Metal cutting involves removing excess material from a workpiece using various tools to create a finished part that meets specifications. There are manual metal cutting methods like saws, chisels, and shears as well as machine methods like turning, milling, drilling, and grinding. When manual cutting is impractical, machine cutting tools like lathes and bar cutting machines are used. Lathes remove metal from a workpiece to shape it according to the operation being performed, while bar cutting machines can cut multiple rods simultaneously using hydraulics.