Putting a tiny bit of radius on a classical fingerboard...

[Paultergeist]

Greetings!

This is somewhat of a follow-up to an earlier post, but I wanted to solicit a few further thoughts from those more experienced than myself....

I have a moderately higher-end classical guitar which is going to need a fret-job. In concert with the fret-job, the fingerboard of the guitar has a slight reverse radius -- a slight concavity, if you prefer -- which makes the guitar a bit harder (for me) to play. I must assume this concavity to the fingerboard is some sort of defect associated with the construction or materials. (By the way, the builder has been consulted -- his suggestion was that higher frets might deal with the issue. As the guitar is over 10 years old, he was unwilling to address the matter as a defect).

Since the fretboard would at least need to be planed flat, my plan is to actually add a tiny bit of positive radius to the fingerboard. I am somewhat at a crossroads as to the radius to specify -- (a) I am interested in giving the guitar a tiny bit of an easier *feel* to play with the tiny touch of radius, but (b) should I ever need to sell this instrument, I don't want to put so much radius on it that it is un-appealing to *real* classical players. That is somewhat my dilemna.....

Having looked around and played any nylon-string instruments I could locate which did have a tiny touch of radius, I am steering myself towards a 24" (inch) radius; this is also the amount used by La Patrie on their "classical" guitars, and the degree of radius is really not noticeable unless one really studies it, but it might just make the guitar a tiny bit more comfortable.

I would be appreciative of any thoughts or opinions on this 24" radius before I drop the guitar off at the luthier's and give the go-ahead. I guess I am just a little nervous about "what" amount of radius to specify. Any suggestions are most welcome.

Thanks very much!

P.S. Still gotta decide on frets too......sigh.....

[LouieAtienza]

It's possible the center of the fretboard shrank more than the edges since the edges are protected by finish.

I am by no means an expert on classical guitars, but I have used 20" radius on my nylon string fingerboards. 24" is pretty flat, and personally I do find it way easier to play. I guess you'd have to weigh the value of resale versus the value of your own enjoyment on the instrument. I don't know if it would degrade the value so drastically, though if can limit the number of times the board could be planed down (if it were to be returned to flat) before other corrective actions need to be taken.

[charles Tauber]

Originally Posted by Paultergeist

I must assume this concavity to the fingerboard is some sort of defect associated with the construction or materials.

Many years ago, I made a 7-string classical with an ebony fingerboard that was purchased locally. The fingerboard was flat sawn. It eventually cupped as you describe. Planing it flat or convex, as you propose, was required to fix it.

The amount of curvature and fret height are a matter of personal preference.

[Ned Milburn]

I have radiused both classical guitar fingerboards as well as the surface of the fret plane.

I'd suggest this for a starter. Plane the fingerboard flat. Then, choose some frets with a bit extra height, and you can add a bit of radius to the fret-surface plane. I have even planed a curvature from the g-string to the edge of the fret on the treble side, with a flatter fret surface from D to low E.

You don't really have to concern yourself with a particular radius. I have been working on guitars for 20 years, and don't think I have measured a fingerboard radius yet.

[redir]

I've had this happen to me on one of my guitars with an ebony flat sawn board as well. It's almost impossible to see the end grain in an ebony board to read it properly so you know how to glue it down, or at least I don't know the trick to it. When you are using a flat sawn board, and BTW most are now since good ebony is scarce, you want to glue it down such that the end grain (annular rings) are cupping upwards so that when it expands it actually will give you a bit of fret board radius. Ideally the guitar would be takin care of properly so that this expansion never happens but in the real world it does.

You can probably test this by subjecting the ebony board temporarily to dry and unfriendly conditions, note the cupping and proceed as necessary. I've not tried that. Typically it's not a huge problem.

Deck builders and furniture makers will alternate the cupping when joining boards so that one cups up, the next cups down, and so when you get expansion there is an 'equal' tension between them resulting in the best fit for flatness.

As for actual radius for classical guitars it's a matter of preference. I've used a 20 degree on a few guitars that are more or less cross overs, one was a Flamenco but at any rate it's a matter of preference. I'm hardly an aficionado on the classical guitar but my personal preference is for dead flat.

Actually what I do on my dead flat boards is taper the bass side down from the nut to the end of the fret board towards the bridge on the bass side. So that gives it some sort of 'action' there.

[John Arnold]

Concavity is caused by shrinkage, not necessarily because the edges of the fingerboard are finished. Ebony is more unstable than commonly-used neck woods like mahogany or Spanish cedar. In other words, it shrinks more across its width than the neck wood, pulling it into the concave shape. This is more common in flat sawn wood, and it will tend to do the same thing whether the fingerboard is glued where the rings are concave up or down.
This shrinkage is often caused by the moisture in the glue used to attach the fingerboard to the neck. Wood swells with the added moisture, but the clamping procedure holds it flat. After the glue sets, the moisture leaves the wood, setting it up for the differential shrinkage. This can be remedied by waiting for the moisture to completely leave the wood before surfacing the fingerboard. This may take several weeks.
I think a 24" radius would fit your requirements just fine.

[Trevor Gore]

What John said.

I build a non-flat fretboard as standard on my classicals; basically a radius too large to measure. The radius is so large that the flat-earthers don't ever notice it, but it's sufficient to make sure the fretboard never goes concave.

I also do radiused fretboards for those (many) who prefer them. I use 20" mostly, which seems to be a happy number for classical players, but I have a demo classical at 12" just so people can try it. Those who play both classical and steel string tend to prefer the smaller radii (12" or 16").

[Paultergeist]

I continue to be very impressed and appreciative by both the technical expertise as well as the willingness to share knowledge which I have encountered on this forum. My sincere thanks to all who have replied to my query.

Originally Posted by redir

...Ideally the guitar would be takin care of properly so that this expansion never happens but in the real world it does.

You can probably test this by subjecting the ebony board temporarily to dry and unfriendly conditions, note the cupping and proceed as necessary...

From what I can deduce, the guitar did indeed get drier than it should have. The case I keep it in has an integrated hygrometer, but I have now come to realize that this integrated hygrometer is not working. I attempted to *investigate* the humidity effect by placing (2) wet sponges in perforated plastic bags in with the guitar (in the closed case), but storage of the instrument in this manner has made no perceivable change to the reverse radius (or "cupping") of the fingerboard.

My understanding of the fingerboard material is that it is indeed ebony; it is beyond my expertise to comment more fully regarding some of the other issues raised (quartersawn, annular rings, etc).

One interesting historical point is this: At about (3-4) years after purchase (I purchased the guitar new about 10-11 years ago), I had an interaction with the original builder where he examined the guitar. He noticed at that time a very faint tactile *feel* of an edge along the treble side of the neck where the ebony fingerboard wood and neck wood joined. My assumption -- even at that time -- was that there was some sort of differential shrinkage of the two woods. To his credit, the original builder stated that he was not comfortable with this issue, and he took the guitar from me, removed and re-attached the fingerboard free of charge. The builder stated that he felt that the original glue (fingerboard-to-neck) had partially released, and that it was the partial failure of the glue which caused the issue (he stated that he used a superior glue for the repair). It is my understanding that the original fingerboard was thus removed and re-atteched. Just some history.....

The luthier slated to do this current repair (not the original builder)-- a person I like and have quite a bit of confidence in -- does not intend to remove the fingerboard. He and I had discussed this a bit -- he feels (as do I) that the ebony wood fingerboard is pretty *stable* at this point of time and age, and there is no sign of it (again) delaminating from the neck wood (as it did some years ago when the original builder repaired it). In a nutshell, the feeling seems to be that the ebony shrank, but that it is by now done shrinking. This (intended) repair job would thus entail fret removal, re-planing/radius-ing of the fingerboard, and new frets (dressing, etc)......this is my current plan-of-action. I only bring this up because -- in the course of getting a couple of estimates -- a contrasting opinion for this repair involved a complete replacement of the fingerboard (about 3x the cost of the re-plane / re-fret). I suppose there are legitimate arguments to be made for either approach, but I am going with the option which feels right to me.

For any who were curious, I did show the guitar very recently to the original builder of the instrument, but it was my strong impression that he was not interested in repairing the guitar.

Thanks again to all for the information and support.

[arie]

Originally Posted by John Arnold

Concavity is caused by shrinkage, not necessarily because the edges of the fingerboard are finished. Ebony is more unstable than commonly-used neck woods like mahogany or Spanish cedar. In other words, it shrinks more across its width than the neck wood, pulling it into the concave shape. This is more common in flat sawn wood, and it will tend to do the same thing whether the fingerboard is glued where the rings are concave up or down.
This shrinkage is often caused by the moisture in the glue used to attach the fingerboard to the neck. Wood swells with the added moisture, but the clamping procedure holds it flat. After the glue sets, the moisture leaves the wood, setting it up for the differential shrinkage. This can be remedied by waiting for the moisture to completely leave the wood before surfacing the fingerboard. This may take several weeks.
I think a 24" radius would fit your requirements just fine.

i know it's not traditional, buy one could always use epoxy. it removes glue moisture from the equation. now you could say that yes, getting the fingerboard off will be hard, but is it really that important? imo the fret board to neck bond isn't a "service joint" like the bridge or the neck block where these days one expects to re-glue them in the course of a reset or a bridge lift.

[Alan Carruth]

What John and Trevor said.

I believe this is an example of 'shrinkage hysteresis'. When a piece of wood is put trough a moisture cycle it shrinks and swells. Assuming the R.H. of the end points is the same every time (say, 20% and 90%), the piece never quite swells back to it's original size when the moisture is brought back up. The next time it drops the piece gets even smaller, and so on. The first time I heard about this was back in the 80s or so, in an article in 'Fine Wood Working', where a furniture maker was looking into it in connection with frame and panel construction. Anyway, for whatever reason, ebony seems especially prone to this. As the board gets narrower it pulls in the edges of the neck, and the surface goes concave.

This can be a real problem for the player, since it makes barre chords a lot more difficult. The first time I noticed this on a guitar was a repair that came in for fret work. The owner was having enough left hand trouble that he was thinking of quitting playing entirely, but hoped that maybe some taller frets would give him a new lease on his playing. A very slight radius (barely perceptible) and good level frets were all it took.

What's interesting to me is that the flat fingerboard must be fairly recent, as such things go. On early instruments with tied frets the 'board was arched slightly to keep the frets in good contact. Fret gut can be pretty stiff. It can make enough of an arc coming around the corner to produce a gap underneath, and we all know what a problem loose frets are.

I suspect the 'dead flat' fingerboard is one of those workmanship things: it looks more 'exact' in some ways than one with a little bit of a crown. It would not be the first time that 'good workmanship' and 'proper function' turned out to be at odds.

[Paultergeist]

Great, insightful comments. Thanks very much to everyone.

Originally Posted by Alan Carruth

....This can be a real problem for the player, since it makes barre chords a lot more difficult. The first time I noticed this on a guitar was a repair that came in for fret work. The owner was having enough left hand trouble....

A similar story here with me......for some reason, the guitar has felt a bit harder to play. I never really pondered why (I should have!) but did not really identify the key issue until I lent the guitar to my instructor -- it was he who pointed it out to me. Now -- as the cupping effect is readily visible -- I don't know why I never figured it out before. Kind of a *duh* (slaps forehead) moment for me at this time. I wonder if it was always that way, and I just didn't realize it when I bought it?

I have been wrestling with left hand pain for a while now. While not all of the issue is a direct result of playing this guitar (I have a couple of other instruments), I suspect it is a contributing factor. I am looking forward to the resolution once the guitar gets repaired.

Thanks again to everyone.

[John Arnold]

I only bring this up because -- in the course of getting a couple of estimates -- a contrasting opinion for this repair involved a complete replacement of the fingerboard (about 3x the cost of the re-plane / re-fret). I suppose there are legitimate arguments to be made for either approach, but I am going with the option which feels right to me.

Nothing you have said here would lead me to believe that a total fingerboard replacement is necessary, or even desirable. IMHO, it is better to leave that joint undisturbed unless it is absolutely the only viable option.

[Paultergeist]

Update: This repair took a remarkably long time to complete for a variety of reasons, but I just got the guitar back from the shop yesterday. I am still "feeling it out," and I will provide more insights as I get to spend more time with it, but the slight (24") radius coupled with a set-up has made the guitar much, much easier to play. Another classical player also played this guitar and noticed the radius right away -- myself, I really have to study the fret-board to visually discern the 24" radius. Maybe I should have gone even shallower (say, 30"?) but I have cast the dice with 24". It really doesn't look or *feel* radiused -- it just feels a lot easer to play. I am hoping that I will continue to appreciate the change.

The strings put on the instrument after the repair are not so much to my liking; I will have more to comment on once I get some better strings on it.

Thanks again to all for the continued dialog.