On my aluminum Hammond chassis I used hole saws since I already had them. I'm pretty sure they are the cheapest thing to buy. I originally got them to build guitar amps where the chassis is hidden. On my Cornet and Clarinet they worked fine, although they needed a bit of touch-up with a rounded file to square up the edges of the holes. I also painted my chassis with the hammered type paint, and that covers up scratches and other flaws. I haven't tried a step bit and I've always heard the Greenlee punches are great but $$$. Good tools are always nice to have, though. Good luck...