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When you build a standard acoustic guitar the bridge is
glued on last, so you can move it in order to position the sad-
dle for good intonation. Resonator guitars are different
because the saddle position is determined by the fixed loca-
tion of the cone resting in the soundwell. The cone — and
saddle with it — can be moved forward or backward about
1/16" within the soundwell, but that’s it. You can guarantee
good intonation by never removing wood from the top edge
of the neck cheeks, and by careful placement of the finger-
board.
However, if you did need to make neck-fitting adjustments,
and if you moved the neck toward the bridge at all, you
should check the placement of the fingerboard’s 12th fret
before gluing the fingerboard onto the neck. Here’s what to
do:
When the neck fitting passes inspection, leave the neck bolt-
ed into the body in order to check the lengthwise placement
of the fingerboard — specifically the location of the 12th
(octave) fret in relation to the saddle. This relationship makes
for good or bad intonation.
Since you haven’t glued the fingerboard on yet, you can slide
it forward or backward a little, to control the distance
between the 12th fret and the saddle. (You also have a little
adjustment at the saddle, since the cone will slide forward or
back about 1/16".)
If you do slide the fingerboard, the flat area where the string
nut is located will become wider or narrower, and you’ll need
to fit the nut accordingly. Also, the fingerboard edges may no
longer be perfectly flush with the sides of the neck. (Simply
shape the edges of the fingerboard and neck to match using
a file and sandpaper.)
If minimal wood was removed at the cheeks, locate the fin-
gerboard so that the 12th fret lines up with the point where
the neck cheeks join the body. At the peghead end there
should be approximately 3/16" of flat area left between the
end of the fingerboard and the break angle of the peghead.
This is where the bone nut will rest, and it may be as large as
1/4" or as small as 1/8" if the fingerboard is moved forward or
backward for intonation adjustment.
To get accurate intonation, the distance from the 12th fret to
the saddle should be approximately 1/8" longer than the dis-
tance from the 12th fret to the nut. Since your guitar’s scale
length is 25", the distance from the 12th fret and the nut is
12-1/2". Add 1/8" to get the desired distance from the 12th
fret to the saddle: 12-5/8".
This extra 1/8" is called “compensation,” and makes up for the
slightly longer string length caused by the strings as they rise
up to the saddle, and for the fact that strings tend to go
sharp when they are pressed down to the fret. If you located
the saddle at the uncompensated distance from the 12th
fret, the intonation would be sharp.
Center the cone in the soundwell, then locate the 12th fret
by loosening the spring clamps, and sliding the fingerboard
forward or backward until the 12th fret measures the com-
pensated 12-5/8" distance from the center of the saddle.
When the 12th fret is where you want it, and with the spring
clamps holding the fingerboard on, place a piece of masking
tape on the neck surface at the nut end of the fingerboard —
use this tape as an index to butt the fingerboard up to when
you glue it on.
Appendix 2: Intonation check (optional)
