An earlier post noted the importance of defining the scale length of the guitar before you begin. Setting the bridge exactly in relation to the nut is one of the last steps in building the guitar. But for it all to work, correctly, your frets must also be positioned perfectly.
There are a number of sites that have electronic calculators that will provide your fret spacing based on your chosen scale length (I used www.Stewmac.com). However, Stewmac also has the choice of great fret ruler. Even for a single guitar, I opted to spend the $29.95 due to the critical need for proper spacing. In addition, I had purchased a custom inlayed fret board… I just could’nt handle the thought of screwing up the effort the craftsman put into the inlay!
With the Fret Scale Rule marking my frets was easy enough with a sharpened marking knife. Cutting them was the next step likely to result in catastrophic error. Whenever accuracy or consistent repeatable results are necessary the best method is alway standardization.
I build my own fret slot miter box. It is simply made with a piece of squared and true quality plywood to serve as the base. I attached the fret board, centered and parallel with the sides. Over this I place an easily built carriage/saw guide. Looking at the picture you can see the top of the saw guide is two layered pieces of plywood to provide an ample face against the saw. On both edges of the guide is mounted a side that fits squarely and flush with the sides of the base.
(Note the center line, and the scale rule to the right)
The carriage/saw guide is then positioned over each fret mark and clamped securely in place. Placing the fret saw against the face of the guide and holding it flush with my left hand, I slowly begin cutting.
To control the depth I used a piece of card stock. Placing a piece of fret wire against the edge I measured the depth of the tang and marked the card slot. I would then periodically insert the card stock into the fret slot being cut to ensure consistent and even depth.
