This video shows the process I use to make belt buckles out of steel or stainless steel. I cut mine from 3/16" plate. You will need a welder (preferably TIG), a drill press, a belt sander, and some miscellaneous tools to make buckles with this method. If you have a tumbler, a great way to pre-finish the buckle is to tumble it with coarse media for a day, then go over the surface with non-woven abrasive pad or belt. Alternately, you could powdercoat, paint, patina, electroplate, etc.