Re: square steel tubing
Bending the square tube would take about three to four times the radius you can bend round tube of the same diameter and thickness. They are much more difficult to bend without buckling. The easiest way to handle it is to slot the square tube with a hack saw with a bunch of hacksaw kerfs in a row, bend the tube and then weld up the slots. If done carefully this can work well and look good. To keep the bend looking reasonably smooth and not like a series of flats the kerf slots have to be pretty close together, around 1/8" apart. An air driven die grinder will do the job or a regular hacksaw. But an electric angle grinder would make too wide a kerf slot to look good, the slots should be in the range of 1/16" or so spaced about 1/8" apart.
Goldwing 1500, Silverwing 600, Schwinn 49