Back in his day, before acronym government, my pop build furnaces for school system metal shops.
Said it was nothing, made a mold, poured concrete, hooked up a blower to the gas jet.
Heat up to melt aircraft aluminum. I think that is enough for softer metals such as copper and pm's.
Sand casting is fun.
Your father reminds me of a handy guy my father knows, he only finished grade school and then kicked around shops and picked up skills and ideas, joined the Navy back in the 50's and was a fabricator...he could do all the engineering math and design from scratch and make anything. His house in the woods has many interesting gadgets and it appears there is nothing he can't figure out or do. A guy like that in a TEOTWAWKI world will be worth his weight in gold, if not more!