Brazing is what I call a "forgiving process" for cast iron repair. Brazing metal is somewhat ductile, and can absorb stresses set up when a brazed part is cooled. Brazing metal also can be "walked" or gotten to flow by playing the torch flame to create proper fillets and to enter tight areas on a joint.
The big question with the repair to the bandsaw table "crescent" casting is whether appearances are important. I may have missed something the OP wrote, but if appearances are not important while functioning of the part/bandsaw is, then brazed repairs can be left "as brazed".
My own approach to repair brazing of cast iron parts is similar to what the OP describes. I try to leave a bit of the fractured areas intact and this serves to accurately align the broken pieces. Where possible, I try to add some steel reinforcement across the breaks, sometimes fastening the steel "fish plates" or "repair plates" with socket head screws and reamed-and-fitted dowels. This puts the load transfer thru a mechanical connection rather than the brazed joint.
I've had good luck repairing cast iron using uncoated "low fuming bronze" rod and a powdered blue flux made specifically for brazing cast iron. I've also had good luck using the old "Oxweld Brazo" flux in the yellow-and-black can. The pre-fluxed bronze brazing rods work OK, but the flux deposit has made for some problems with "wetting" of the iron to be brazed.
Cast iron welding is an art unto itself as John Ruth has pointed out. The square cast iron rods for oxyacetylene welding of cast iron are hard to find these days. I remember reading articles as to how large broken iron castings were repaired by O/A welding, and was amazed at the heavy castings that were successfully repaired. In old O/A welding texts, the method of repair welding iron castings called for a high preheat in a charcoal fire or similar, and keeping the preheated cast iron parts covered with insulation except for the weld areas. A high post heat with some "soak time" and very slow cooling finished the job. I know some oldtimers broke old automobile piston rings and usedf them as filler rods for cast iron welding on small work.
The other issue is the composition of cast irons. Old cast iron from many years ago was melted in cupola furnaces. These were fired with coke, and the charge of iron melted and ran down thru the coke and out the spout of the furnace when it was tapped. The furnaces were charged with broken pieces of scrap cast iron- stuff like old engine blocks, old steam heat radiators, and similar being common. In some foundries, a percentage of new pig iron of known composition was added to each melt. In those days, cast iron was truly cast iron. It was a "gray cast iron". Machine tool builders often specified a certain percentage of scrap steel to be added to each melt, and had tighter specs on things like carbon and manganese.
In more recent times, post 1976 (the Clean Air Act taking effect about that time), cupola furnaces were outlawed in the USA. Surviving iron foundries went to using electric furnaces to melt their iron. These are either arc or induction type furnaces, and require a significant amount of steel in each melt for these types of furnaces to work properly. The result is "real cast iron" is not often found in castings poured in the past 40 years. The amount of scrap steel in each heat makes these types of cast irons more of a "semi steel", and a whole lot easier to braze or weld. Some people claim to be successful in welding "cast iron" with carbon steel electrodes or MIG wire, and I've had my doubts as to the soundness of those welds. Usually, when real cast irons were welded with steel filler metals, carbides would be precipitated out at the weld zone, forming a very brittle and highly stressed area. Usually, on cooling, these welds cracked. With enough steel in the new types of cast irons, chances are there is just enough steel to prevent or reduce the formation of carbides in the weld zone.
Old cast iron, the stuff made "way back when" in a cupola furnace is not going to "take weld" too easily. Using a cast iron filler rod so the weld is nearly homogeneous with the base metal is one way to get a good sound weld- with proper preheat and post weld heating and cooling. Using a repair electrode such as a "Ni Rod" introduces a nickel alloy into the weld zone. Some Ni Rods are machineable (and a good bit pricier), while other less expensive Ni Rods, used for things like stove grate repairs, produce welds which are not machineable.
My 'druthers, being old school, is to stick with brazing for this repair. Since the base metal should not be melted, if the parts do not "take braze", clean them up and try again. Another word of wisdom from old-timers: when preparing cast iron for brazing, they avoided using grinding wheels. The belief was the grinding would smear the free graphite in the cast iron onto the surfaces to be brazed, preventing "wetting" from occurring. The old timers told me they would file, chip, or use a burring tool to prepare a cast iron joint for brazing. I do this as well, though I've had no problems using an angle grinder to vee out and follow the line of a fracture to prepare it for brazing.
Cast iron is one of those metals which does not become plastic when raised above its transformation temperature- as steel does. Cast iron will get to a dull red, and then with not much more heat, it will puddle. This makes it a bit trickier to manage then when welding steel.
Oxyacetylene welding of steel is how I learned to weld as a kid. Coathanger wire for filler and some scrap thin steel. I learned to manage the puddle. I've never tired O/A welding of cast iron, but from using Ni Rod for stick welding, it seems a bit trickier all around.
Before I risked trying cast iron welding on a part like the saw table sector, I'd get some OLD scrap cast iron (stuff over 50 years old), and try my hand at O/A welding it together. Trying O/A welding on the newer cast iron might give a person a false sense of security, given the percentage of steel in the newer cast irons.
