Twelve-string setup

I have a question for you about 12 strings guitar set up.
I do not have much experience in playing and setting up 12 strings guitars.

I am setting up a 12 strings guitar and I have found that is difficult to
press two strings, on the same row, that have different diameter with the
same pressure. So I find that if I press the fifth row of strings (0,039 - 0,018) I am able
to press the 0,039 string well but the 0,018 not so well and it rattles
because it is not pressed well. This happens also for the third, fourth an sixth rows (less in the sixth). This guitar has good action (1/16 & 3/32 at 12 fret).

1. Is it possible to reduce this difficulty installing higher frets (this
guitar has 0,04" tall frets).

2. Is it possible to reduce it setting each string row more apart?
(each row is more or less 1/16 apart at the nut and 3/32 apart at the
saddle). Which distance do you recommend?

3. Do you think that it is better to cut nut slots with different height in
the same row to gain more comfortable action at the first fret?

That's all.
I Hope you will find the time to answer me.

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The greatest clarity of sound on a 12-string is the not the result of fret height, or in a difference of slot-depth at the nut for each member of the string-pairs. In your case I see the following difficulties:

1- There is no getting around that a 12 string player has to develop more grip strength than a 6-string player. A beginning 12-string player will have clarity problems no matter what the string spacing or string set up is, until the player realizes that more muscle pressure is necessary to press both strings down firmly for a clear sound. It takes specific hand skills to play a 12-string expertly. So be assured that a weaker player will undoubtedly complain about clarity no matter how expertly made or set up the 12 string is. So as a builder or repair man, you must be ready for that dilemma and not blame yourself exclusively.

2- Your strings are indeed too closely spaced at the nut, if they are 1/16 inch (1.6 mm). That can also contribute to a lack of clarity if the strings clash together, the smaller string being overpowered by the larger. At the nut, the optimum spacing is an average of 3/32, with the trebles a tiny bit less and the basses a tiny bit more. At the bridge, the diameter of the bridge pins is a limiting factor, since it is not good practice to cut grooves into the saddle. However if your pins are very fat, you may make a clearance notch in the bridge pins to insure that the optimum spacing between the pairs is 1/8 inch.

3- Your action height is too low. The thinner string will be the first to be dampened when it strikes the frets. So what is the optimum height? Optimum is the highest action possible, given the limits of the players strength, that is, not so low that the strings jangle and rattle on the frets, yet not so high that the player can't press them all the way down. That's the dilemma: a beginning player will complain of difficult action even at a very low setting, which then makes the strings easily contact the frets; then complain about the lack of clarity. Expert 12-string players have a well-developed grip, but also have developed an instinctive ability to press the strings appropriately and efficiently no matter what the string height. But given the choice, they prefer a high action to a low because they are strong enough to overcome it, and it gives them a better tone and a wider dynamic range.

So the 12 string is not an appropriate instrument for a weak or beginning 6-string guitarist. So don't let them blame you for their own lack of development. You learn to play the 12 string guitar AFTER you have become a competent 6-string player. If a weak beginner insists on playing with a very low action, they must accept a sizzly, jangly, unclear sound until they become strong enough to play with a raised action.

If Ramirez does it, shouldn't I ?

I noticed that you don't use the ebony stripe that goes in the neck. You never even talked about it. I was advised to put one in my necks for stability. Should I use it? I don't have power tools, so it is a pain to insert an ebony (or rosewood) stripe in the neck. What do you think?

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I see these ebony center lamination on Ramirez' guitars, and think, "well, they should know." But no amount of reasoning can persuade me that it is useful for neck "stability". Mahogany is far more stable (lower in reactivity to environmental changes) than ebony. The mahogany neck, which is rather large and massive when compared to that of a thinner and narrower steel-string neck, is well up to the task of withstanding the modest tension forces imposed by nylon strings: barely 36 kg--and only half of that, since the neck bears one half of the stressed string, the soundbox bears the other half. So if "stability"is defined as low-reactivity to environmental changes, it just doesn't seem helpful to put a stripe of very-reactive ebony down the center of exceedingly-unreactive mahogany neck to "enhance" it's stability. If "stability" is defined as low deflection, the ebony strip--which is denser and stiffer than mahogany is over-kill. If deflection of the mahogany neckshaft were a problem, we would see action rising as a result of the neck curving or bending under stress. But I've never seen that on a nylon string guitar. Action rising as a result of string tension has always seemed to result from a stretching of the soundbox, and a rotation of the rigid neck at the neck-body junction, not a curving or bending of the neck shaft.

I can, however, read into the ebony center-strip an effort to perhaps harness or modify the acoustic response of the instrument. Trying to think here, like the very talented folks at Ramirez, I find it entirely reasonable to propose (not affirm) that stiffening the neck--not for structural reasons, but for acoustic reasons--reflects the strings' wave energy towards the far-more compliant soundbox. Or that damping the neck to modify the tone, hopefully in a positive manner. The neck's total mass, stiffness, and inertia is an important variable in the guitar's tone production. Adding an ebony strip down the middle creates a new variable, and for Ramirez' perhaps, for them, a reasonable justification for inserting an ebony center strip.

Why NOT glue?

I'm readying myself for a classical guitar, and I've noticed in your book that you do not recommend gluing the sides into the headstock slots. This would seem to compromise stability between the neck and the body in the finished product. What are the pros and cons of this practice, and would I be making a serious mistake if I glued the joint?

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I'm not sure what you mean by "stability", but when you consider that everything converging on the neck joint is tightly glued, save for the sides in the slot, the system ends up being completely "stable" regardless of whether the sides are glued into the slot or not. Setting aside the basic woodworking no-no against gluing onto end-grain, there are good, practical reasons for not gluing the side into the slot. But the best solution depends on the quality of fit that you can achieve, of the side into slot.

The ideal would be that the slot/side clearance offered a glove-fit to the side. The seam would be tight and the side rattle-free. In that case, it would be a disaster if you then attempted to include glue into the slot along with the side. You'd have an instant to properly position the side into the slot before it became permanently locked as the side and the slot swelled by a tiny amount. Try it on scrap, you'll see. If it slides in with no wobble, it'll lock virtually instantly when you slide it in with glue. Another bad thing would be if any glue were to be squeezed out on the show side, it would be unsightly and difficult to completely remove.

I happen to be able to control my slot and side widths so I can achieve a glove fit--one which require no glue. Many experienced builders such as myself do not glue the slot in also, but they've also learned from bitter experience that if you do use glue, you need to cut a generous clearance-fit to avoid the hydraulic locking problem. But then a generous clearance can lead to a visible gap on the show side, which is structurally trivial but visually, very disconcerting. So the solution for builders who don't have the resources to consistently produce a glueless glove-fit between slot and side is to cut a rather wide slot for a wobbly fit; then during assembly, they slide a tapered veneer wedge, with glue, behind the side in the slot. This pushes the side against the slot wall on the show side. And everything is glued together so your "stability" worry is relieved.

But try gluing a side into a tight slot only at your peril! You may loose both your side and your neck in the process.