This kind of response comes up every single time somebody asks about cast iron repair.
If it were a trailer tongue, everybody would just say "throw some 6011 on it and forget about it."
But cast iron? Everyone has their favorite tried-and-true, old-family-recipe technique... and what's worse, is you'll find many of them will actually get defensive, if not outright angry if you don't pick
their pet technique.
Brazing is indeed a common, and relatively easy fix, and generally gives good results. In your case, however, the casting is large enough that you'd need a monstrous amount of preheat, plus a large and powerful torch, and would need to take extensive steps to properly cool-down the casting afterward.
TIG brazing would need less heat from the torch, but a similar preheat and cooldown process.
Lock-'n-Stitch generally works, but is surprisingly expensive, and very time-consuming. Irontite screws, a similar process, as noted only works if you have a closed-end crack.
Bolted plates are probably a very good option in your case. If the backside of the casting is flat (no ribs, etc.) then you could drill one hole in the casting, one appropriately placed tapped hole in the plate, and bolt it on. With it thus secured into place, add three to five additional holes and bolts, evenly spaced on either side of the crack.
Use countersunk/flathead bolts, seat them slightly below flush, tighten with a dab of Loctite, and then skim it all over with a smear of Bondo. Sand and paint to taste.
Personally, on the last three machines I've had with cracks or breaks, I used an arc-welding rod known as Muggyweld. I was able to weld a previously-repaired crack in the foot of my Springfield lathe using the rod, with no preheat and no peening:
I made relatively short welds, and let the area almost completely cool between stitches. The only peening I did was to chip the slag. The only tricky part is on certain kinds of cast, I've found, you'll get porosity, which I suspect is from... maybe excess carbon or slag in the parent metal, maybe? When I got those, I ground them out and buttered in more Muggy.
The rod isn't cheap- in small quantities, nearly $10 a rod with shipping. But that weld shown only took about 3-1/2 rods or so, even with rewelds over ground-out porosity, so $35 for that fix was, in reality, dirt cheap.
Doc.
