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While the banjo may often find itself as the subject for numerous musical jokes, the modern banjo is a complex and carefully designed instrument. Just as with a violin, there are numerous variables in the banjo's construction and set up that can have great impact on its tone, projection, and playability. One of the unique features of the 5 string banjo (what is commonly thought of and seen when the word "banjo" is mentioned, although there are many different types of banjo) is the addition and positioning of the 5th string. This string begins midway down the neck of the instrument (typically on the 5th fret, or on the 8th fret of a long-scale "Seeger" instrument), causing fingerboard of the banjo to have a unique change in width to accomodate it. Usually, there is a special tuning machine for the 5th string at this point as well, jutting out on the thumb side of the neck. As would be expected, the 5th string also must have its own small "nut", seperate from the main nut up at the headstock that the other four strings pass over.
This extra nut, and how it is executed, can be problematic. The nut must be compact enough to fit on the small fingerboard jut near the 5th fret, but also strong enough to withstand the lateral force of the string being plucked. The nut must be "tall" enough to hold the string in place laterally when being played, but not so tall that it interferes with the player's thumb.
The style and construction of the nut can also be a hotbead for buzzing and rattling sounds if not properly installed, especially if it is set up behind the 5th fret. To compensate for this issue, some banjos are designed with the 5th string nut sitting right in line with the 5th string fret, so the 5th string does not pass over the 5th fret but is positively stopped at that position. This allows the 5th string to positively tune with the other 4 strings at the 5th fret position when played up the neck, eliminates the possibility of the 5th string rattling against the 5th fret when played as an open string, and allows the luthier to dial in a string height more akin to the height of the other four strings.
This banjo, a very nicely made Prucha, suffered from a broken 5th string nut. The nut material installed was a type of mildly dense plastic. I decided to fit a new nut made from bone, as the material is more dense and hard-wearing, and will also help with the tone of the string.
I ordered in a bone nut "blank" in the form on a long stick of bone, turned down to a 5mm cylinder. The nut itself on this banjo was particularly tiny, perhaps only slightly more than half of this diameter (which likely contributed to its breakage). For strength, I wanted to make the new nut slightly larger in diameter than the old one, but not nearly as massive as the blank. I cleaned up the hole the nut pip sat in, enlarging it to just over 3mm. I then chucked a piece of the nut "blank" into the drill press, and using a file and calipers, "turned" it down to the proper diameter with a very slight taper to seat in the hole. I then slotted the nut, trimmed it to height, and domed and polished the surface.
The tone of the 5th string is bright and crisp, and the string is easy to play. The player was very happy with the result, and I hope it gives him many, many years of trouble-free use and happy picking.
Prucha Banjo 5th String Nut
Prucha Banjo 5th String Nut
Click picture for more detail
Click picture for more detail