I am not sure if the term "double helix" applies but what I am basically trying to do is make a part representing a copper coil for a condenser. The copper coil is coiled along a length (say 4-5'') and when it reaches the bottom, flatten out and then coil back up the opposite way (inside of the outer coil,) with a smaller helix diameter. I have used the helix and spiral commands and created sweeps for the inner and outer coil but am having trouble with the flattened part at the bottom. If I try a regular sweep with a 3 point arc i get a "Zero thickness geometry" error, and can't seem to figure it out.

Thanks in advance for the help!