A single copper mine can burn through tens of thousands of tonnes of steel balls a year, and almost none of the good ones are cast. They are forged, because how you make a 5-inch sphere decides how long it survives inside a grinding mill. Forging steel balls at industrial scale usually means skew rolling, one of the more satisfying processes in all of metalworking to watch: • A round bar is heated to roughly 1000-1100C, glowing orange and soft enough to flow • It feeds axially into two rolls spinning the same direction, each cut with a matching helical groove • The groove simultaneously rotates the bar and pinches it, squeezing out spherical segments in a continuous spiral • At the end of the groove each finished ball shears free, no flash, no trimming, almost zero scrap The output is a near-net-shape ball every couple of seconds, with grain flow wrapped around the surface instead of cut through it. That continuous grain structure is exactly why forged media resists cracking whe...