I bent the 180 degree bend by inserting a coil extension spring (it was a perfect fit on the I.D.) and then bending it around another pipe. The spring follows the bend perfecting and keeps it round and with a rope tied to the loop at the end of the coil spring, it allows you to pull the spring out after its bent.
I did the 360 degree bend by capping both ends after filling the pipe with washed sandbox sand. I saw a bit of flattening when using sand but I could have avoided that by using a form rather than bending it around a piece of 3". I went tighter and further than I will need to for this upcoming project just to test my capabilities so I am confident I can eliminate the oval flattening (even though its not needed).
For 45 and 90 degree bends, the spring is the better and easier option. for bending a coil or hoops the sand is the better option.
If I need to make a bend in a long piece where the bend is far from the end, I would press a foam plug in from when end with a ram rod and then fill with sand and then another foam plug rammed in from the other end. I would make the bend and when cooled, pour acetone into the pipe to dissolve the foam plug and then pour the sand out of the pipe.
