I've never been able to find detailed instructions on how to wind a coil. Might have overlooked it someplace but here's my recipe. No problem to make double-helix coil that fits easily into a 2" I.D. column - wound without any filler of any kind using 1/4" refrigeration tubing (0.030" wall thickness) and a piece of 3/4" PVC pipe as mandrel.
Instructions:
Wear thin leather gloves or you won't be able grasp it very well nor exert enough strength to roll the coil. Plus you'll get major blisters without gloves. Remember - the FIRST turn of the coil is the most difficult; the rest still require you to exhert a steady hard pull so you'll have to do small sections at a time.
1. Starting with the coil of tubing in floor in front of you and about 5' straightened out toward you . With mandrel across your lap - grasp the end of the tubing and hold about a foot to overlap the mandrel and at right angles to the mandrel (toward your crotch).
2. Hold the one-foot portion with your right hand (if RH) , left hand on the other side of the mandrel (away from you). Now pull in both (opposing) directions with all your might (as if you're trying to pull it in two!) and slowly-slowly just start to bend each side down and around the mandrel. Do NOT try to go over one-fourth or even one-fifth of the way around with this behemoth effort that you almost black out doing! 'Become one' with it and try to bend it like Uri Geller does spoons
3. Now that it is only slightly bent around the mandrel, stop and rest. Now repeat the above & take it to being nearly a third way around. Never stop pulling with all your strength. Rest again and repeat till it's over half way.
4. Now turn the whole thing over so the short end is sticking up in the air, switch hands and finish one revolution. I don't have to tell you to never stop pulling till you hallucinate!
5. Okay you're around but it's hard to hold onto for the next turn. Stand up, stretch your left leg way out with bent knee. Hold the mandrel with left hand on top of your knee and pull the other (long) end with right hand. You'll have to tighten the one turn up with only your left thumb since there's only one turn. At this stage you're using super wrist power to twist the mandrel while pulling your guts out with right hand.
6. Now 2 turns. Whew! Keep doing the same, only now you've *almost* enought to grasp the mandrel & coil with your left thumb and first two fingers wrapped around it. Your wrist will die and you'll be popping sweat beads! MUST maintain strong tension until you finish the coil or pass out first.
7. Remember to keep the turns fairly close, but not necessarily touching. Just don't get carried away. Make it as long as you need for this first layer then stop and take your time to study the return back up. Just keep pulling with right hand while rolling it on with twisting left wrist. Adust the return first coil nice and neat before going on to the second turn. Once this is done, you're home free to wrap it tightly over the first layer. The outer turns don't require near as much horsepower.
8. You made it back to the top (nearly dead by now, but happy). Now carefully wind on the the very last turn so that the two legs are parallel and cut it off to match the beginning leg. Fishished, and nice! Only very, very slight flattening; can't really even see any truthfully.
There may be easier ways and maybe this will inspire someone to post easier method. If you use salt as some suggest, then go right now and buy a $2 'waterhose-to-1/4" tubing' connector gizmo at Lowe's/Home Depot so that you can hook it to a waterhose when you're finished. Then wait for half hour or more (maybe much more) till it eventually blows out the salt. Trust me on this. You don't need salt.
Good luck,
Eth&All
Ok, here it is some what assembled.
Ok, here is the coil I made, before I pulled it apart a little so vapors could get around it. This is 20' of 1/4" copper tubing, I raped it around a 2" copper pipe.