Ben T. as others have said the pipe benders sold by Northern, Harbor Freight, etc are for PIPE not TUBE. Roll bars are made from tubing. Pipe is measured by inside diameter (ID) and schedule (wall thickness). Tube is measured by OD. Trying to use the pipe bender would be a waste of time and $$ tubing.
If you only want to do one roll bar/ cage and dont want to spend $500+ for a bender, plus the learning curve involved you have a few options.
A. Get a pre-bent bar/ cage. S&W, Chassis Engineering (sold through jegs/ summit) and a whole list of other chassis shops sell them (they go on sale periodically.) Cheapest/ easiest way to go. Downside may be shipping costs.
B. If you have an uncommon car or like to design and DIY there are a few options here:
Find a local chassis or fab shop to bend the tube for you. Around here the going price is $7.50 per bend. Roll cage might have 10 - 15 bends. Roll bar 4-10 bends. To make things easier to visualize (especially if you have bends in two planes), make a template using electrical conduit (1" or so.) Buy or rent a cheap conduit bender and bend the conduit pattern by hand. Bring the shop the template you made and they'll make an exact duplicate out of roll bar tubing.
Also some chassis companies like S&W do custom bars/ cages based on your measurements. Again shiping may be expensive if you're not local.
Bottom line is the investment in a tube bender may not "pay back" for itself after making only a bar/ cage or two.
Last edited by novajohnb; 02-06-2007 at 10:56 AM.