How to Countersink a Hole in Metalby C.L. Rease
A countersink screw has a taper that is largest at the head and reduces in size until it reaches the threaded shaft of the screw. Creating a countersink in the metal allows the head of the screw to rest below the surface of the metal and provides the full structural strength of the screw. The countersink drill bit used to create the chamfer in the metal must match the size of the screw head you will lose the structural integrity of the connection.
Wearing your safety glasses, place the arbor of the countersink bit into the chuck of the drill motor. Tighten the chuck to hold the counter bit securely in the drill.
Place the center of the countersink bit into the hole that you need to countersink.
Apply pressure down on the handle of the drill and begin drilling by depressing the trigger of the drill.
Stop drilling when the cutting edges of the countersink drill bit meet the surface of the metal.
Slide the screw into the countersunk hole and run your hand over the surface of the metal, across the countersunk hole, to feel whether the head of the screw protrudes above the surface of the metal. If the head of the screw does not rest below the surface of the metal, withdraw the screw from the hole and run the countersink drill bit deeper into the metal.
Insert the countersink drill bit into the other side of the drilled hole, if accessible, and run the countersink drill bit quickly into the hole to remove any burr that might remain from the drilling process. This will allow the countersunk screw to pull the metal tightly to the connecting material.