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I have been thinking about my neck design and I hate the fact that
sometime despite a lot of work, there is a change in angle at the 14th
fret. (Neck body joint....even with a Woolson jig)
Some of this occurs despite what seems like the perfect neck angle.   
Fretboards can bend a bit etc.   String tension???
To this point I have been using a duel tenon joint. (cumpiano tenon with
a fretboard tenon to hold the fretboard extension down.....Like John
Mayes, Kinnaird etc)
I dont like adding the 2nd tenon on the bottom of the fretboard.
Conceptually if the neck mahogany extended all the way down you could
GUARANTEE a perfectly straight neck.
Does anyone do this? It is similar to Taylor, but I am adding carbon fiber
all the way down. Also, I dont have shims etc to change neck angle.
It seems that adding the heel will be more of a challenge since I just
cannot route the angle anymore.
The picts below show my attempt. Also pictured is my standard neck
block with the baltic birch extension for the fretboard. The tenon will be
thinned a bit and the mortice cut out of the birch
Any advice????

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Andy Z.
http://www.lazydogguitars.com

I've built only one steel-string acoustic so far, so I'm hardly an expert. But I got that 14-fret "bump" on my guitar too. The bump appeared, however, after I'd tightened up the bolts (I used a bolt on neck with cross dowels) a bit more after the fingerboard had been glued down. A newbie mistake, I suppose.

It was suggested to me that the likely culprit was the fingerboard being compressed from snugging the bolts up a bit more, and that one way to alleviate the bump would be to heat up the fingerboard at the upper bout to loosen up the glue (I used Titebond), then reclamp the fb, and that it might straighten out.

This helped a little, but the bump was still detectable. I ended up recontouring the frets to deal with it.

Best,

Michael

_________________
Live to Play, Play to Live

Andy, I do it very similar to the way you do. My method is sort of a hybrid of the Mayes system where I actually cut a mortise in the neck blank and insert the fb extension piece. Once glued in and having the fb on it, it's solid as a rock.
One issue I forsee with your design as it is, is how are you going to cut the tennon with the extension piece in the way? Looks difficult.

Paul,

Do you have a picture of that? I can't quite get it in my head how you insert the FB in the mortise of the neck blank.

Thank you.

Jeff

Paul
That is why I posted the thread. I knew cutting the tenon would be the
problem. I was thinking of cutting on the heel piece before glueing and then
just fine tuning from there

_________________
Andy Z.
http://www.lazydogguitars.com

Andy,

Do you mean like this?

_________________
Dave White
De Faoite Stringed Instruments
". . . the one thing a machine just can't do is give you character and personalities and sometimes that comes with flaws, but it always comes with humanity" Monty Don talking about hand weaving, "Mastercrafts", Weaving, BBC March 2010

Andy and Dave, this is really cool and it makes that task seem easier, i really gotta try this on my next build. Thanks!

Haven't done it yet, but a similar joint has been on the drawing board for at least a year and a half now..slightly thinner fingerboard extension though (more around the 1/2" mark)

EXACTLY DAVE
how do you cut the tenon???? with the fretboard extension already cut????
What order

Thanks
Andy

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Andy Z.
http://www.lazydogguitars.com

I do the same neck extension on mine. I've stopped using a tenon now, but when I did I just cut the tenon onto the block before gluing it onto the neck shaft. If needed, meaning if I botched the gluing, a little correction with a chisel to get everything lined up.

Colin

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I don't believe in anything, I simply make use of a set of reasonable working hypotheses.