I can tell you from experience that with .065" thinwall material you won't get a bend less than 10" or 12" centerline radius without busting the pipe...When you fill it with sand, the outside wall of the pipe stretches around the bend. The wall thickness is not thick enough to stretch that far, and heating thinwall evenly to bend it is hard to do..it just doesn't stay hot long enough to get the bend done..
You could try to do it in small increments, and maybe if you have a bunch of patience, you can get a smooth 90*. It still won't be a tight bend.
Use thick material, at least .125" wall, and fill it with sand or steel shot. You still won't get any better than 5 or 6 X the diameter if you use a bender of some type.
Or do as others have said...buy the pre-made mandrel bends. A mandrel bent tube can have a centerline bend radius as small as 3X the diameter of the tube. If you look around you can find them in SS too. I'd buy the U bends, they have a long leg and can save you a weld.
Conduit bender won't do pipe or tube correctly,, unless you have the right dies...the conduit is sized differently than pipe or tube and the wrong dies will kink thinwall . ( Besides a Hossfield #1 bender , I have 2 Greenlee conduit benders in my shop. An old hydraulic incremental as well as a nice one shot bender. I know what they will do.)
my signature lines...not really directed at anyone in particular..
BE different....ACT normal.
No one is completely useless..They can always be used as a bad example