Originally Posted by maialinodivino
I don't think a few grams more will add a significant mass to the headstock to generate more sustain, a nice fret job will in any case, but a more rigid and resistant to stresses neckjoint for shure.
Thats not why they add sustain, they add sustain because what kills the sustain on a guitar without a volute is, in part, the fact the headstock vibrates out of phase with the rest of the neck. The fat finger adds mass to increase sustain, but the reason it works isn't the extra mass in the guitar itself, its the fact it means the big panel of wood we DONT want to vibrate, called the headstock, is less easily excited into motion, adds less muddy overtones to the sound, and etc.
The reason it needs so much mass to do that is because what its doing isn't structurally reinforcing the joint like a volute does (the much more effective way of doing it, and also the same concept behind the sustain bows on certain crazy auerswald instruments and roland instruments), but its making it so the headstock is too heavy to move with only the vibration force transferred from the string. (Don't forget, from a sustain standpoint, the ideal, engineering method, would be to have a string where each end was completely and utterly immovable.)
This is also why some people don't see benefits from the fat finger on their guitars - Because a guitar with a volute already has an integral 'fat finger' in a sense, adding a fat finger just makes your guitar neck heavy.
This was explained to me somewhat in detail by Ged Green, a local luthier in manchester, when I went to him to spec out a custom neck.