If you have ever wandered around your local hardware/woodworking store, you have probably noticed a wide array of forstner bits available. One thing I’ve noticed through the years is that some of the bits tend to clog with wood chips more than others do, especially in the larger sizes. This is annoying because you have to stop the drill and clean out the bit.
When I started comparing the bits, I discovered that the “mouth” of the bits weren’t all the same. On the bits that clogged, the sides of the mouth were nearly parallel. On the other bits, the mouth tapered out toward the top to eject the chips cleanly.
In order to create more room for the chips, I modified bits that clogged by “opening” up the mouth. To do this, file or grind back the top edges of the opening, see drawings.
There’s one thing to watch out for. Just be sure you don’t file or grind any of the cutting edges of the bit.