Ah! aceshigh. What you have there is a pipe bender. The outside diameter of pipe is different to tube, so the tube won't be properly supported for bending. Also pipe usually has a heavier wall than tube and is less likely to kink anyhow. Tube benders usually have more sophisticated arrangements. Try going to a hardware store and looking at the tube benders they sell to plumbers for 1/2" copper tube and you will see what I mean. Imagine this sized up to 2" tube with hydraulic rams and you are looking at thousands of dollars. Try hydrodude's tip of filling it with sand, plugging the ends tight, heating red hot and forming it around a 4" pipe. This will work with practice, but is hardly a commercial proposition.