Commonly Available 12 String Martin 12 Fret Dreadnaught Plans.

[Gilbert Fredrickson]

Is that body shape identical to the six string, twelve fret Martin Dreadnaught?

[Brent Tobin]

The body size and shape should be the same. Beef-up the X braces and use a trussrod. Irving Sloane recommended using a harder wood like cherry for the neck, but that was before adjustable trussrods.

Brent

[Gilbert Fredrickson]

Thanks. They look very similar. I just finished a mold and a bending form for a J-45. I can make a twelve fret from that.