Here is how I made a set of fitness rings using grey Sch 40 PVC conduit. I was inspired by this Instructable and various comments posted on it:
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
Unless you can find a 10-inch inner-diameter cylinder, you might need to calculate how long to cut your pipe rather than using my dimensions. Fortunately, there seems to be some room for error. If you cut it too big, you can squish the ends together and trim them once the pipe cools. This could deform the handles a bit. If you cut it too small, you may have trouble keeping the rings in a circular shape.
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
Tape one end of a pipe and fill it with sand. Tap the pipe on the ground to compact the sand. I used Gorilla tape which seemed to hold well and when it was later removed, it didn't leave a sticky residue behind. When you are done filling the pipe with sand, tape the other end. Repeat with the other pipe.
Step 4: Heat Pipe in Oven
My oven wasn't large enough to fit the pipe so I did performed the following steps for each pipe:
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.
Step 5: Remove Pipe From Oven and Place in Your Cylinder
There are two things to be careful of here: the hot pipe and the hot wire. Make sure you use gloves or towels (I used two towels). Remove the wire (with your gloves on) and quickly put the pipe into your cylindrical object. You probably want to make sure the bottom of your cylinder is smooth so it doesn't texture your pipe (though you could sand it later). Push the pipe down with the ends touching so that the pipe retains its circular shape. If your pipe is too small, you may need to put something on top of it, in the center, or just hold it in place with your gloved hands. Wait for about 5-10 minutes for the pipe to cool. (NOTE: this is a shiny metal trashcan so it reflects the ring -- I did one ring at a time)
Step 6: Empty Sand
Once the rings cool, remove the tape and empty out all of the sand.
Step 7: Trim the Ends
If your ends are squished, trim the squished parts off so you can insert the straps.
Step 8: Feed Strap Through Each Ring
Tape the end of the strap to a wire (I used a coat hanger) and feed it through the ring. Remove the tape and the wire.
Step 9: Find a Nice Place to Hang Them!
There, you're done! I didn't follow this step as I only have a pullup-bar at the moment (I'll find somewhere better to hang them). Though you could feed rope through the rings as in the other Gym ring Indestructible and then attach the lashing straps, I found that the rings are so rigid that just feeding in the straps works well (at least with my body weight). Kinking was never an issue. I had used plywood under my trashcan and pressed down hard on the left ring so there was a bit of plywood texture on it. I just sanded the texture off and used steel wool to make it smooth. If you want grippier rings, you can just add athletic tape or tennis-grip tape.