I do this all the time on my hossfeld bender.
You can use the fixed radius dies for angle iron, and bend flat bar the
hard way.

I also use my real 3 roll bender- and it will do this quite easily too-
but mine is powered, and cost real money.
http://www.eaglebendingmachines.com/

1/2" x 1" is thick enough that it works pretty well, although its
harder to hammer back flat if it does get crooked.

Most handcranked rolls dont have the oomph to bend flat bar the hard
way, even aluminum. My power rolls are 3 hp....