This is the fifth in the series of the Guitar Nut. If you have not read the first 4 articles, please read them to become familiarized with materials and initial shaping and fitting techniques that are required.
Tools and Materials:
Xacto Razor Saw
Gaged Nut Files
Woodworkers Marking Knife
Incra Steel Ruler
Marking the String Slot Locations:
Place the shaped nut into the nut channel and glue it into place if it does not fit tightly enough. To glue take a small amount of Duco Cement and place it on the backside of the nut and push it firmly against the fretboard. Hold in place with a strip of masking tape.
Now measure the distance between these 2 tick marks with the Digital Vernier Calipers. Get a reading of this distance and divide it by 5, which represents 5 string spaces BETWEEN the marks.
Set your calipers to the result of this number and evenly divide the nut with additional tick marks – once at each string.
GLS Tip #1: Let’s take an example. First determine the inset distance from the edge of the neck to the center line of the 2 outside strings. A good starter dimension is 3 – 3.5mm. This will be determined by the guitarists preferences. Let’s say it is 3mm.
Now measure the neck width at the nut. It measures 44mm. Subtract the 3mm + 3mm from the 44 and you have 38mm between the outside strings. Now divide 38mm by 5 and the result is 7.6mm spacing from center to center of all strings.
Marking the String Angles:
Next we have to mark the string angle from the backside of the nut to each respective tuning machine post. Hold your steel rule on each tick mark and place the other end of the ruler at a point where the string would start to wrap around each tuning machine post.
Take a very sharp lead pencil or a marking knife and mark this line exactly on the top of the nut.
Cut The Starter Slots:
Now take the Xacto Razor Saw and hold your metal ruler as a guide to cut each slot at the proper horizontal angle. Also be very careful as to the proper vertical angle that you are cutting. The object of the slot it that the string will rest on the very back of the nut (the point where the nut and fretboard join). If you can’t cut the exact vertical angle it is better to have the nut slot slant slightly downward toward the guitar headpiece.
Cut all of these slots in the same manner and make your cutting depth the exact depth to match the enhanced string depth slots on the backside of the nut. Once you have cut all the starter slots, it is time to cut the final slots.
Filing the Final Slot Depths:
Unquestionably the best method to cut in the final string slots is to use a set of Gaged Nut Files. These are available from StewMac and they work really well. They are quite expensive though and you may decide on an alternative method if you are only building a single guitar.
Select each file based of the string gages you intend on using.
To cut the final depth of nut slots, I prefer to use a Feeler Gage as a file stop. Place the gage flat on the fretboard right up against the backside of the nut.
How To Determine String Clearance:
This is based again on personal taste of each individual guitar player, so we will just discuss some average dimension here.
While you certainly could file the string slots down to the same height as a fret crown, most nuts take into account some extra string vibration and place the slots up just a bit. A good starting point is to increase the string height about 0.010″ on the treble side and 0.020″ on the bass side. The strings in-between these 2 outside strings would be graduated proportionally in depth.
Getting the Proper Feeler Gage Thickness:
To get the proper stack height for your feeler gage, bridge a straight edge (like a fret rocker) over 2 consecutive frets and measure the crown height with the feeler gage. Now add the proper string clearance discussed above and you are ready to file.
Be extremely careful here as this is when most nuts are ruined. Check and double check your angles. Many luthiers choose to have the guitar strung up at this point and actually slide the string in and out of the string slot to verify the channel depth and angle.
Carefully file down until you hit the top of the feeler gage stack for each string. Be sure to make your adjustments as you progress for bass string clearances.