Body geometry with an elevated fretboard.

[KingCavalier]

Hello all,

I’m hoping for some insight when it comes to building a guitar with an elevated fretboard.

When I build my standard acoustic the top is parallel to the sides and the difference in the body depth from the heel block to the tail block is accomplished from the back. When building with an elevated fretboard would that geometry stay the same or maybe be reversed or maybe somewhere in between.

Any help would be greatly appreciated

[IndianHillMike]

Depending on the height of your elevation, body/block depth, etc., your situation might be slightly different, but essentially when I do an elevated fingerboard I put the body taper in the top instead of the back. I also tend to have a more severe taper on my elevated necks -- my neck block ends up ~84mm instead of my standard of 92mm.

[runamuck]

Originally Posted by KingCavalier

Hello all,

I’m hoping for some insight when it comes to building a guitar with an elevated fretboard.

When I build my standard acoustic the top is parallel to the sides and the difference in the body depth from the heel block to the tail block is accomplished from the back. When building with an elevated fretboard would that geometry stay the same or maybe be reversed or maybe somewhere in between.

Any help would be greatly appreciated

It's most helpful to draw it out full-size. You'll see.

[MC5C]

Keep in mind that archtop guitars have elevated fretboards, typically a 1/2" above the side height, and a neck angle around 4 - 5 degrees. The string plane points at a bridge height around 1 3/4" above the plane of the sides, what with the 3/4" or so arch and the 1" string height above the top. OTOH, classical guitars with elevated fretboards sometimes have a negative neck angle, the string plane points down to meet a saddle height around 1/2" above a pretty flat top. I would start by drawing your top plane, draw in the bridge and saddle height, mark out your fretboard elevation height at the neck block, that will give you your string plane, and drawing a line from the bridge saddle top through the string plane point above the fretboard at the side of the guitar will tell you your neck angle. That - neck angle and fretboard height - is the critical geometry. Box depth can be whatever you want it to be. Archtops and classical guitars often have the top and back perfectly parallel, flat tops seem to be tapered far more often. Once you know where your top is at you can put the back wherever you want it.

[Alan Carruth]

You can do it either way; taper from the top or the back. What is different is the 'overstand'; the height of the end of the neck above the edge of the body, and, of course, the neck angle.

Just imagine that the neck pivots around an axis at the top of the saddle. You can go back a little bit, until the strings touch the edge of the top: tapering the top would actually allow for more of that. You can also tip the neck up, so that the strings are pulling upward on the top, if you want. At a high angle you'd rip the top off, but if the up angle is no more than about, say, five degrees, it should not pose too many structural issues. It won't alter the sound much, either, or it didn't when I did the experiment.

[yellowesty]

Among the benefits of an elevated fretboard is the opportunity to build with a neck whose angle can be easily adjusted by the owner to accommodate personal preferences for string height above the frets. While there are commonly used spacings (e.g., 0.1" between the top of fret 12 and the bottom of string 6), the style of playing and the choice of strings may influence the appropriate action. An adjustable neck angle allows that.

User-adjustability is easily implemented with a bolt-on neck having an elevated fretboard. I use the bolt near the back of the guitar running through the neck heel and then through the headblock to engage a T-nut inside the guitar body. The unsightly head of the adjustment screw is hidden beneath a plug in the neck heel that's penetrated by a hole just large enough (7/64") to allow a small hex wrench to engage the head of the adjustment screw.

In addition to its user advantages, this arrangement allows the builder considerable flexibility in choosing body geometry.

[KingCavalier]

Thanks for the replies everyone, It's very helpful. I'm considering using the elevated fretboard for my acoustic bass, It's based on the plan by Mark Stanley. It's one big bass, the body is 18" wide and 23" long, 50" overall. When I draw it out it looks like moving the taper from back to front should get me close to where I want to be. I still need to do more research before I move forward.

As always, any help is greatly appreciated.