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Rectangular holes: One of those square punches will work on sheet metal, but not on thicker plates. I've only made a couple square holes in aluminum, so YMMV. I drilled a smaller hole in each corner, then used a larger bit to remove the majority of the diameter. Then a file finished it up pretty well. Depending on thickness, I could see a Dremel with appropriate tool doing a pretty good job filing if you only have one or two holes to make, and have a firm, steady hand.
Drill speeds: The current Fastenal catalog has a drill speed chart mixed in with the drill bits section. I'll bet that the cast few catalogs have had the charts, also. Unfortunately, it only lists the SFM, and not material being drilled, and drill bit material. I usually just use about 75% the speed on the chart on my drill, as this seems to work the best for my tools and materials.
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