Marking the saddle. Now it’s time to draw guidelines on the saddle crown for both the individual intonation points and the various angles needed to guide the strings as they emerge from the pin holes (Photo 4). But before you start drawing lines, let’s take a moment to discuss where the strings should sit on the top of the saddle. First we’ll deal with the intonation points, then the string angles.
Fair warning: Setting the intonation entails some trial and error. You can estimate where each string should rest on the saddle, but it’s nearly impossible to get it perfect on the first try.
For this task, it’s helpful to mentally divide the 12 strings into three groups:
• The six E, A, D, G, B, and E strings you’d find on a regular flattop. We know the lowest four are wound, and the top two are plain. So far, so good.
• The plain octave strings (E, A, D, G) that pair with the wound E, A, D, and G strings.
• The doubled unison B and high-E strings. Just like their mates, these are plain.
Okay, think about the first group—our standard 6-string. As a general rule, both the low E and B strings intonate best at the rear edge of the saddle (closest to the bridge pins). The G string’s intonation point is typically at the very front of the saddle (closest to the soundhole).
That leaves the high E, D, and A strings to be accounted for. The high E will typically fall between the B (remember, that’s at the rear of the saddle) and the G (at the front of the saddle). The D and A strings usually create a stair-step pattern between the G and low E strings, with the D closer to the G, and A closer to the low E.
The four plain octave strings are a different story. Both the low E’s octave and the G’s octave points will be at the front of the saddle. The octave strings for A and D will be further back toward the bridge pins.
As you’d expect, the unison B and E strings sit at exactly the same point as their siblings.
Now consider how each string travels from the pin hole in the bridge to the top of the saddle—the intonation point. On this Martin, the six primary strings—those that correspond to a standard flattop—are set back toward the rear of the bridge. The six additional strings, the four octaves and two unisons that make a 12-string such a beautiful beast, emerge through the soundboard and bridge right behind the saddle.
On the rear of the saddle, you need to file individual angles (think of them as ramps) that allow each string to reach its intonation point without encountering a sharp edge. Correctly filed angles minimize string breakage and maximize sustain. The angle for the primary strings will be shallower than the six extra strings.
Filing the saddle. This is where your inner artist gets a chance to shine. Using a miniature flat file, carve each string’s intonation point and rear angle, based on your markings (Photo 5). Go slowly, and to prevent any sitar-like buzzing, be sure each string leaves the saddle from a crisp, defined peak as it heads toward the soundhole.
Checking intonation. As I mentioned earlier, there’s a lot of trial and error involved with intonating a 12-string. Once you’ve done the first pass of filing, put on a fresh set of strings, tune them to pitch, and check the intonation.
The goal is to have the fretted note at the 12th fret match the corresponding 12-fret harmonic. Use a tuner to keep track of how close the fretted note comes to its reference harmonic. If the string frets sharp, file the intonation point back toward the rear of the saddle. Conversely, if the fretted note is flat, carve the intonation point forward toward the front of the saddle. When you’re done, the saddle should look similar to Photo 6. Don’t be dismayed at how many times you’ll need to slacken and remove the strings, file the saddle, restring, retune, and recheck the intonation.
Wrap it up. When you’ve got the intonation dialed in to your satisfaction, take off the strings one last time, pop out the saddle, and then polish it with 400 grit sandpaper, followed with a polishing cloth. Restring, retune, and you’re good to go.This process takes a long time to master, but in the end, it’s worth it when your 12-string plays in tune all the way up the neck.