Guitar conversion?

nicksansone · November 2016

Hi all luthiers,
Is it possible to take a short scale 12 fret to the body guitar and change out the fretboard to a 14 fret system while keeping the same scale length? Would you have to move the bridge, and therefore put it in a position where there isn't a brace and jeopardize the structural integrity? I know it sounds like a bad idea, and I don't really have any interest in a "just buy a 2 guitars if you want a 14 fret model" response; so if anyone can answer this question I would be very interested to hear. Thanks in advance.

Buco · November 2016

Yes, AJL can make you one:
http://www.ajl-guitars.com/ajlguitars/index.php?id=135#.WCXiSZ9OnJA

ChrisFromTheBMT · November 2016

Hi, you probably *can* convert the guitar, but (as you anticipated) the bracing will be an issue in the long term. When the fingerboard moves away from the soundhole by 2 frets, the bridge moves toward the soundhole to compensate. If you look at the bracing on these guitars, the bridge sits right between two horizontal braces and right on top of two short braces that run along the long axis of the instrument. Without re-bracing the top, it looks like the bridge would be putting lots of stress on an area that is relatively unsupported.

nicksansone · November 2016

To be more accurate I'm asking if the fingerboard/scale length is the same but the fret layout changes to 14 instead of 12 ( just replace the fingerboard and put 14 frets) would anything have to change?

@ Buco : on a preexisting guitar

Jeff Moore · November 2016

The answer to your last question is yes. You can't have the same scale length and create a 14 frets to the body with a new fretboard.

By doing this, you'd "force" the bridge quite a ways further towards the sound hole and now the bracing is out of whack. The bridge would not sit between braces but almost on top of a brace. Obviously the mustache ends would have to follow the bridge to this new position.

Just think of it this way: The 12th fret must be half way between the 0 fret and the bridge. Adding two frets at the body joint (without lengthening the scale) pushes that mid point (12th fret) further down the neck towards the head of the guitar and the bridge will have to follow the 12th fret.

There's a reason the bridge on these guitars sits nicely near the middle of the lower bout. That reason is that the scale length is an inch or more longer than typical guitars.

ChrisMartin · November 2016

If I have read your question right, you have confused two different sets of measurements so what you ask is not possible without making a new neck. The scale length is the distance between the nut (or zero fret if fitted) and the bridge, or put another way, the length of the unfretted vibrating string. The fingerboard length is determined by the length of the neck plus whatever extension is added on the body. A scale length of for example 650mm needs the 12th fret to be at 325mm from the nut or zero fret, and if the neck joins the body at the 12th fret, then that is the length of the neck from the nut to the body. I don't have the formulae for calculating exact fret spacing at hand, but if you replace the fingerboard to accommodate 14 frets to the body on the same neck, you must therefore be shortening the scale length at the same time as the 12th fret is now approximately 30 or 35mm north of the body join, meaning a distance from the nut to the 12th fret is now less than 300mm which equals a scale length of less than 600mm meaning the bridge has to move more than 50mm to compensate.