Guitar and Bass Repair - Perfect the Tuning of Your Instrument - Intonation Troubleshooting Part 2

Your guitar won’t play in tune because of faulty intonation. You’ve tried sacrificing your favorite effects pedal to the guitar gods and donating gig money to orphanages, but nothing seems to help. You were ready to take up the Theremin until you found articles like this one that describe practical ways to fix intonation. Part One of this article explained how to fix certain factors that corrupt the intonation of guitars and basses, such as faulty nut slots or excessive neck relief. Part Two will discuss how to fix a few more issues that cause flawed intonation. For a review on how to properly set intonation, refer to the Xylem article "Guitar and Bass Repair: Beyond Basic Tuning - Intonation, What is it and How Does it Work?".

High Nut

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If the first several frets of your instrument play sharp, regardless of intonation settings and tuning, the nut may be too high. The taller the nut the more the strings stretch when fretted. The more the strings stretch, the sharper the pitch. To check if your nut is too high, tune your instrument to pitch and make sure the neck relief is set properly (Articles #1-3). Next, fret the lowest string at the third fret. If you can fit more than one business card between the bottom of the string and the top of the first fret, the nut is too high.

A high nut must be removed and the extra height sanded away. To remove the nut, place a wood block against the side facing the fretboard (Figure 1). Gently tap the opposite end of the block of wood with a hammer to knock the nut free. Most instruments should have only a small amount of glue holding the nut on so it may be removed this way without causing any damage. If the nut does not come off after a few gentle taps, consider asking a luthier or repair tech to remove the nut.

Once the nut is free, mark it to indicate how much material should be removed, keeping in mind that removing 1/8" is a lot. While sanding, make sure the bottom of the nut remains flat and square to the side that touches the fretboard by checking it with a square frequently. Sanding the nut with a jig like the one depicted in Figure 2 will help it stay flat and square (make sure your jig forms a perfect right angle). Start with a coarse grit sandpaper between 100 and 150. The final sanding should be done with a grit between 320 and 600. Sand away material in small increments and check the height of the nut occasionally with the third fret method described above. If you sand away too much material you may have to replace the nut.

Once the nut is the proper height, clean up any excess glue where the nut was seated on the neck with a chisel, file or sandpaper wrapped around a small square block (if you don’t have much experience with a chisel, stick with the file or sandpaper). Make sure the nut’s seat stays square and flat. Place a small drop of hide glue or white glue on the nut’s seat. Place the nut in its seat and tune the instrument to pitch (the strings will act as a clamp). Make sure that the nut doesn’t wander while tensioning the strings. Wipe away excess glue with a moist paper towel and allow it to dry for about 12 hours before playing the instrument. You’ve just improved both the intonation and the action at the lower frets!

Maxed-Out Compensation and Instruments with Fixed Saddles

Some instruments’ saddles may be adjusted all the way back or forward but they still do not intonate correctly. Other instruments with incorrect intonation have fixed saddles so their compensation cannot be adjusted easily. The intonation of these instruments may be improved or corrected in one of the following ways, depending on action, relief and string tension.

In general, a guitar or bass with high action, excessive relief or lower-tension strings will require more compensation, as all these conditions require the strings to stretch further when fretted. Instruments with the saddles adjusted all the way back (or a fixed saddle) and sharp intonation may have their action lowered, relief reduced or higher-tension strings installed in an effort to correct their intonation. Conversely, instruments with saddles adjusted all the way forward (or a fixed saddle) and flat intonation may have their action raised, relief increased or lower-tension strings installed to improve or correct their intonation. If you are not familiar with adjusting action or relief on your own, consider taking your instrument to a luthier for these adjustments.

As always, thanks for reading. See you in a month!

Copyright © Anthony Olinger, Xylem Handmade Basses and Guitars 2009.