I did it by eye. I made it from the outer ring of a bearing (which is why my blade is 5 mm thick). I cut it in half, heated up one half, and forged it into a straight flat bar. Then I cut out the shape using an angle grinder (the teeth on the spine of the blade and fitted the shape for the handle) and sharpened the blade on a bench grinder. I made the holes in the blade using a drill press.