Benjamin Forstner invented this clever drill bit back in the mid-1800s. It has a cutting rim or teeth around the perimiter and a small spur in the center.
The bits come in a variety of sizes, up to two inches or more in diameter.
The idea behind this bit is to bore exceptionally clean holes that leave a virtually flat bottom.
One of the limiting factors of Forstner drill bits is that they tend to skate or slip. They are therefore best used in a drill press.
On the other hand, the Forstner bit is ideal for overlap boring because the outside cutting rim keeps it from slipping into an adjacent hole.
In fact, the bit is so stable in a drill press, it can be used to bore straight and true even when drilling a partially exposed hole.
So it looks like we owe Mr. Forstner a debt of gratitude. This is one bit that's been around for 150 years and will probably be around for quite a few more.
