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Pete, what does the term "hot short" mean? Have not heard that before.
For bar stock, heating to a dull red then cooling to anneal it helps bending, but I have no experience with cast brass so don't know if that behaves differently, how hardened if any it is after casting. Alloy 360 does bend a decent amount when annealed. You may need to have the form set to overbend slightly to allow a bit of springback.
A 10" diameter x 1/4" thick flat cast red brass/bronze disc being bent to the form of a 15" radius is a big ask The original from 1895 would I suspect have been as cast from a pattern of the required diameter.....such material castings from this period are prior to any form of vacuum degassing so would be of extremely course granular structure & somewhat brittleThe material would also exhibit a very low tensile strength and yield point, both of which are not conducive to any bending action Lettering/numerals cast in the flat plane would grossly distort and tear when bent to the 15" radius ......Heating brass to annealing temperature is to relax a work hardened molecular layered structure.... and not intended or sufficient to alter the course granular as cast structure You could consider replicating the original by producing a 15" radiused pattern & sand cast the requirements ......just like the original Derek
Does it have to be cast? Could it be CNC cut from one of teh bending brasses like CZ108 and then simply pressed over a wooden former with suitable cope. Or even bend first and CNC with a 4th axis to cut the face leaving the letters proud as if cast.