One pic = 1K words

[ken cierp]

Why so big? 1/8" depth would be just as effective. Those splice tenons add zero strength to the joint, maybe compromise the neck block? They are merely locators, which leads right to -- have two bolts (takes care of the perpendicular) and also adds real strength, countering the lever action of the neck string tension. Oh wait! That's been done before.

[Dave Bagwill]

The splice tenons are glued into the heel with HOT HIDE GLUE , boys and girls, so there is nothing to worry about.
Just kidding :-)

[Dave Bagwill]

More importantly, I did find a pic of the early Taylor butt-joint system. Man it is simple, and worked great. Got the pic from:
http://www.frets.com/FretsPages/Luthier ... reset.html

[ken cierp]

My experimental "lab guitar" constructed 1980 ish, has that style joint retrofitted from a dovetail, still going strong for 8 or 10 years now. On that one the FB extension is glued to the top cut off at the 14th the fourteenth fret covers the seam at the slot. Also I have a 1/2" dowel running all the way thru the heel. You can see it in the pixs

[Dave Bagwill]

Ok. A hardwood dowel to hold the inserts better?

[ken cierp]

Correct

[Dave Bagwill]

What in general would be the recommended minimum thickness of the heel on a butt-joint? Here is a picture of a sweet heel from a gypsy guitar, but of course they are traditionally dovetail joints.
For a butt joint, the heel looks a little thin? Is there a good minimum thickness?