You actually can mix copper and tin dust by hand to get bronze dust and smelt that in a regular furnace. It wastes some of the copper and tin, but it works. You can grind the copper and tin into dust with a mortar and pestle ( smooth stone and flint ). It is also handy for making more flint by grinding up gravel, and a stone hammer can turn cobble into gravel.
What I did was since there were plenty of small lead and copper ore deposits, I smelted the lead/copper into nuggets in a conventional oven, formed ingots, then used stone hammers to very inefficiently shape the ingots into plates. From there, I made my first file, which made my first chisel, which I then used to make a my first hardened clay crucible, plate mold, and burning box. Everything gelled from there.