I used two 4" Bessey Clamps. These can be found for under $4 ea. on occasion at Home Depot. It's a simple matter to grind off the dimples on the bars and separate the clamp screw arm from the rest. I also used a couple of 3-1/2" pieces of 1/4-20 allthread rod, two 1/4-20 wingnuts and a couple of 1/2" spacers. Mine are metal (because I had a bin full of them in my metalworking stuff) but wood or plastic would work as well. I cut a couple of pieces of hardwood as shown and drilled 3/16" holes for the threaded rod. It's easy to clamp onto the threaded rod with Vise-Grips and screw it into the hardwood blocks until flush with the bottom. The threaded rod will cut it's own way into the wood blocks. The wood blocks with the threaded rods are glued to the side of the jig as shown.
The slot in the Bessey clamp is a bit too small to fit over the threaded rod, so I drilled them out in the center of the slot using a 1/4" drill bit. I cut the clamp handles off just above the cove behind the metal ferrule. This is to help avoid overclamping, which could bend the threaded rod or split out the wood blocks they are mounted in. Finger tight is plenty good enough.
This design allows the clamps to swing out of the way when advancing the fretboard blank to cut the next slot.
