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Neck block w/Support Tongue extension

In response to requests, here is a write-up of the neck block with tongue extension that supports the guitar top under the fingerboard extension.

The photos show the components of the end block, and their relationship to each, the truss rod relationship, a completed block inside the body and the final mortise ready to accept the bolt-on neck tenon. My neck block is 1.5" thick x whatever height is needed for the particular body it's used in. I cut them all long, trim near final length and radius off the end with the back raius dish when doing the sides. You may or may not need to radius off the face that glues to the sides depending on your body shape. I have jigs to hold the finished block if it's going into a "rounded" shouldered body versus the more "square" shouldered bodies such as Martin style.

The “tongue” is constructed from .5” thick mahogany (or .5" birch plywood as an option) and is 2.75” wide. It is trimmed to length to suit the application (body size and 12/14 neck joint) and should stop just short of the transverse top brace. I use a 3/8" ball end router bit on my table router to make the curved truss rod access slot in the tongue. The tongue is glued to the end of the actual neck block blank. I have never had a failure of this joint, but if you are concerned you can always add a dowel on either side of the area to be mortised and this should make the area virtually indestructable.

The purpose of the tongue is to 1) support the fingerboard extension of the soundboard, 2) provide a base wider than the fingerboard extension so that potential cracks in the top, adjacent to the fingerboard extension and running with the grain, are eliminated, 3) eliminate the need for the “Popsicle” flat brace previously used in the preceding item and 4) to free up the upper bouts of the soundboard to contribute to the sound/tone production of the instrument. This last item may be up for discussion, but I feel there is tone (probably in the higher registers) to be had by freeing up this area of the soundboard.
In my particular application, the tongue forms a 90-degree interface with the end block, but you can bevel it to match any neck set angle you may be using...as noted in the drawings in an earlier post. This allows my fingerboard to run onto the top in a dead flat plane. It works for me since my top ”arch” begins about midway in my sound hole and proceeds down into, and through, the lower bout of my top. That has the added benefit, again in my build approach, of having the bridge rotating into a slight “uphill” slope on the top when under string tension. Therefore, before I ever experience a top “caving in” between the bridge and sound hole, the top has to be rotated into and through a flat plane before any dip can occur. It’s just a bit more pre-design to hopefully eliminate a potential problem later in the instruments life.

The truss rod photo shows an LMI single action truss rod and it’s relationship to the neck joint and access from the soundhole. As you can see, I use a mortise and tenon neck joint. Photos of the completed body with all the cuts required to accept the finished neck. Not shown is the .250" hole drilled in the center of the transverse brace. This hole aligns with the curved slot in the tongue and allows the hex adjusting wrench to slide right into the tension nut on the end of the truss rod.
I hope this is of benefit to the other builders. Any question may be directed to me via PM.

PS: Photo quality varies as these were shot at varied times in the past, on different instruments and some were staged (after other steps had been performed) to get the entire process.

Hank Mauel

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Hank Mauel

Thank you for that Clear and well illustrated. The neck block extension seems an effective and relatively simple thing to do. However, this:



is the kind of precious morsel of information that makes hanging out online so worthwhile. That is simply brilliant. It's like, I dunno... using the top dome the way God intended. Just elegant. Thanks again, you rock!

Peace,
Sanaka

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...imagine there were no hypothetical situations...

Hey Hank, I usually glue the tongue to the block with the slot facing the other way round, this way the truss rod is hidden from view inside the guitar...Does this make any difference structurally?

Bill S.

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Dream to be a luthier

I doubt it would have anything but a miniscule effect. The overall area of the slot is such a small percentage of the tongue area that it shouldn't be an issue. The only thing I can remotely envision is the thinned area at the top of the slot curve might crack in your example, but by the time enough force gets transferred to that area, the entire guitar would probably be kindling!

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Hank Mauel

Well, the Law of Averages eventually catches up and you get something right...or more succinctly: Even a blind pig finds an acorn once in a while.

Glad the info was useful and an inspiration. That's what we're all here for.

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Hank Mauel