Time to fret!
I have to do a couple of things to prepare the fretboard for the frets. First is to make sure that the fretboard is perfectly flat. It was when I made it, but in gluing it onto the neck it's possible that a little hump has been introduced at the 14th fret neck/body joint. If the body and neck aren't perfectly in line with each other, then when the fretboard extension is glued to the body the clamping force will push it down a skosh. A little sanding will remove this skosh.
Then I have to radius the fretboard across the width. Different makers use different radii, but I like a 16' radius, which is what Martin uses. For me Martin is the standard and any deviation everything works off of that; so until I have enough experience to know what effect a deviation from the standard is going to have, I'm sticking with the standard.
I use a special sanding block with the 16' radius; yo ucan see here what a small amount of curve we're talking about. I draw a centerline down the fretboard, and start sanding with 100 grit paper.
When the centerline disappears all the way down the length I know the fretboard has been fully radiused. I then switch to 150 grit paper and finish with 220, which leave a nice smooth finish on the fretboard.
Fret wire comes in different sizes and different widths. There are two main components to a fret: the fret itself, which sits above the fretboard, and the tang, which fits into the slots that were sawn into the fretboard. A cross section of a fret would look like a T with the top rounded over. Along the length of the tang are barbs that grab hold of the sides of the fret slot and hold the fret in. Fretwire from LMI comes in a coil, which is convenient since the fretboard is domed. Other suppliers send the wire in straight sections--it's probably easier to mail like this--but then the curve has to be introduced. If not, the wire wants to spring back to it's original straight shape after being hammered in, and that's not a good thing.
I cut the fretwire for each fret first. Because the fretboard gets wider toward the body each piece is a different lenght, so I drilled some holes in a stick and numbered them to keep track.
The fret slots don't extend into the fretboard binding; this keeps the tang ends from being visible, but means that the tang needs to be removed where it goes over the binding. I have a special tool that nips the tang off the end, and then remove any burrs left with a file.
Every guitar is eventually going to need to have the frets replaced, and the danger in removing frets is that the barbs can chip the fretboard right at the slot. To help prevent this in the future I use a small triangular file to bevel the top of each slot.
Loose frets are never good, so as an added precaution I put a little Titebond wood glue on the tang before hammering it in. I use Titebond rather than epoxy or superglue because it loosens with some heat, so in removing the fret in the future it can be heated with a soldering iron before removing the fret. Here's the first fret hammered in, after I've wiped the glue squeeze-out with a damp paper towel.
Just to be sure the frets are seated properly I'll stop every once in a while and squeeze them in my vice.
The fretboard extension is a problem since hammering over this unsupported area can crack the top. First I widen the slots using a small piece of fretwire that's been bent 90 degrees. By running the tang through the slots the barbs scrape away some of the wood from the slots. Then I use more glue than in the other fret slots, lightly tap the fret into the slot just enough to hold it in place, and put the 16' radius block on top of the fret and clamp it down, using a caul inside the body like when I glued the fretboard on.
I do this for frets 16-20. (I can hammer the 14th and 15th fret because the heel block provided the mass needed to protect the top.)
Once all the frets are installed I check to make sure they are all well-seated. I then use some fret nippers to clip the ends as close to the fretboard as possible, and a file to finish the job so they are flush.
Oh, hey, I remembered I had a special fret file that I should have used. The edges are rounded so I don't have to worry about damaging the wood when I file the frets. I grab it and level the frets so they are even with each other.
This is an important step, because if a fret is higher than another one, then when a string is fretted just above the high one the vibrating string will hit the high fret. At best this will dampen the string, affecting both it's tone as well as its volume; but usually what will happen is an annoying buzzing that will drive anyone within listening distance to run from the room.
I have a piece of metal that has sides of different length. If when I place it across three frets it doesn't move, the three frets are even with each other, but if there is any rocking movement then I know that the middle fret is higher.
The different length sides are because the frets get progressively closer as you move down the fretboard (toward the body) and pretty soon I'm spanning four frets with the long side, and it's impossible to then identify the offending fret. I used to use my engineers square for this but it didn't work well for the last few frets. This little tool was worth the money.
OK, so now all the frets are level, but now instead of a nice round crown, the frets have a flat surface, so now I have to re-crown the frets.
This is done with another special tool with a concave filing surface.
Even though the sides of the file won't reach the fretboard I use a piece of thin metal with a slot for the fret to protect the fretboard in case I slip or something.
After the frets are crowned, the ends get beveled.
Then I remove the sharp burr from the ends and round each end so that the player's hand moves smoothly up and down the neck and doesn't encounter any sharp edges. This file is smooth on all but the two sides so I can use it without protecting the fretboard.
That's it for now. One of the last things I'll do before delivering the guitar is to sand the frets to remove the file marks, and then polish them to a nice shine. For now, it's time to prep the guitar for applying finish.