This is the first copper tube primary I ever made. I built it for the "improved" junk box coil. I used 1/4" soft refrigeration tubing mounted on an 18"x18" wooden table (recycled from the original junk box coil). The insulating supports are made from short pieces of 1/2" sch 40 PVC pipe drilled every 1/4" and glued to the tabletop with clear silicone cement.Here's how I marked the pipes in order to get a perfect spiral. Small plastic cable ties through the holes in the supports bind the copper tube tightly to the PVC supports. I thought the cable tie system would be ugly, but it actually looks pretty neat. In keeping with the spirit of the junk box coil, it was very cheap to build. It was also very easy --a child could have done it. It required no machining, notching, or precise fitting--just a ruler and a hand drill. The white circle in the center is a 4" plastic "test plug" cemented to the tabletop. The bottom of the 4" sch 40 PVC secondary form fits snugly over it for easy removal & replacement.