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Hi group,

I'm in the process of thinking about adding an elevated fretboard extension to my classical model. Now after searching around the web, there seem to be two main design differences: one where the extension is glued to the soundboard, and one where the extension doesn't touch the soundboard.

Any pros and cons of those two designs?


Thanks!

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

And there is also those who bolt the extension down for a completely glue free neck joint.

Indeed, but I consider this to be in the first of the two designs, meaning a 'none touching the soundboard' design.


That is reassuring, since that is what I'm inclinded to do. But my initial worry was on the potential loss of sustain when freting on the extension. I know by experience that there is a considerable loss of sustain on the portion of the fretboard that is hanging over the soundhole (for the 20th fret). So I was kind of wondering if something similar would happen if the entire extension would not touch the guitar. I guess if there is a sufficient amount of wood under the fretbaord, it might be OK.

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

Sonority don't seem to be affected if the board is glued or floating in my builds. However on the floaters, me do use a much thicker fret board, tapered from 3/16 to about 1/2 at the 14th and then the cantilevered tapers to 3/8 at the 22nd which seems to help with the sustain more then your standard 1/4 inch board.










Blessings
Padma

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Audiences and dispensations on Thursdays ~ by appointment only.


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Thanks for the advice Filippo. I will write to Randy and see what comes up.

And thanks for your input Padma.

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

I set a steel plate in the fretboard extension of mine

Yes, you need the extension to have some mass under it and it has to be stiff. I built a few prototypes before going this rout and ended up with about 1/4" of wood under the board at the body joint tapered to about 1/8" at the end. I also use 2 bars of CF, 1/4" wide and the full depth under the extension.

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http://www.chassonguitars.com

Thanks for that info Kent. My plan is to get a substantially more wood than you under the fretboard so I should be OK. That is good to know.

Although I haven't done the detailed geometry drawings yet, I should have something like 1/2" of wood under the fretboard at the 12th fret to about 1/4" at the 20th.

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

Out of the Charles Fox school he explained that the advantage is not in upper bout becoming sonicly active, rather the angle that the strings works the bridge is different. A harp pulls straight on the soundboard, and we are tipping a few degrees in that direction. Charles uses the elevated FB with a double top and his special laminated sides, so he is getting upper bout structure a little differently.

I don't think there is any sound to get from the upper bout without moving the sound hole and going with A frame or other alternative bracing.
However it works, I like it, to me it makes the guitar more play able, easier upper fret access without a cut away, and more space under the strings which is my preference for fingerstyle playing. My extensions are short, free of the soundboard, and have some wood under, so I have not noticed a deficiency in sustain up there.
I would add a picture, but the avatar shows it.

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http://www.facebook.com/robert.renick.7

Thanks for your input Robert.

Seems like my decision is made to cantilever the fretboard extension.

Thanks to everyone for helping me out on this!

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

Humphrey millennium guitar was built with the harp like qualities that Robert mentioned. Personally I don't like the floating look but to each their own. I always think of the fret board extension as being part of the neck joint but obviously you can design for a floater. I think I would embed CF rods to stiffen a bit too.

Does anyone notice an overall loss of stability with the cantilevered necks?
Seems to me that sheer strength from the tongue being glued plays a not insignificant role in preventing the neck from coming forward. I know that I abandoned the double m&t and went back to glueing the tongue for that reason...

For what I understand of the physics involved with regard to the neck joint forward pressure, I believe that as long as I 'replace' the fretboard extension with an L shaped or C shaped neck block, it shouldn't be more prone to shift forward.

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

I've used a double tenon neck on my steel strings for the last 7 years. I copied the Mayes/Wells/Bourgeois technique.



Cutting the mortise in the body removes most of the gluing surface of the top to the headblock and headblock extension. I had some where there was a very slight rotation of the headblock noticed at 6-8 months and required a tweak of the neck set to properly correct.
I think Dana addressed this by leaving a very small gap between the top brace and the mortise block extension from the headblock and gluing the top first after which a slightly oversized piece of wood was placed in the gap to push against and stabilize the headblock.

Lately I've gone to this technique after discussing it with Sylvan Wells and it definitely is more stable. I do not have any that are over a year out yet so time will tell but there is a lot more top glued to the headblock.



At any rate if you are going to make a mortise in the top for the thickness of the fretboard extension support there may be some risk of destabilizing the headblock in rotation. Possibly not a problem in a classical.

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It's not what you don't know that hurts you, it's what you do know that's wrong.

The FB being glued does bear some or the rotational load. Also, by raising things, you increase the leverage on the heel. From what I've seen, the main effect this has is to put a lot more torque on the heel which is why mine are so heavily reinforced. If the heel doesn't bend and is firmly attached, there are no problems. If the heel, is not reinforced, it will bend down over time with steel string tension. May not be a problem with nylon.

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http://www.chassonguitars.com

I think what you say makes sense Alain....

Well, I'm not so sure anymore about the cantilever extension. I haven't seen much out there in the classical world, so I'm a bit afraid I'll be looked at with a weird looks if I go with it. So I'll keep on exploring the 'glued to the top' extension option.

One thing that I'm not sure how to deal with is the method to fit the neck. I'm used to do it without the fretboard on, so with a lot of operating space for the sandpaper. How does one go with fitting the neck heel AND the extension at the same time?

Thanks in advance for any input.

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

It can be a little tricky to remove wood near the FB. If you need for some reason to bring the neck forward usually you need to resort to chisels. I tend to rough fit a touch forward to prevent this, and leave a little room to come back when flossing the cheeks. It only seems to take a few pulls these day to clean things up nicely after finish....

It's unfortunate that the classical world is so stuck in their 'traditions' that they won't accept improvement. You should build one exactly how you think it should be done and then do some serious listening tests of the double blind variety. I also kind of feel that if you build true to your own passion, you will probably find an audience for it. At the very least, you owe it to your own knowledge growth to empirically experience the results of what you want to try.