New Primary Coil
This is the primary I built for my new 6-inch Tesla coil. It has 9 turns of 3/8th inch diameter soft refrigeration tubing wound in a flat spiral, with 3/8ths of an inch between turns. Inside diameter is 9 inches, OD is just under 24 inches. The coil is held in place with 108 plastic cable ties, two per turn, which pass over each turn and then cinch tightly underneath the plywood disk. I have the coil sitting up on six short pieces of 3/4th inch PVC pipe acting as insulators.
This is a super simple method for winding a flat spiral primary, which yields a very sturdy finished product. It requires no machining, notching, or precise fitting. I used only common hand tools. A child could do this. The main drawback is the tedious chore of lacing and cinching all those cable ties--it was rather time consuming.
Many coilers report all sorts of nightmare tales about primary construction, including kinks in the copper hose, turns that pop loose and won't stay put, plastics that are impossible to glue, cut fingers, etc., etc. My story is the opposite. This chore was so straightforward it was almost boring.
Originally I had planned to use 8 turns. I added the 9th turn at the last minute because I figured out that it would just barely fit on the precut 24-inch plywood circle without hanging off the edge. Now I have an extra turn to play with, but I have no room for a strike rail. I may run without one at first just to see how it goes. If I get a lot of primary strikes, I'll have to figure out how to squeeze a strike rail onto the outer edge.