Upper Bout Jig

UPPER BOUT ANGLE JIG

It’s always tough to get the angle of the upper bout so that it matches the angle of the fretboard when the neck set is proper. A 28’ radius on the top gets you close but still needs tweaking. I pulled a 30’radius out of the air when I started building and am too lazy to change all my jigs so I need more tweaking.

I start by using flat braces above the soundhole and radius the rims and kerfing to 30’ in the usual manner with a sanding disk.

The jig consists of a transverse bar that goes across the rim at the level of the bridge. The front of the bar is about 1/16” thicker than my bridges. It is positioned right where the front of the bridge would be and clamped. It has a pivot point for the sanding board.

The board itself is plywood with a 1/4” piece of plexiglas attached to represent the fretboard. Mark the rims with chalk to the level of the upper soundhole and sand away. This will profile the rims so that when the top is on you can clamp a fretboard to it and a straightedge will clear the bridge by about 1/16”

I usually fine tune things with the Fox paddle after the top is on, but very little sanding is usually needed.

Here’s the sanding board with the 1/4” plexiglas attached and 80G sandpaper

Here’s the sanding board set up to sand the angle into the upper bout

Here is another view of how the sanding board hits the upper bout. After the top is glued on I flatten it if needed under the area of the fretboard and make sure the angle is right. I then transfer that angle to my tenon routing jig for the neck tenon. This puts the cheeks at the right angle and gets everything very close without too much messing around setting the neck. This system has really simplified a process that used to really give me fits. No more fretboard drop off and hours of messing around getting the neck set right!

Fox type tenon routing jig. The metal arm sticking out of the top gives you the angle of the neck and can be matched to the angle of the upper bout you obtain with the sanding jig.