Cutting the channels for the frets in the fretboard is a very detailed job. The slots have to be cut right on the money in order to avoid some intonation problems with the guitar. The easiest way to avoid problems is to develop aids to help you through this process. Some of these you can make yourself and others can be purchased.
If you are just making one or two guitars for yourself or friends, you can get by without the use of a fret channel cutting jig, but you will spend a lot of time in marking and laying out the fretboard in the process. You will also need to check and double-check each and every fret channel that you cut if you are being accurate. And yes, you may ruin a fretboard in the process.
For years, I used a jig that I make myself. It was a miter saw box with all of the fret slot cut into it. I would clamp the fretboard blank into the jig and saw away. It had removable scale templates too so you don’t have to make an entire miter box for additional scales, just the template portion of it.
Now I use a 6″ circular saw blade with a .023″ kerf, mounted in my table saw, combined with a couple of blade stabilizers to reinforce this really thin blade. I make my scales on 1/16″ acrylic that I cut on my CNC. This is mounted in a jig that holds both the fretboard and the fret scale template on the saw’s miter gauge. This has been a real time-saver for me as I can now cut the fret channels in about 5 minutes (after setup), with absolute accuracy.
Cutting the Channels:
To cut the channels or slots for the frets in the fretboard, it is easiest to mill the fretboard so it is the proper thickness. Also is you wait to taper the width of the fretboard, it will be easier to fit it in the jig.
Set your saw depth to be slightly deeper than the fret tang. This can be done by clamping a guide on the blade of the saw.
Screw or bolt the fretboard down to the jig and your setup is all done.
You can just slide the fretboard slider portion of the jig to each fret location and the saw is automatically guided in the exact fret-sawing position. Start with light strokes and use long eave cuts of the saw.
The Final Cuts:
When all the slots are cut, you can remove the cutting depth guide and cut the fretboard to length at the zero fret slot of the template and cut the fretboard to exact length.