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It's not just how slow, either... it's BOTH. To drill big holes you want something that runs slow and has a lot of power. You can actually get away with about 200rpm for a 1 1/4" hole in steel, but the other end of the scale is just as important. A good rule of thumb is 500rpm for .500" diam in steel. So 250rpm for 1" and 1000rpm for 1/4", 2000rpm for 1/8" and 4000rpm for 1/16". That will give about 70ft/min, which is about right for most uses. As you can see, little stuff needs to haul butt. Running too slow is going to cause you to break little drills as they will hog in and wring off. So a press that runs 125-4500rpm can drill holes from 2" to under 1/16" in steel at the proper speeds. Now how about aluminum? Quadruple those speeds to give about 280ft/min. Yup, 16,000rpm is perfect for 1/16" in aluminum! You need to be turning about 1000rpm at poke a 1" hole in aluminum, a 1hp drill press just isn't going to pull the cut. That's why I have a 6000lb 3hp radial arm drill that will go down to 49rpm and tops out at 1100.. PLUS a bench type cheapo chinese import that runs from 350-4250rpm. I'd love to have a 20,000rpm sensitive precision press for tiny stuff, but haven't found one cheap just yet.
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