Its always the question of how far do you want to go (or have to!).... many years ago I was trying to straighten some tube and kept trying different things until I came up with the following. All wheels are driven (using the hand from my mills table) with chains. I find being able to go back and forth is really effective - keep running the tubing through and rotate it slightly for each pass. Also, you can vary the downward pressure which is important to getting it pretty close to perfect.
Robert's may be the better solution given expediency, but it was a fun little project that worked well.
