I knew if I didn’t reshape the top of the saddle to match the fretboard, the D and G pairs would be radically higher than the other strings. This meant the saddle had a much more pronounced arch than the fretboard. The fretboard had a 14"radius ( Photo 2), but the bridge saddle was around 8".
My radius gauge revealed what I’d suspected-it wasn’t even close. My next step was to check if the saddle’s radius matched the fretboard radius. With these measurements in hand, I was ready to get to work. When I checked the intonation with a strobe tuner, and compared the 12th fret harmonics to their corresponding fretted notes, I found most of the fretted notes were from two to six cents sharp, although the G and D pairs were flat by about three cents. At this point, I knew my job would simply entail lowering the action at the bridge saddle. At the 1st fret, the 1st string was 1/64" and the 11th string was just over 2/64" above the fret. 012"-perfect for my client’s playing style. Here’s how the D-12-20 measured up: The action at the 12th fret was 6/64" for the 1st string and 7/64" for the 11th string. Repeat the process until you’ve documented the intonation at the 12th fret for all 12 strings. If the fretted note is sharp or flat compared to the reference harmonic, write down how many cents it’s off and in which direction. (Naturally, this is tricky on a 12-string because you have to pluck each individual string of the six pairs.) Starting with the 1st string, play the 12th-fret harmonic-make sure it’s in tune-and then fret the same note. Now remove the capo and check the action at the 1st fret.įinally, using a strobe tuner, check the intonation for each string. You can identify this gap by tapping the 11th and 12th strings against the frets while still pressing them down at the 14th fret. Typically this occurs around the middle of the fretboard, somewhere between the 7th and 9th frets. Next measure the relief: With the capo still on the 1st fret, hold the 11th and 12th strings down at the 14th fret and measure the greatest gap between the bottom of the 11th string and the top of the frets. Some electric 12s, notably Rickenbackers, reverse this order.) Measure the distance between the bottom of the string and the top of the 12th fret. (We’ll assume your 12-string has the standard octave-string configuration, i.e., the octaves in each pair are closer to you than their wound partners. Take this measurement for both the 1st and 11th strings-the first of the doubled high Es and the low E string. You’ll be taking several measurements, so write them down as you go.įirst, put a capo on the 1st fret and measure action at the 12th fret with a string action gauge. These specs provide a baseline to help gauge your progress. Before starting this kind of work on a guitar, it’s important to tune to concert pitch and take measurements.
You can estimate where each string should rest on the saddle, but it’s nearly impossible to get it perfect on the first try." You’ll also need a mechanical pencil, a capo, self-adhesive 80-grit and standard 400-grit sandpaper, and flat, single-cut miniature needle files. These include a string action gauge, radius gauges, and a radius block (the latter must match the fretboard radius). To intonate a 12-string, you need a few specialized luthier tools. I knew that once I completed these tasks, the D-12-20 would play better than ever and sound more in tune at the higher frets. My job was twofold: lower the action by reshaping the bridge saddle and then intonate each string. Somewhere along the line a previous owner or tech had installed a saddle that was both too high and incorrectly radiused ( Photo 1). Fortunately for the guitar’s current owner, the problem was rather simple. Many old 12-strings require a neck reset (an expensive proposition), but I checked the neck angle and it was fine. The guitar was in good shape when its owner brought it into the shop, but it didn’t play even remotely in tune and the action was uncomfortably high. We’ll use a beautiful 1972 Martin D-12-20 as our project guitar. Let’s investigate and see exactly what’s involved. Intonating a flattop 12-string with a straight bridge saddle involves filing unique break angle and intonation points for each string-an operation that requires skill and patience. But times have changed, and as music and recording technology have evolved, most musicians and producers expect a 12-string to play reasonably in tune all along the fretboard. In fact for many players, the slightly out-of-tune jangle was a big part of a 12-string’s aural mystique. Back in the day, it was rare to find an acoustic 12-string with a compensated bridge saddle. Intonating a flattop’s bridge saddle is tricky, and that’s especially true when it comes to vintage 12-string guitars.
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