I never used a jig for crow calls. Did them more by eye and trial and error. I basically take two strips of wood about 3" long, x 1" x 1/2" thick and stick them together with double sided tape. This gives me a 1" x 1" rectangular piece. I chuck it about halfway into a Oneway chuck and turn the exposed portion round to a tapered 5/8" diameter. -I'll also turn some "O" ring grooves in this section [Latta style].
Next I'll drill a 1/4"diameter hole about 2-3/4" into the center of the turned portion. At this point I'll swap the piece end for end, and rechuck it. I'll finish turning the mouth portion to shape.
Now remove from the piece from the chuck and mark about a 1/16" line on each side of the center (pieces will still be joined with the double side tape) tape line. Now draw a "V" about 3/4" long, using the 1/16" lines as the wings, and extending it down to a point in the center of the call. -This will be the area that gets sanded away. Now separate the taped pieces. On a stationary belt sander, I will carefully sand this marked area away on both halves. They should intersect and slightly overlap the end of the stopped 1/4" hole. At this point I'll insert a 10 mil reed and give it a test for sound. If you don't get the sound desired, sand the taper alittle more to open up the air hole. -Look in from the mouth end of the call and observe how much reed is exposed and adjust accordingly.
That'll give you a start. After you make a few it will become second nature. Hope this helps.
Dave