I looked at several commercial options to get a sense of the design and size of these chairs. This project morphed from a swinging bench so I wanted it to be big enough for 2 kids. It is going in my daughters room so it will be used for reading and play dates.
I looked at a few options for heating the tubes and went with hot sand since other methods are impractical for longer tubes. I bought a hot plate from the local thrift store and liberated some of the kids sandbox sand and was ready to start.
I managed to make the chair with 1 3/4"x10' tube, 4 1/2"x10' tubes. There are only 3 different types of fittings: 1/2",1/2",1/2" T's, 3/4",3/4",1/2" T's and 1/2" cross.
Step 1: Bending
PVC tubes from Home Depot come in 10' lengths so I figured the front outer circle would be just big enough for my needs if I bent 1 full length 3/4" tube. As a first try bending PVC maybe this wasn't the easiest choice.
I slid a cap on one end and used a small funnel to load sand into the tube. It takes 12-15 ladle-fulls and what I noticed was that the sand that traveled to the far end of the tube cooled off by the time it fell through the tube and then sat as I continued to fill the tube. The result is a not uniformly heated tube where one end is quite stiff and one is quite floppy. If you look up close at the outer circle, the bends on one side are a bit wonky.
I noticed this for the smaller and shorter tubes as well. The hot plate I was using had 400deg F as its hottest temp but it was old so who knows what temp it got to. I believe it would have worked a bit better in general with slightly hotter sand.
Next I bent several 1/2" pieces in a long-radius 90deg bend. I used some nails in a sheet of plywood to hold them as the cooled and make each of these tubes relatively the same shape. I cut these as needed and used them for most of the rest of the chair.
The 2nd step in construction was to cut the outer circle and install the fittings for the 3 full length vertical pieces. Then cut those to add cross pieces an so on util you see the final frame in the last pic. I dry fit the entire frame before gluing any of the pieces into the fittings. I did most of the cutting for fittings while the tube was in the frame. Friction fit, it mostly stayed together as I cut.
Step 2: Paint and Cushion
I spray painted the frame. It took 2 cans of spray paint to get enough coats on the tubes to cover the writing. A fai bit was lost as over spray since the tubes are thin.
I do not have a good picture of it, but I installed a plastic mesh in the area of the frame where the cushions rest. Even though I had 3" think "camping" foam, I thought there needed to be extra support so a hand or knee did not push through a space in the frame. My intention was to staple it in place but a hand construction stapler would not penetrate the plastic and my air compressor stapler blew the tube to pieces, I'm glad I tested this on an off-cut. I ended up sewing the mesh onto the frame. A make shift solution on which I would like to improve should I ever try this again.
I cut the cushions in 4 pieces to maintain the bowl-like shape of the chair. I used a fleece throw blanket to cover them, and used this as an excuse to buy a used sewing machine on Kijiji. I sewed a piece of webbing onto the inside of the top of the cushion covers and attached a button at the same spot on the outside. I cut the foam and bottom piece of the cover so the webbing could pass through and pull the cushion down onto the frame. The foam was rigid enough that it wanted to straighten out and lift off the frame. This way it keeps the round shape of the frame. I will add some detail pictures of this soon.
Step 3: Conclusion
In the end I spent 2 days bending and making the frame and another day cutting foam and sewing the cushions. Prior to that I spent quite a bit of time looking at designs and deciding how I wanted to do things so I was well prepared going in. I am quite satisfied with how it came together and the end product.
I just used some utility rope and an eye hook in the ceiling to hang the chair. Ultimately, it ended up in my daughters room. This was a temp location so she could try it out on christmas day.
At 180 lbs the chair can support my weight but, the way it bent, I don't think it is quite strong enough for me as a daily user. It will be plenty strong for 1 or 2 8 or 10 year old's and will hopefully last a few years. Using a combo of 1", 3/4" and 1/2" PVC, you could make one strong enough for an adult. Bending 1" tubes is probably the upper maximum of the hot sand method. Some trials would be in order before proceeding along those lines.