Step 7: The 2nd jig
It is made of 1/8 x 1/2 inch strap iron. One piece 4 1/2 inches long is the main part. Two wings 2 1/8 inch long each are welded to it at 90 degrees to make an "X." (One of my wings is not quite 90 degrees to the main piece. So, I had to add scoring marks on all four arms to define the exact position for the nails before welding. Some of the scoring marks are visible.)
I also added a round rod post to the underside of the jig so I can clamp it in the vise easily.
I bent the arms upward just a little so the finished welded cross would be flat. There is a square of aluminum at the center to prevent accidentally welding the tips of the nails to the jig. The aluminum is from an old automobile license plate.