A New Nut
A 1940 Martin 000-28 gets A New Nut
I'd like to show you my general process in actually making a replacement nut. Of course, I can't go into all the details of fitting a new nut because there are so many possible difficulties that can crop up, especially with older instruments. As a repairman, my goal is to be anonymous, so I rarely change the style from that of the original manufacture.
This old 000-28 has been refretted a few times, and the nut has been recut, shimmed, and recut again. I have nothing against shimming a nut, but if the shims are too thick, they don't help the appearance at all! So, this nut replacement job is a matter of improving appearance. The original nut is ivory, which I'm replacing with bone, which, besides being politically correct, is also harder and more durable.
I like to make a small cut just behind the nut so that the peghead veneer or finish won't be damaged when I remove the old nut.
With the finest X-acto saw blade, I cut through the veneer, using my left thumb to hole the blade firmly against the back side of the nut. This little cut is only .010" wide, and is unnoticeable after the nut is replaced.
Now, all I have to do is tap the nut sharply with a hammer and a small protective block of wood to dislodge it.
It doesn't matter how tightly it's glued in place because no glue sticks all that well to nut material, or the end grain of the fingerboard. The nut always pops right out neatly.
I'll want to make my new nut the same size as the original, so I'll measure the thickness of the blank I'll need, making sure the flat front surface of the nut is held against the jaw of my caliper.
Actually, I really don't read the dial. I just lock the jaws and use the caliper as a "go-no-go" gauge and trial fit the nut blank as I adjust its thickness.
My favorite nut blank flattening and shaping device is an old marble cutting board to which I've clipped a sheet of 150 grit sandpaper.
By rubbing the bone nut blank on a new sheet of 150 grit, you'd be surprised how quickly I can flatten and shape it.
By the way, if I can't locate my caliper, I'll sometimes use an adjustable wrench.
As a quick gauge, it works almost as well as the real thing!
Once I have the nut blank flattened and reduced to the proper thickness, it's time to establish the bottom surface. On Martin guitars made before 1999 the bottom surface is in the same plane as the peghead. Most other guitars, including many recent Martin models, have the bottom surface on the same plane as the fingerboard. Lots of guitars have been altered slightly with replacement nuts and may have the bottom surface of the nut slot at an unusual angle.
I'll hold the nut at an approximate angle and rub it on my flat sandpaper plate.
I could spend some time and make a little fixture to establish this angle, but I find it quick and easy to do it freehand, simply comparing it against the original nut.
The key to comparing the angles is to hold the flat surfaces against a straightedge, and slide the new rectangular blank up against the bottom of the original nut.
This may seem tedious, but it rarely takes more than a minute or so. At this point the new blank should fit right in place, because the width is right, and the bottom is cut to the proper angle.
Let me get back to my sandpaper plate again, and introduce you to my special marking pencil.
This is a very simple little tool I keep around for marking nut height. I give it a few strokes against the sandpaper plate to clean and sharpen it.
Notice the pencil isn't really sanded halfway through, except at the point.
The point is rather fragile, but being flat on one side, it gives me an incredibly sharp marking line right against any surface.
Here, I'm using the half pencil, holding it against the tops of the frets to mark the projected line of the fret tops against the nut blank as I hold it in place.
The idea is to establish a minimum height line. The lowest string position in a nut is logically the same height as a fret, so I think of the top of my pencil line as a preliminary bottom line for string notches in the nut. That way I have the thickness of the pencil line as a "safety margin."
Here's my nut blank with the perimeter marked all around.
I like to use my little 1"x42" stationery belt sander to rough out the blank.
I'll sand about halfway through the pencil lines around the ends, but I'll leave extra material above my height line.
If the sander isn't available, a coarse double cut file works well as a roughing tool.
I have the ends trimmed, and sanded with 280 grit to fit precisely, but I've left the profile very rough, angular and oversize.
With the nut lightly glued in place, I'll mark the string positions on the top front edge.
I'll copy the original string spacing using the old nut, unless there's a reason to make a change.
Some players like the strings closer or farther from the edge, or the old nut may have had uneven spacing. In either case, I'll determine the location of the two outside strings, and then fill in the other four, spacing them evenly across the nut. Generally, you can't feel tiny differences in spacing when you play, but if you see that the spacing is uneven, you'll tend to focus on that, and then you will have some difficulty fretting. I try to space the strings so that there is an equal amount of distance between them, rather than space the centers of the strings at equal distances. This is a small point, and mostly a matter of cosmetics, in my opinion.
Once I have the pencil lines where I want them, I'll make a tiny little notch in the center of each one.
I'm using my sharpest file, and making just enough of a notch to balance the string in position so I can string the guitar and tune up.
With the guitar strung and tuned, I can now notch each string to the proper height, using an assortment of round edge nut files.
Look how I'm holding the file. I file the string slot at an angle that's halfway between the plane of the fingerboard and that of the peghead. That way, the string will rest in the entire length of the nut, and will bear right at the front edge as it exits toward the bridge. This is important stuff, because the string would buzz and play out of tune if it didn't bear on the front edge of the nut. I want the string to bear evenly through the length of the slot so that the nut won't wear out prematurely from friction as the string is tuned.
The shape of bottom of the slot is important, too. It should be rounded like the cross section of the string, and just wide enough so the string draws through it smoothly. If the slot were too tight, or V-shaped, the string would be pinched, tuning would be a nightmare, and the nut would wear out quickly.
Now, with all that in mind, I have a great opportunity to "dial in" the lateral positions of the strings as I file the nut notches to their optimum depth. Especially with the bass strings, I can rock the file to the side to allow the strings to settle in just the right positions. That's why my original notches were so tiny before I strung up the guitar.
OK, let's get back to work.
I keep the guitar tuned to pitch as I work, and I just lift each string out of its notch and let it slip aside so I can file its slot.
In order to get the height of each string slot just right, I need to check my progress often. I do that by mashing the string down between the second and third frets. Then I look closely under the string at the first fret to check its clearance.
Tuned to pitch, the string strikes a straight line from the nut, over the first fret, right to the second. I keep on filing the slot lower until the string just barely clears the first fret.
Here's my nut all set up.
The sides, bottom, and ends are fitted, and the string height is just right. Now all that's left is to make it look nice.
Working by hand, I'll smooth out my file and sanding marks using successively finer grits of sandpaper.
I'm also cutting the top of the nut profile lower, so that the strings won't appear "buried" in their slots. Most luthiers agree that the best looking nut has a portion of the string protruding above the height of the nut material. By filing the slots to the correct depth first, I have no problem in achieving the ideal finished look.
In the photo above, I'm using Micro Mesh abrasive cloth to polish the nut to a high shine, but I could also use my buffing wheel.
I try not to use power buffing to smooth out heavy scratches, because the wheel will tend to round the upper corners of the slots. It does a great job as a final finishing step though.
Well, done at last.
I have a nice shine here, and the strings fit just the way I like 'em. The wound strings stick up about 1/3, and the two steel strings sit just below the surface. I try not to let the unwound strings ride too high above the surface because they can sometimes jump out of their little notches if a capo gets pulled off center a bit.
Here are a couple more shots of the finished product.
