Chromo being stronger is harder to bend. A prefered tool seems to be the Ridgid (believe it or not) Plumber's bender. The best one you probably need to look for on ebay. The various aircraft suppliers also sell good ones. I use a heavier one that allows me to bend up to half inch and the thicker wall thicknesses. The one I use is made by princess auto, and is a general metal strap and bar bender. I make tube dies for it on my lathe. You can see how simple the bender needs to be from Gordon's site where there are pictures on the shop tour, last time I looked. His is a production set-up as the bender is integrated into the jig. That would speed up indentical builds but is not desireable for custom work, let alone necesarry. While I take pride when I come around the fourth side and the return nails the starting point, if you are a fraction out you can somewhat tweak yourself back on line. It never seems to be tragic.