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The spade drills work well but they are not available in all sizes and they are limited as to how thick a piece of steel they can drill through relative to the diameter of the drill.
The straight flute drills, marketed under the brand name of Hi-Roc (among others), come in just about any size and will drill through any thickness of material they are long enough to reach through. As stated above, they are relatively expensive but they are worth every penny when you really need one. They are available from MSC, Enco, McMaster-Carr etc.
You will need to use them in a drill press as mentioned earlier but I have never believed the conventional wisdom on their use that says to use them at high speed with no lubrication. I have done that and it works fine but I normally use slow speed and lubrication and find that works fine as well. If I do break one (very rare) I'd rather do it at a slow speed ...
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