Drilling sheet metal looks simple until the bit grabs, walks, or punches a jagged triangular hole. With the right bit and a little technique, you can drill clean, round, burr-free holes every time.
Why Sheet Metal Is Tricky
Thin material has almost no depth for the drill point to engage, so a standard twist drill can catch and lift the workpiece just as it breaks through. The tip of an ordinary bit also tends to punch through before the full diameter is cut, leaving a hole with three lobes instead of a true circle. The fixes are the correct point geometry and control of the breakthrough.
Choose the Right Bit
- Step drills: Ideal for thin sheet; each step sizes the hole and self-deburrs as it goes.
- Split-point twist drills: The split point starts on contact and resists walking.
- Sharp, quality bits: A crisp cutting edge shears cleanly instead of tearing.
Our sheet metal drill bit guide covers these styles in detail, and American-made bits hold their edge through repeated holes.
Speed, Feed and Lubrication
Run slower than you might expect, especially in stainless steel, and keep firm, steady pressure so the bit keeps cutting rather than rubbing. Rubbing work-hardens the surface and dulls the edge. A drop of cutting oil on steel and stainless reduces heat and improves finish; aluminium cuts freely but still benefits from a little lubricant to prevent the bit clogging.
Control the Breakthrough
Clamp the sheet firmly, and back it with a scrap block of wood so the bit exits into support instead of open air. This single step eliminates most grabbing and triangular holes. Ease off pressure just as the bit begins to break through.
Deburr and Finish
Almost every drilled hole in metal leaves a small burr. Knock it down with a deburring tool, a larger bit spun by hand, or a countersink so edges are safe and parts seat flat. For heavier gauge and repeated production work, larger metalworking bits give you the rigidity you need.