I have done this a lot- but I have used storebought tools that I
actually paid cash money for.
I use two different tools to do this type of thing-
A hossfeld bender- hossfeld makes flat bar edge bending dies for their
angle iron flange in die setup, and it works quite well for exactly
this sort of job. It actually uses a wedge configuration that tightens
down on the metal the harder you pull, so you can bend flat bar the
hard way in radiuses from about 6" to 36" or larger. Of course, a
hossfeld tooled up this way will run about $1500, and in this age of
harbor freight, few people want to spend that. But a hossfeld will do
this quite easily, repeatably, and to fixed radiuses. Along with doing
about 5 million other things.

The other tool I use to do this is my CP-40 Curvatricci from Eagle-
http://www.eaglebendingmachines.com/
a powered section roll designed to do just this sort of thing.
They use a series of multipart dies that bolt onto a shaft, rather
than one piece tooling with a slot milled in it. That way, you can
stack spacers up to fit any size of flat bar.
I have spacers ranging from 16ga up to about 3/4" thick, in many
different sizes, so I can always get a nice snug fit on most any
thickness bar. I like to have the flat bar just slide thru the die- a
few thousandths clearance. But if it sticks, I can always add a
spacer. The outer dies, shaped like big donuts, are about 6" in
diameter and 1" thick, while the spacers are about 2 1/2" od. This
means a 1" flat bar is completely supported in all three dies. The
radius you can bend would depend on the up and down travel of your
central roller, and the center spacing of your two lower rolls. A
machine designed to get very tight radius on small bar might be less
useful when you are rolling 2" pipe, so design parameter vary
depending on machine size- if you look on their website, you will see
the spacing, and hence the tightness of radius possible, is much
closer on the little tiny machines than it is on the ones made to roll
6" pipe.
It takes a fair amount of power to roll large flat bar this way- I do
a lot of stainless, in 3/8" and 1/2" thicknesses. But you could
probably do this small aluminum with a hand crank machine. Multiple
passes will probably be required, to sneak up on your radius, as
trying to bend the aluminum all in one pass would undoubtedly crack
it. This would make it a little tougher to get matching circles, but
certainly not impossible- you just check em against a template, and
roll again, until you get there. My curvatricci has a digital readout,
so theoretically you can return to the same setting with every new
piece of material, and this works pretty well, although even within
the same mill run, there are variations in how a piece of metal will
bend.

Now with a hossfeld, you just put on the 9" radius die, and you pull
an 18" circle every time.