The two pieces of my criss cross are 3/4 thick, 2 1/4 wide and 18 inches long. I made pins out of bolts. They were long enough to cut the heads and threads off. My pins are 5/16th in dia. and it is because I had them on hand. Any size will work. I made them out of cheap bolts and I waxed them with paste floor wax. Brass will work but Stainless steel bolts even better.
Drill a hole in the center and lay out a 1/12 diameter circle in one end. The other end get a 2 1/4 circle laid out. Drill a hole at the center of the 1 1/2 in mark. All holes should be drilled with a drill press if possible to keep perpendicularity or do the best you can. The bottom of the chop at the end of the criss cross will stick out 3/8 inch more than the chop at the top. It has to do with fulcrum points and what clamps what, kind of like a titer tot. If you don't understand just have faith and you will when it is done.
The pin hole in the leg and chop is 10 1/2 inches down from the top of the bench and 3/4 from the front edge. I would strongly advise you to make a proto type as I did and you will see how it works. I glued some 2 x4 to make the leg and chop the gtove is 1 1/2 deep. You will understand how to radius the criss crosses. Actually the criss crosses were 1/12 wide with 3/4 radius cut on both at both ends for the proto type. Build out of\cheap stuff before starting for real.
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When you get this far put a clamp about 2 1/2 higher and clamp a board in your vise to see how it works.
I will give more information latter.