Drilling Large Holes in Sheet Metal: The Step Drill Bit

Have you ever tried to drill large holes in sheet metal, for example, 0.5 inches in diameter? If you did with a regular drill bit (AKA twist bit), you may have had to quit due to the intense vibration and/or the hole turning out more like a Reuleaux triangle (below) rather than a perfect circle. The difficulty is special to thin sheets; the same drill bit will work on the same material of greater thickness.



I had many troubles with this, on both 7075-T6 aluminum (aircraft grade, 0.025") and stainless steel sheets (~24 gauge). Drilling large holes with twist bits seemed practically impossible. I tried different RPMs on my drill press as well as pilot holes, but nothing seemed to work well. I began to think that my 1/3 hp drill press was too weak. Before considering buying a new drill press, I decided to try the step drill bit from Amazon for around $12 (pictured below). The bits go to diameters of 1/2" and 3/4".



These things worked like a charm. Vibration and noise were reduced to the level of drilling small holes. Progressively larger diameters are drilled out step by step. These are the clear solution to drilling large holes in sheet metal. They also can be used to deburr rough holes and can function as all-in-one drill bits for materials as thick as the steps.