Here's what I used.
- .25 inch Copper pipe. 5 feet long
- 1/4 cup of Salt. (Fine, dry Sand would also work)
- Funnel (or makeshift funnel)
- Hard Cylindrical Objects of various diameters. I used a 3" diameter steel pipe and a 1.5" diameter socket-wrench socket.
Step 1: Fill It With Salt
- Your tubing probably came as a coil, so straighten it out to begin. Use a flat surface like a table and roll the coil while holding one end on the table.
- Stand the tube upright and use some tape to cover the bottom hole.
- Use a funnel or other tool to pour the salt into the tube. Fill it all the way to the top.
- Help the salt settle by tapping the tube on the ground.
- Refill with salt until it can't settle any more.
- Cover the top hole with tape.
Step 2: Bend Using a Cylindrical Object
- Begin by bending your tubing into a much bigger circle than you want to end up with.
- Clamp your cylindrical object in the vice and, by hand, gently wrap the big coils down to coil around the cilinder. Sometimes a twisting motion can be useful, turning one end of your coil clockwise and the other counter-clockwise.
- Tap the tubing with a hammer (while it's on your cylinder) to help it reach an oval-shaped cross-section. This lets it stay happy even when making tight coils.
- Continue the process with smaller and smaller cylinders until you are at the size you desire.
For more advice on bending tubing, check out this article.
If you're curious about the Solar Parabolic Water Heater, check out the instructable.