You have to know the limit to heed it

Every drill bit has its optimal speed where it cuts quickly without burning. You can keep a drill-press speed chart handy, but here's a no-fuss way to get the right speed for bit sets that come in cases. Write the recommended speed next to the bit inside the case, as shown below. Here's the method I use: On the top line, I jot down the softwood speed; below that, the hardwood speed. To save space, I drop the last two zeros from the number. For instance, 600 rpm would be expressed as a 6. A 23 indicates 2,300 rpm.
—John Anderson, Long Island, Va.