The build wasn't too bad, but also not without its moments. The copper tubing I used was 3/4" "soft" tubing such that is used in air conditioning systems. I envisioned something akin to refrigerator ice maker tubing. Turns out it was not quite that easy. I can't remember the last time I cussed so much over a garage project.
Hey jackson; sounds like you are on a good path.
I have had to make many coils out of copper tubing, large and small diameter, in both professional and hobby builds. You are right; even for large coils it is not as easy as it appears. Copper will work harden - become more brittle - as it is mechanically deformed, and this can complicate forming a coil. Manufacturers may say that the tubing is supplied in a "dead soft" state, but YMMV. I have found the following steps to be quite useful. In the event you need to make new coils, the following may help.
1) Uncoil the roll to a somewhat straight length a bit longer than needed. It does not need to be perfectly straight, but there should be no kinks.
2) Torch the tubing (ox-acetylene preferred but "MAPP" or propane OK) by working a torch slowly down the tubing from one end to the other in a dimly lit room. You would like to bring the copper to a dull red color if possible, and keep it at that temp for maybe 10 seconds at each part of the tubing. This will help to soften the tubing a bit. When done, you would like to see a nice dark oxide film on the tube's surface.
3) When you have torched the entire length, let it air cool until you can handle it.
4) Fill the tubing with dry sand, closing the ends up with tape. For larger diameter tubing, this really goes a long way in preventing kinks.
5) Bend the tubing to shape. I generally bend against a form made from scrap plywood cut with a sabre saw. I generally bend "against" any remaining curvature in the tubing.
6) Remove the sand, and trim the ends to length. The oxide will need to be removed at points of electrical connection. You can leave it on the rest of the tubing, as it will act as a pretty good primer for paint top coats.
Looking forward to your tests!