Prior hot rolling hammering was the technology used for shaping the iron into bars. Water powered hammers were first introduced in the l5th century, at Karmansbo 400 years ago.
The speed of this helve hammer was 60-80 strokes per minute. The finishing of the bar to desired dimension and surface took 1000-1500 strokes and up to 15 minutes to make one bar. Maintenance was important as the wear was huge and the hammer had to be operational around the clock. Exceptional skill was required to quickly shape the iron into bars of desired dimensions.