I purchased two plastic "squares" from Lowes and a section of Oak board 4" wide ( but it could be any width you need it to be). As you can see in the pics, I used the oak only to give the squares some space apart. Pretty straightforward, but just a couple notes. The end cuts on the board don't matter. I left small gaps at the ends where the boards come close to either end. That way, being slightly off on the cut won't hurt anything. You are relying on the squares to keep the form. All the boards have to do is be straight along their edges. When putting it together, I attached one side, then held it all together with clamps as I drilled and screwed the other side together (Note the level holding the ends parallel). Remember, the board should be offset slightly back from the end. I countersuckk the screws so the pieces would have less tendency to slip. You just have to make sure your holes are centered correectly or the screw will pull the piecec out of alignment as the head centers in the hole. Button head screws should work too as long as the hole is the exact diameter as the screw. Cost of this jig was about $14 dollars. See the wing rib logs for the jig in use.
