Step drill bits are used to drill metal up to 1/4 of an inch thick. Step drill bits are designed to enlarge a hole as the bit drills through the sheet metal. Each step on the bit is larger in diameter than the step before. Smaller step drill bits are self-starting and no pilot bit is required to start the hole. On larger step drill bits, you need to have a hole pre-drilled that is equal in diameter to the smallest step on the bit.
Put on appropriate eye protection (safety glasses or goggles).
Place the tip of the center punch on the metal to be drilled at the location of the desired hole. Hit the blunt end of the center punch with the hammer to leave an indentation (referred to as a center mark). This indentation will provide a place for the drill bit to "catch" so it doesn't drift to the wrong location on the work.
Secure the self-starting step drill bit into the chuck of the drill motor. Apply cutting and tapping fluid to the center mark and the step drill drill bit.
Align the tip of the self-starting step drill bit with the center mark on the metal's surface. Depress the drill's trigger to start drilling the hole. Run the small step drill bit completely through the metal. Apply additional cutting and tapping fluid as necessary to keep the step drill bit cool.
Release the chuck of the drill motor to remove the small step drill bit. Secure the large step drill bit into the chuck of the drill motor. Insert the small tip of the large step drill bit into the hole you created in the metal. Apply cutting and tapping fluid onto the large step drill bit and around the hole in the metal.
Depress the trigger of the drill motor to run the large-diameter step drill bit into the hole. Stop drilling frequently to apply additional cutting and tapping fluid to the drill bit. Stop drilling when the hole has reached the desired diameter.
Remove the large step drill bit from the drill motor. Clean both step drill bits with a rag to remove metal shavings from the bits. Clean the metal shavings from around the hole that you drilled in the metal. Store the drill bits in a tool box or drill bit container to avoid dropping them or otherwise damaging them.