Drilling a precise hole in metal is difficult because the rotating tip of a drill bit wants to walk across the surface. A center punch solves this by creating a physical guide. You place the hardened point exactly where you want to drill, then strike the flat end with a ball peen hammer. This leaves a small pocket or dimple in the steel. The drill bit tip sits in this dimple, keeping the drill centered. Automatic spring-loaded center punches are also common, allowing you to create the mark by simply pressing down on the tool.
Mechanic Glossary
Center Punch
A hand tool with a sharp, hardened steel point used to mark the center of a hole before drilling, creating a starter dimple that prevents the drill bit from wandering.
Frequently Asked Questions
The starter dimple might be too shallow. Strike the punch again to make a deeper mark, or start with a very small pilot drill bit first.
Standard center punches are designed for mild steel, brass, and aluminum. Hardened steel will dull or chip the punch point. You need a carbide-tipped punch for hardened materials.
Grind the tip on a bench grinder, rotating it constantly to keep the point centered. Keep the angle of the point at about 60 to 90 degrees, and cool it in water to maintain the steel's temper.