The makeshift forge is where we find either Malcolm Stein, the dwarven blacksmith, or an Order Armorer if Geralt chooses one side or the other in the fight. Whichever one is there will be the one to make Raven's armor for the witcher. If Geralt choses the Witcher / neutral path, then he uses the services of Kalkstein to fashion Raven's armor and this forge is not used at all.