Rather than using regular PVC pipe, I decided to use grey conduit as it is designed to be bent when heated up. I also used fine-grained "play sand" because it can be compacted better than most sand you would find on the ground (unless you live at the beach), resulting in fewer air pockets and presumably a reduced chance of the pipe kinking. I have a small oven that is not large enough to fit the lengths of pipe so I describe the steps to compensate for that.
Overall, this process was much simpler than I had anticipated. Once all the materials were in-place, it only took me about an hour to actually make the rings and they seem very strong.
Step 1: Get Materials
2 x 27.5" sections of 1" diameter grey rigid schedule 40 PVC conduit (Home Depot)
2 x 12 foot lashing straps (Harbor Freight Tools $3.99)
wire (if your oven is small)
Gorilla Tape (or duct tape)
PVC pipe cutter (or hacksaw)
a 9.5-inch inner-diameter cylindrical object (like a bucket or a trashcan)
More information on bending and cutting PVC pipe can be found here:
Step 2: Determine How Long You Need to Cut Your Pipe
According to Wikipedia, dimensions for gymnastics rings are as follows:
Inside Diameter of the rings 18 cm (~7.06 inches)
Thickness of the rings 2.8 cm (~1.10 inches)
Total Diameter of the rings 23.6 cm (~9.29 inches) (thickness 2.8 cm, 18 + 2.8 * 2 = 23.6)
Depending on the diameter of your cylindrical object, however, your dimensions might vary. I used a metal trash can that has a 10-inch inner diameter so my dimensions were as follows:
Inside Diameter of the rings = 7.5 inches
Thickness of the rings = 1.25 inches
Total Diameter of the rings = 10 inches
I estimated the length of pipe I needed by calculating the circumference using the average of the inner and outer diameter of the rings, which is the circumference of the middle of the pipe:
average_diameter = (10 + 7.5) / 2 = 8.75
length = average_diameter * 3.1415
In retrospect, I probably should have used the circumference of the inner diameter of the rings so the ends wouldn't have to be squished together as much (this slightly deformed the rings, resulting in more oval-like hand holds).
Step 3: Fill Pipes With Sand and Cap
Step 4: Heat Pipe in Oven
1) heat for 5 minutes (other end was sticking out)
2) rotate pipe so other end is sticking out
3) heat for 5 minutes
4) bend pipe into horseshoe shape and keep the shape by using wire (I bent an old coat hanger). I could now close the oven door!
5) close oven door and heat for 5 minutes
Make sure you watch the pipe to make sure it doesn't turn brown! We want our cakes and breads to turn brown -- not our pipes. You may need to vary the temperature and keep an eye on it.