The Catalan forge consists of a boiler room fire and a hammer, said hammer, whose movement is provided by a paddle wheel driven by water. A cam driven by the wheel, can lift a hammer 100 to 250 kg, which strikes an anvil on a regular basis (100 to 125 strokes / min). With this hammer artisans were able to manually shaping parts with an accuracy of one millimeter, before the metal has finished cooling down.