In-Game Bug Report by Tarlin: Coal, steel and other items that require a furnace can be produced in a workbench. I am reporting this as a bug becuase it seems illogical that the furnace is necesarry to manufacture these items, also the furnace requires a fuel source, but these items can be made inside the workbench without consuming any fuel to produce.
#IGBR: Workbench production items
hollow finchBOT
gaunt turret
It's deliberate. The workbench is the fallback for almost everything. But also very inefficient for ingots as they are used in almost every recipe and it needs a person to operate. A furnace needs fuel, but not a person - when completly automated.