Now that we understand truss rods a little better, let’s move on to nuts, saddles and compensation… is that a band?
Nuts and saddles have been made of many things… plastic, ivory, bone and even mother of pearl. Of all these bone is the top choice. It’s easy to get, cheap and transmits sound very well.
Cutting the slots for strings in nuts is more complicated than it sounds. The spacing between the strings is not equal. Simply taking the space and dividing by the number of strings will give you a spacing that feels awkward to play. The thickness of the strings has to be taken into account. The thicker the string the more space. Lutherie tool shops such as Stewart MacDonald have rulers that will give you correct spacing if you don’t want to agonize over the math. While you can get away without this tool, the files to cut the slots are a must and they’re not cheap. In the smaller gauges they can be quite fragile as well, especially when you get to .010″.
I usually start by taking a .060 depth as my target and dial in individual preferences from there. If you do go too deep you can use some of the bone dust and cyanoacrylate glue to build it back up again but it will not last as long as pure bone. On customer’s guitars I just start with a new nut blank.
Making the saddle is a little easier. Martin uses a 3/32″ thick saddle but most makers (including myself) use one that’s an 1/8″ thick. This has the benefit of being stronger and gives more area for compensation (more on that later). The bottom of the saddle and the slot should be perfectly flat. This is critical for the nut as well. If both are not in direct contact your sound will suffer.
The top of the saddle should be the same as the radius of your fret board. Radius gauges are available but you can simply take a piece of card and trace the end of your fret board to get the radius.
Using files and sandpaper radius the top of the saddle. Don’t worry about the height yet, it should be high. String your guitar up and measure the height of the string at the 12th fret. It should measure 3/32″ from the top of the fret to the bottom of the string on the base side and about 4.5/64″ on the treble. If it’s higher (most likely) remove double the distance from the saddle. Example if you are a 1/64th high take 1/32″ off the bottom of the saddle.
Once the height is dialed in you can intonate the saddle. Every guitar has a scale length. Martin uses two, 25.4″ for Dreadnaughts etc and a shorter one for 00’s and 000’s. Scale length affects the sound to some extent. Shorter scales tend to be a little sweeter, longer scales more open and rich. Some fingerstyle guitarists prefer scales that are 26″ or more. The scale is measured from the beginning of the fret board to the saddle, theoretically anyway. The strings actually have to have a greater length to play in tune. This is because the string is not laying flat on the fret board but suspended above. The higher the string the more it needs to extend beyond the scale length. This is also true of string diameter. The bigger the string, the more it needs to be compensated. This is why steel string saddles are slanted at the bridge.
One of the tricks I like to use is to take a piece of the high E string (.009 to .012″) and place it under the string you wish to intonate so that it is in line with the saddle. Now pluck the string in open position and tuned to pitch, then fret the string on the12th fret. If the pitch of the fretted note is different you can move the piece of string forward or backward until it is. If the fretted note is sharp move the piece of string back, if flat move it forward. When you are satisfied, mark the position of the piece of string. Take the saddle out and use the files again to shape it. Don’t take it to a point but round it over so the string breaks over the saddle gently. Now your guitar should be in tune all the way up the fret board.
I do find that all this goes down a little better with a nice Chardonnay!