Guitar Maintenance Set-up & Intonation
by Wayne Sixfinger SeversonIn the tuning section I briefly discussed the physics of string length, tension and the resulting frequency or pitch. The theoretical position of the saddle on the bridge is exactly double the distance of the nut to the twelfth fret. For an accurate measurement measure from the forward edge of the nut (the edge closest to the frets) to the center of the fretwire. Do this in a straight line, the same line of the string. Any increase in tension on the string will raise it's pitch. When you press the string down against the fret you are increasing the tension and bending the tone sharp. The idea here is to compensate for this increased tension by lenghthening the string. This is done by moving the saddle farther away from the nut. This is called String Length Compensation or setting the intonation.
Before you begin the first thing to remember is that Everything Effects Everything. What this really means is any adjustments made to the guitar will change the intonation so adjusting the saddle position should be the last thing you do. For now let's assume everything else has been done. The truss rod adjustment, the slots in the nut are spaced right and filed to the correct width, angle and height. The frets are in good shape with a nice crown. The neck is set at the proper angle. The saddle/s are at the right heigth to give the desire action. If the guitar is electric, the pickups are at the correct height, etc. We want to work with a new set of strings of your brand and gauge (any changes will affect the intonation). There are a few effective techniques for installing strings. One standard is to insure there are a minimum of three wraps around the tuning post to preclude slipping. You must also let the guitar settle in. I will rough tune the guitar then grab each string one at a time near the center of its length and gently tug it upwards, away from the body and neck, to stretch it and to remove any slack in the wraps. Don't over do it as you can damage or break the string! Tug and tune, tug and tune, then play and tune for about fifteen minutes. the idea is to have everything as close as possible to the real world performance standards as you're making the final intonation adjustments
Electric guitars usually have adjustable saddles at the bridge. We'll talk about these first. Most bridges have a simple screw adjustment which moves the saddle either towards or away from the nut to facilitate shortening or lengthening the string length, (the distance from the nut to the saddle). You can leave the guitar on the bench for your first checks, but your final tests for adjustment should be done in the playing position because the weight of the neck can at times be enough to affect a change. The best thing to do before turning adjustment screw is to detune that string to take the tension off the saddle. Some bridge designs allow for smooth adjustment without this step, but if the screw is difficult to turn, then loosen the string first.
Using an electronic tuner, play the tuned string open, then fret the string at the twelfth fret. The pitches should match! If the fretted note is sharp compared to the open string you must then lengthen the string. Turn the adjustment screw so the saddle moves away from the nut. If the fretted note is flat, do the opposite. Do this to all strings until they all match up.
NOTE: It is important to consider the tremendous affect the player can impart on intonation by the amount of pressure used in fretting the guitar. As an experiment try various amounts of pressure on the frets while watching your tuner needle. With high or large frets its easy to go way sharp. Sloppy technique can also cause the string to be bent up or down also causing sharpness. To a small degree you can adjust the intonation taylored to the player (a very good reason to learn how to do this yourself). If you play with a heavy hand leaving the intonation a bit flat may compensate for your technique. Keep in mind as you learn to play you can and should also learn to play in tune by using the right touch and listening carefully.
I have notice on some bridge designs where the saddle height is determined my set screws acting as posts or legs, and when the adjustment screw head is considerably lower than the top of the saddle that as you pull the saddle away from the nut by adjusting the screw, you are effectivly raising the action at the same time because of the angles involved. In these cases you must lower the saddle height as you lengthen the string to maintain the original action and successfully adjust the intonation.
Another Note: The basic theory to be aware of to give you a close starting point is that thicker string gauges require more compensation (more length), and gauges being equal, plain strings require more compensation. This means the low E string saddle will be the furthest from the nut, then the A string saddle will be in a little. Then the D string saddle will be in even more. Next, if the G string is wound, it will be in even closer to the nut. But if the G string is plain it will have to be pulled out almost as far as the A string saddle. Then the B and E string saddles will stagger inward as shown;
Saddle Positions with plain G String
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Saddle Positions with wound G String
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A Note on 3 saddle Telecaster Bridges: In the 50's when this was designed it was very common for guitarists to use a wound G string. Under these conditions the 3 saddle Tele bridge can get you very close. Modern guitarists who use a plain G string should replace this bridge with one that has six individual saddles if they want to play as in tune as possible. There are many available which fit exactly and require no drilling so you can keep your original bridge for the best resale value.