I thought I'd document my method for cutting fret slots. Disclaimer: This is how I do it. BE SAFE. Follow your tools' directions. I'm not responsible for your accidents or bad decisions. In fact, DON'T DO THIS.
Are we good now?
SoI started with a shopmade miter box and a Harbor Freight pull saw, as shown above. I actually like that other saw better as the back is reinforced. Anyhow, what you can't really see in that miter box is that there's the spine of a utility knife blade sticking up there. It's the same thickness as the saw kerf and registers the kerfs cut into the templates, above. Two of the templates I laid out with 12" digital calipers; one I made using an actual Martin fretboard and the method below, using the fretboard as the template and the template material as the workpiece. I hope that makes sense.
To make a fretboard I'd affix the fretboard blank to the BACK of the appropriate template, then slide the template down onto the knife blade, then make my cut with the saw. No depth stop, meaning some trial and error and tweaking to get the depths somewhere in the neighborhood of right.
Not ideal. So recently I ordered a Stewmac tablesaw blade ground to the right thickness for fretwire. It was expensive, but using the templates I made and a dedicated table saw sled, I can cut a fretboard relatively quickly.
That's the bottom of the sled. I used a couple of those Microjig runners I had. They're great, but you don't need them. That saw blade's only 6" in diameter, as you can see, and it burns readily.
There's the sled, shown from the far side of the table saw. As you can see, I went with the utility knife again to register the template. It works a lot like a box joint jig, but you need to pay attention to your zero fret location. I used the end of the template when I made mine, but you'd be better off making it a slot and either using a zero fret (I've never done this) or cutting it off at that point. You'll figure it out.
In this configuration I glue the template on its side to the back of the fretboard blank. The knife is raised up in the registration slot so that the fretboard material sits under it.
Here's the view from the user's perspective. The template is taped to the walnut fretboard. To cut, you line the kerf in the template up with the utility knife blade (it's in the little slot to the left in the greenish poplar piece; the slot next to it is where the blade actually cuts. So you just work your way from one end of the template to the other, and it goes very quickly. Just remember that the slot depth equals the height of the blade sticking up past the bed of the sled (I used 1/4" tempered hardboard). Also remember that the blade is going to come out the back of your sled ... BE CAREFUL. All the slots are uniform, you only have to measure once, and you're moving on in minutes.
I hope this helps somebody. I didn't invent any of this; at most I adapted it from the video on the Stewmac site since I wanted to use my own templates and not pay for theirs, which are surely more accurate than my handmade ones.