Making A Bone String Nut
The string nut is a vital part of any stringed instrument. It sets the spacing of the strings across the neck and holds them at the proper distance above the fingerboard. If the nut is not working correctly, a whole host of problems can occur.
The nut can be made of many different materials. When replacing one, we have to consider a number of factors. Sometimes a prefabricated one can be shaped and fit to an instrument. However, if the desired sizing and material is unavailable, one must be cut by hand. We have written in greater detail about the different materials available in our previous blog post: string nuts. For this article, we will be focusing on the process of hand cutting a new string nut out of bone.
Replacing a String-Nut
This Gibson acoustic guitar recently came into the shop with the edge chipped off of the nut. As a result, the 1st string was no longer able to be held in position and would simply roll off of the edge of the fingerboard. There was no way around it, this nut needed to be replaced. What follows is basic outline of the work involved in replacing the damaged nut with one hand-cut from bone.
Removing the nut and cleaning the slot
Before a new nut can be installed, the original must be removed and the slot cleaned and prepped. To remove the original, we start by gently scoring the edges with a razor blade. This helps to prevent any finish from chipping out when the nut is removed.
Next we will use a small block pressed against the nut and a couple of gentle hammer taps to loosen. Often times, this alone is enough to free the nut. If required, we may use a pair of end nippers to gently pull it out after loosening. On rare occasions, if the nut has been too aggressively adhered, removal may require cutting the nut in half and/or chiseling it out. Fortunately this one came out before I even thought to take a photo.
Once free, we use a sharp chisel and a file to remove glue residue and clean up the slot. It is important that the slot be true and square, otherwise the new nut will not sit properly.
Shaping a nut blank
The original nut on this guitar was made of some type of synthetic material. We chose to replace it with a piece of unbleached bone because of its higher durability, and we liked how the aged look matched this vintage instrument.
Using a pencil, we sketched the outline of the old nut onto the blank. Then we took the blank over to the band saw, followed by the belt sander, to remove the bulk from the top and the sides. Next we trued up the bottom and the edge that will rest against the fretboard using sandpaper on the stone block pictured above.
It is extremely important that these be square in order to ensure a proper fit. Once this is finished, a micrometer is used to measure the width of the original. We can then use that measurement as a reference as we sand down the blank to the correct thickness. The blank will now fit nice and snug into the slot and is ready to be slotted.
Marking the String Spacing and Slotting
Once the blank is cut to shape, we are ready to begin slotting. To start, we mark our outer strings about 1/8″ in from the edge of the fingerboard. This leaves enough room to avoid pulling the strings off of the edge while playing. Next, using a special string spacing ruler, we are able to accurately mark the remaining string positions. This tool is crucial to ensure the strings fall in the right place and feel natural under the players fingers.
Now that the slot positions have been marked, we are ready to begin cutting them. To do this, we use gauged nut slotting files. These files are available in various sizes to fit different string gauges, and leave a rounded bottom for the string to sit in. They cut quick, and it is easy to go too far here. To avoid wrecking it, we work slow and check the depth often using a string as a guide.
Polishing and Installation
Once the slots have been cut to their final depth, it is time for final polishing. To start, we will smooth out the slots with abrasive cord. This is to make sure the string can slide easily through without hanging up and falling out of tune. Then we will do a final shaping of the nut: removing any excess material from the top, finalizing the rounded profile of the back, and rounding off the sharp edges of the top.
With that complete, we set to work bringing the nut up to a high polish. To do this, we use 600 grit sand paper to remove any coarse sanding or tooling marks before switching to higher grits for polishing. To finish the nut, we use a buffing wheel and compound to achieve a high gloss and professional look.
Once the nut is done, we tack it in place using a couple of drops of wood glue. We like wood glue for this job because is is strong enough to hold the nut in place but, in the event the nut ever needs to be replaced, it removes easily and does not leave a lot of residue to be cleaned up. After a setup, this guitar will be ready to return to making music.
About Guitar Repair Long Island:
Guitar Repair Long Island is the area’s premier destination for fretted musical instrument care and maintenance. We fix all fretted instruments, including: guitars, basses, banjos, mandolins, and ukuleles. Conveniently located in Ronkonkoma NY, the shop is dedicated to providing quick, honest, and reliable service. Our vast experience in all aspects of instrument repair ensures that we can help with whatever your needs are. Contact us or book your appointment today