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Pay close attention to the angle of each string in relation to the tailpiece. The tailpiece should be adjusted so the strings never touch the rear edge of the Tune-o-matic. Contact here can cause tuning problems, so all the strings need to clear the bridge frame (Fig. 5).
Fig. 5. Set the tailpiece height so no strings rest against the rear of the bridge frame. The only point of contact for each string should be the top of its respective saddle.
When the tailpiece is adjusted, I finish filing the string slots. This involves carefully sloping down the back of the slots to allow each string to follow its natural angle as it emerges from the tailpiece to the point where it contacts the saddle (Fig. 6).
Fig. 6. File the saddle slots to allow each string to follow its natural angle to the tailpiece.
The final step is to intonate the guitar by moving the new saddles forward or backward in the bridge to shorten or lengthen the vibrating portion of the string. The saddle-intonation adjustment screw is located at the rear of the bridge, and the idea is to move each saddle forward (by turning the screw counterclockwise) or backward (clockwise) using a small screwdriver. (Typically it’s a Phillips or flathead, depending on the make and model of the bridge.)
Here’s how to set the intonation:
1. Using a high-quality electronic tuner, bring each string to pitch. But instead of playing an open string and tuning it, strike the 12th-fret harmonic and tune it to pitch.
2. Starting with the 1st string, play the 12th-fret harmonic and then fret and pluck the same note. If the fretted note is sharp compared to the harmonic, move the saddle away from the neck. Conversely, if the fretted note is flat, move the saddle toward the neck. Make small adjustments and retune the harmonic each time you make an adjustment. Continue comparing the 12th-fret note to its reference harmonic until the former matches the latter.
3. Repeat this process until all the 12th-fret notes on all six strings match their corresponding 12th-fret harmonics.
Once the strings are intonated and you’ve confirmed they’re spaced, seated, and angled correctly, you’re good to go with your new Tune-o-matic.
Smiling Bridge Syndrome
The last thing you want to see is your Tune-o-matic smiling ... as if to mock you! When this happens, it means the bridge has collapsed, causing the action of the middle strings to drop lower than the outside strings. Many Tune-o-matic-style bridges are made of zinc—a metal that’s softer than steel—and years of downward string pressure can destroy the bridge’s built-in radius that’s designed to match your fretboard.
You can check this with a 6" machinist’s metal ruler. Fig. 7 shows the original, collapsed Les Paul bridge, and the large gap between the ruler and the top of the bridge frame reveals the problem. Notice how the ruler lies flat against the top of the new replacement bridge (Fig. 8).
Fig. 7. See the gap in the middle of the bridge between the ruler and frame? Years of string pressure have caused this bridge to collapse, dropping the middle strings lower than the outside strings.
Fig. 8. This new bridge has no gap. Once it’s installed, the Les Paul will be playable again.