Actually, neck angle is responsible for achieving a target vertical distance from the surface of the top to the bottom of the strings measured at the bridge. That distance is related to the torque (moment) the strings exert on the top/bridge. For Martin style guitars, that target is 1/2”. The neck angle is correct when the string action is at the desired height above the frets and the 1/2” target is achieved. The bridge thickness is then what is left after the desired saddle projection - about 1/8” - is subtracted from the 1/2” target. That leaves a nominal bridge thickness of 3/8”. Martin uses several bridge thicknesses to maintain the saddle projection with varying neck angles (ie tolerance on 1/2” target).
For classical guitars the target vertical height is 10 or 11 mm, which necessitates a different neck angle than steel string guitars - the nut is higher than the plane of the top, rather than the nut lower than the plane of the top.
For arch top guitars, the target vertical height is often a little more than 1”. (The 1” value is a target for laying a straight edge on the frets and measuring vertical height at the bridge.)
Last edited by charles Tauber; 01-08-2020 at 10:40 PM.
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