Thanks for digging up this old thread. Since originally posting it I have created some additional dies and rollers. The details can be found here in my journal
beginning with entry #306 and following.
Here are a few pictures of the improved die and some resulting bends.
I sliced off a 1" wide section of 6" diameter pipe as the basis for my die to bend curves with 3" radius.
I then welded 1x2 rectangular tube on each side to hold the curve.
1/4" steel rod is then welded in the middle of the curve. This in-dents the tubing during bending and helps prevent kinking.
Here's the die in the bender.
And a couple shots of some bends. Note the in-dent made on the inside of the curve by the 1/4" steel rod and also note that the top (outside of the curve) automatically in-dents as the curve is made and the metal stretches (shown in the second photo below).
I did a ton of bending for the sedan delivery project with this die and it worked out pretty well. Be aware, when doing 90 degree bends or greater, the sides of the square tubing will also buldge out a bit and become wedged between the 1x2 tubing supports on each side. On occasion I have to bang the tubing out of the die with a hammer.