Primary processing refers to the processing of raw materials. For example, if you want to make a cube of 100X 100, you need to finish the surface with a grinder. Then you need to buy raw materials of 105X 105X30000 for processing and cut them into cubes of105x105, which is the initial processing. Then put it in a milling machine or machining center and mill it into a square of100.2x100.2x100.2, which is rough machining. Then it is processed on the grinder to100x100x100, which is finishing.