I started with blanks custom rounted from solid wood, there's a CNC supplier in Texas that does the work for me. The interior pockets have to line up exactly (we're talking 1/64") so the high precision CNC equipment does an excellent job. This run was five Cherry, five Mahogany and eight Walnut - Walnut being the one I run out of most often.
The first step is to cut the slots in the ends of the case, this is done using a jig and a dual combination miter saw (rotates to both plus and minus 45 degrees). The cuts are made from the inside of the open case, although it is still in two pieces. To create an X for each dart when the two pieces are put back together, that's 12 cuts per case so the jig comes in pretty handy. Because of the circular shape of the blade and the position of the jig, the angle at the end of the cut matches the bottom angle of a standard dart flight.
The next step is to route a slot for the hinges, a router table with a straight bit works well for this. Again, a jig is used to cut the right depth and width groove. Two cuts per case, one for each side. When placed together a 3/4" x 4" brass piano hinge fits exactly into the combined groove.
Then it's a matter of sanding and finishing. A belt sander works great for the front and the back but the rest must be sanded by hand, especially the edges of the grooves cut in the previous step. A 'green scrubby pad' works well for this - and is much less messy than steel wool. I then dip each side of each case completely in tung oil (a type of varnish), rub it in with a cotton cloth and put it in the rack to dry.
Thus ends the first day of dart case building, more to follow.