This was an interesting year of communications. One question that came up several times was about how to make a tall bridge to compensate for a dovetail neck joint that was accidentally crafted with the wrong neck pitch.

My answers typically led us through a discussion about "string break angle," and I found myself thinking of the old sailing phrase, "Don't raise the bridge, lower the water!"

Although raising the bridge to compensate for severe neck pitch will solve the problem of achieving a playable action at the fretboard, it poses a real threat to the soundboard. Here's what happens:

The "string break angle" is the angle the strings make when they pass over the bridge, and this angle is very important bacause it determines the download on the soundboard at the bridge feet. A 16° string break angle is ideal. And, on a properly set up F5 mandolin with a 6° neck pitch, the resultant string break angle will be 16°. If the instrument is fitted with D'Addario J-73 strings, the download on the soundboard will be 45.5 pounds.

It is important to realize that a change of 1° in neck pitch will result in an increase of a 4° string break angle! So, if the neck angle accidentally gets set at 7°, the string break angle at the bridge increases to 20°, and the download increases to 62 pounds! (An Adirondack Red Spruce mandolin soundboard, properly graduated with tone bars attached, will rupture at about 80 pounds.)

None of this has anything to do with the physical height of the bridge - it is directly related to what angle the strings make as they bend over the bridge, and that determines how much of the load is directed toward the soundboard.

The problems associated with getting the neck pitch correct when setting dovetail joints - especially when doing them by hand - is one of the main reasons I strongly urge considering the "V" joint. It is much more forgiving and allows greater flexibility in setting the joint when arriving at the correct neck pitch. If you are interested in learning more about the various loads associated with string break angles, you might want to take a look this string break angle study in our web site.

If you are using dovetail joints, take great care in getting the neck pitch right. A pitch of 6-1/2° is fine, but I would refrain from using anything greater.

And, if you find yourself in a pinch with a neck joint you've put together that presents a string break angle of more than 16°, email or call me and we'll talk about various ways to solve the problem.