Efficiencies that used to be limited to factories are now commonplace in garage workshops. Machine tools such as welders, metal saws and even plasma cutters have become relatively affordable. With your ability to fabricate metal, you'll need to be able to efficiently bend metal. You can build bending tools yourself, either for one specialized job or for repetitive production.
Simple, Two-Pronged Jig
The simplest bending jig uses two metal prongs mounted an inch or two apart. Rod stock can be placed between the prongs, then rotated around either. One prong catches the rod, leaving the other prong as an axis for the rod to bend around. These jigs can be as simple as drilling two holes through bar stock slightly larger than the machine bolts. The bolts will act as the pegs. Use bolts with a shaft that is partially threaded and partially smooth so you can bend around the smooth portion of the shaft. Screw a nut to each of the bolts until it reaches the end of the thread. Slide the bolts through the holes. Let the nuts stop them. Then fasten the bolts in place by fastening a second nut to each bolt, so the bar stock is sandwiched between the nuts. Your bolts will be fixed tight as far apart or as close together as you you've made your holes.
Using pegs can give you a crisp, right-angle bend. If you want to bend a radius into your rod, you'll need to first bend a template. You can cut the radius into hardwood such as oak, bend 8-inch flat stock around the radius, then tack-weld the radius to your jig. Now, drill holes and use the bolt technique to isolate your rod and initiate the bend around your radius. You can also weld the pegs in place.
Peg-Board and Shape Board Jig
If you want to bend a more complex shape, like a D-ring or a much more complicated shape for ornamental iron, for example, use each of these ideas in conjunction. First, design the shape you want to bend. You'll want to fasten two pegs at each point where a radius begins. Fabricate larger or compound radiuses. Then, use the drilling method for your pegs. This makes the pegs removable, which may be necessary for compound bends. For example, you may have to bend your rod clockwise around one radius or shape, then insert one or more pegs before bending counterclockwise to come out with the desired shape.
Levers and Bottle-Jack Power
Each of these concepts can be done with hand-power to bend the rod, if the rod is small enough. A tube may be slipped over the rod to give you more leverage. If you're trying to bend a rod without the help of a long extension handle, and it's too tough, consider fabricating a lever that will exert force directly adjacent to your bending axis. If an extension or mechanical lever still isn't enough, fabricate a mechanical lever out of flat stock, which will accommodate a small bottle jack. The hydraulic strength of inexpensive bottle jacks will give you the mechanical force to get your job done.