I've broken part of the bottom lug on the caliper where it mount to the hub if I vee prep and weld it or bronze it (still have the broken bit) will it fail or is caliper a bin job

Broken brake caliper, you say? Don't know about you, but no way would I trust a repair regardless how well it was done.

_________________
Simon

The adventures of an owner builder in the Tallarook Ranges

Bronze weld with oxy is stronger than the parent metal (it's only grey cast iron). You will need to preheat it slowly and retard the cooling rate when finished, with a fire blanket or similar.
You are not supposed to weld brake parts though.. (but, who would know).
However, new or s/h calipers are not ridiculously expensive. I would just replace it.

_________________
DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

I don't like to throw anything away that is salvagable and something that can be welded or brazed etc can be repaired, HOWEVER we are talking about a fairly critical brake component so - although it will hurt - throw it and get another.