s.jpg
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Rau Le Creuset
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Re: Spanish Heel and Truss rod

Post by Rau Le Creuset » Mon Aug 28, 2017 11:09 pm

It makes sense that historically the instrument has been built to preform rather than endure. Unfortunately I, and many others, seem to grow sentimental towards instruments. It becomes a partner rather than a tool. A part of your musical identity. Knowing full well that a spanish heel could last entire lifetime (my bad luck aside), I would still rather have the mental comfort of an alternative joint.

Still, I'm not sure how much mental comfort is worth to others let alone myself in full. Is it worth a heavier built guitar? Probably not, but I feel like it must be an important selling point for a few players.

Thank you again, Alan. I'm a history student so I do love reading these detailed responses.

As messy says, a lot of this goes against tradition. Tradition is something I do like to respect. Especially since the Matsuda guitars he so graciously introduced me to revolted me in an odd way. Hidden things like the truss rod don't bother me so. Especially when Trevor gave so many reasons to have one. It creates an odd internal struggle. For some reason the bolt on neck also makes me feel uneasy. Innovation can only go so far for me. As long as it lay under the skin. Perhaps I'm shallow.
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Re: Spanish Heel and Truss rod

Post by Rau Le Creuset » Sun Sep 03, 2017 4:46 pm

I've been looking at production compnies that use the spanish heel method, for example cordoba. Are these guitars built heavier than the guitars built by luthiers? Would that make the spanish slipper more reliable?
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Re: Spanish Heel and Truss rod

Post by Alan Carruth » Sun Sep 03, 2017 8:43 pm

The Spanish heel construction, with the sides plugged into the neck, is a separate thing from the slipper foot inside. It's perfectly possible to make a plug in neck with a slipper foot. The slipper foot is thought to stabilize the neck a bit. It's hard to say whether it does or not. It is an expected feature of Classical guitars, though, so woe be unto him who makes one without it.

Obviously, when the sides are plugged into the neck it's impossible for the neck to get loose, as can happen on a plugged in neck if the joint is not carefully cut and glued, or (these days) well bolted down. In that sense it's 'more reliable'. On the other hand, action problems are not usually the fault of the neck pulling loose, but rather have to do with distortion of the box. When that happens you have to be able to adjust the angle of the neck relative to the side, and that's not possible when the sides are plugged into slots on a sold neck. 'More reliable' in this case works out to 'less repairable', or, at least, less easily repairable.

SteveL123
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Re: Spanish Heel and Truss rod

Post by SteveL123 » Sun Sep 03, 2017 8:59 pm

Would an adjustable neck like Smallman solve the problem of distortion of the box? Which is more work to build? Traditional Spanish neck, bolted, adjustable? Are there tonal difference between them?

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Trevor Gore
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Re: Spanish Heel and Truss rod

Post by Trevor Gore » Sun Sep 03, 2017 11:23 pm

SteveL123 wrote:
Sun Sep 03, 2017 8:59 pm
Would an adjustable neck like Smallman solve the problem of distortion of the box?
It won't stop the box distorting, because the torque on the neck still has to be reacted by the box. However, adjusting to compensate is a lot easier.
SteveL123 wrote:
Sun Sep 03, 2017 8:59 pm
Which is more work to build?
I do bolt-on necks and tilt necks (adjustable necks) as per the pics above. I don't know what the Smallman joint is like (never seen inside one), but most tilt necks are permutations on the Stauffer style adjustable neck. The woodwork is obviously different, but once tooled up there's not much in it either way. For a bolt-on neck you're adjusting angles and fits precisely; for a tilt neck you're adjusting more fits precisely. E.g. too much finish on the sides of the neck where it lets into the guitar top means it won't move!
SteveL123 wrote:
Sun Sep 03, 2017 8:59 pm
Are there tonal difference between them?
Not that I (or anyone else I know) can hear on my guitars.
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Re: Spanish Heel and Truss rod

Post by SteveL123 » Mon Sep 04, 2017 1:29 am

"It won't stop the box distorting, because the torque on the neck still has to be reacted by the box. However, adjusting to compensate is a lot easier"

Yes, the top will keep distorting with age and string tension, but the adjustable neck can compensate by turning a set screw instead of requiring a neck reset on a Spanish neck. Isn't that in effect solving the problem of box distortion?

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Re: Spanish Heel and Truss rod

Post by SteveL123 » Tue Sep 05, 2017 3:10 pm

I really like the idea of a bolt on neck and adjustable necks like the Smallmans. What is the clearance between the neck and body joint in such designs? Is there any worry of unequal expansion from humidity changes resulting in damage at the body joint. For example, if the removable neck's heel expands at a higher rate than the body joint, is there a possibility of cracking the body?

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