Step drills are great tools for drilling clean holes in thin aluminum. They excel for holes that fall between the smaller holes required for most hardware, which are best step-drilled to size with sharp, standard drill bits, and larger holes, such as inspection holes, which are best accomplished with a fly cutter, holesaw, or a hole punch and die.
A downside to step drills is the narrow steps between the integrated hole sizes. It is all too easy to overshoot or undershoot the desired hole size. That problem is solved by marking the desired hole size. Doing so frees your mind to concentrate on getting a good hole, rather than worrying about oversizing the hole. It allows you to apply the pressure needed to cleanly and quickly bring a hole near its final size and provides a visual cue when it is time to ease back on the pressure, to avoid oversizing the hole. Of course, a sharp step drill that has not been abused is also key to good results.
I imagine Kerry intended this when he said “paint”, but a colored felt marker works well.
David…just saw your post after my Sharpie post…
I’ve always used a strip of masking tape, but I like your idea much better. Perhaps a red Sharpie instead of paint? I’ll have to see if the Sharpie will be as visible… Comes off with acetone. Thanks, Kerry.