Next, remove the capo (it wouldn’t hurt to confirm your strings are still at pitch) and measure the height of the 1st and 6th strings at the 1st fret (Photo 4).
In this case, the height was 1/64" and 2/64" for the 1st and 6th strings, respectively. While this is ideal for fretting chords and lines, it’s too low for playing slide.
From these preliminary measurements, I was able to determine what would be required to give this Les Paul its new dual identity:
• Raise the action at the bridge and then adjust individual saddles.
• Raise the action at the nut by either shimming the stock nut or carving a new one.
• Adjust the pickups to balance string-to-string volume.
• Adjust the intonation.
Adjust the bridge. To raise the action on a Les Paul’s Tune-o-matic bridge, turn the thumbwheels counter-clockwise (Photo 5). Do this in small increments, perhaps a quarter of a rotation for each thumbwheel. Retune the guitar, put a capo on the 1st fret, and then measure the action at the 12th fret again.
For starters, I suggest adjusting the action to 4/64" on both the 1st and 6th strings. Remember, you can always come back and raise the treble or bass strings a bit more if you find your slide is hitting the frets.
Adjust the saddles. Now here’s our first tricky part. Most lightweight slides (such as a glass or chrome tube, or the medicine bottle favored by Allman and Trucks) contact the strings in a straight line. However, on a guitar set up for fretting—including my client’s LP—the strings follow the fretboard radius or curvature. In other words, strings 1 through 6 are subtly arched at the bridge so they sit at a consistent height above the frets.
Slide licks often incorporate two or three strings at a time. When your slide has a straight playing surface, yet the strings are arched, you’ll wind up pressing some strings down more than others as you move across the fretboard. This can create subtle intonation problems within a chord or interval.
The solution is to flatten the string radius at the bridge so the strings sit in a straight line that corresponds to the slide’s playing surface. On a guitar with individually adjustable saddles, like a Strat, it’s easy to raise or lower each string to achieve the target 4/64" gap between the bottom of all the strings and the top of the 12th fret.
However, on a guitar with a fixed-radius bridge—such as a Les Paul with a Tune-o-matic—some saddle slots will need to be deepened slightly to create a flat line between strings 1 and 6. Typically it’s the middle saddles that need attention, but your current bridge radius and string gauges will determine which slots require recutting and by how much.
Gauged nut slotting files, which are available from Allparts, Stewart-MacDonald, and other luthier suppliers, work great for this task because you can precisely size the slot to match the string. For example, knowing that my client plays a .010–.046 set, I’ll use a .036 gauge nut file to deepen the notch for the .036 A string.
The process is pretty straightforward: After you’ve set the bridge so the 1st and 6th strings are 4/64" above the 12th fret, measure the 2nd string. If it’s also 4/64" at the 12th fret, move onto the 3rd string. But if it’s higher, carefully deepen the slot to bring the 2nd string down to 4/64".
When re-cutting a notch, always follow the angle of the string as it emerges from the tailpiece up to the saddle (Photo 6). Go slowly, retuning and then measuring the action every few file strokes. Gently clean off any burrs on the front or back of the saddle using the nut file. This will prevent the string from getting caught up on the saddle and creating tuning issues.
Repeat the process on each inside string until you’ve achieved a uniformly level playing surface across all six strings. It’s painstaking work, but the payoff in tone and feel will be worth the effort. Once you’ve flattened the radius and are satisfied with the overall action, you’ll be ready to move over to the nut.
Raise the nut. From experience, I knew that having the 1st string sit 1/64" above the 1st fret is too low for slide, so I’d need to raise the nut on this Les Paul. The trick, of course, is to get the nut high enough to accommodate slide technique, yet not make the guitar unplayable when fretting. Based on the owner’s playing style, string gauges, and light glass slide, I decided on a uniform height of 2/64" for all six strings on his guitar.
There are only two ways to correctly and permanently raise the nut: You can shim it or carve a new one. The owner wanted to keep the stock Gibson nut, which was in excellent condition, so we elected to shim it.