Originally Posted by gugie

We'll have to agree to disagree on the brass (bronze) filler. Bronze may not be as strong as the steel, but you can use more of it to compensate. That's why a bronze fillet brazed frame is as just as strong as a lugged one.

Crack propagation is a study in fracture mechanics, a field that I haven't studied much, but what you're trying to do is remove stress risers. In many cases you actually want a softer material. I wouldn't fill this hole with brass, I'd make/machine a small plug and silver braze it in. That keeps the heat affected zone down to a minimum. Filling that large a hole with brass filler would take some skill.