A field tillage tool, a disk, is composed of dished steel plates, a bit bigger than frisbees. Originally sharp, soil sand and rocks take their toll on the edge. Every few years the disk was disassembled, and the discs taken to the blacksmith for sharpening. They were spun slowly as the grinding wheel was advanced to the edge. Sharp discs made for easier pulling. In the 60s, some men had traveling setups that could sharpen each disc without disassembling the entire machine. Minimum tillage planters have pretty much eliminated the disk. On rough or hard ground, we would disk first, to knock down weeds and grass, plow, then disk again to break up the clods. In some parts of the country the discs were nearly 24 inches diameter and serrated. Am an old farmer, just ask.
