Countersinking is in most instances a very simple and fast operation. Surprisingly there are 147 different designs of countersinking tools in regular use. They come in at least three different materials, up to six different angles, shapes other than straight chamfers and hundreds of sizes. Today over 2700 chamfering and countersinking tool choices exist, not counting variations in tool size. Repeating that, the 2700 variations cited are just for tool design, not size. Including size variations the potential choices could be 30,000 choices. They come with integral shanks, inserted cutter, piloted, non-piloted, screw on, or slipover drill. They come as coated or non-coated tools, and with various flute shapes and even left and right hand cut. One supplier alone provides over 1500 different sizes, designs, and materials. These tools cut chamfer clearances on edges, remove burrs, prevent burrs from forming, provide aesthetic edges, and provide clearance for screw heads and rivet heads. They come in a variety of ruggedness ranging from tools that will only remove millionths of an inch at a pass to rugged ship plate countersinks. As technology moves to nanoscale products the traditional tool used will move to vacuum plating and removal process, but that is another story.

Despite these tool's widespread use, few machining references provide any details on countersinking or chamfering. Because of the criticality of those holes to aircraft life, aircraft manufacturers such as Boeing and others provide written work instructions and courses for the operators who perform the work, but few other...