Q: I am now the proud owner of a plunge router. How do I choose the right bits for it? I’ve checked several displays at the home centers, and there are no clear divisions between “fixed” and “plunge” bits.
A: Identify a plunge-cutting bit by looking for a cutting edge that crosses the tip. The carbide-cutting tips of the bit on the left jut above the steel body, which is flat on top. Plunge it and only the tips cut: when the steel hits the wood, it stalls the cut. It’s not a plunge-cutting bit.
The bit on the right has an extra carbide-cutting tip crossing its tip. The maker identifies it as a plunge-cutting straight bit, and the extra carbide makes it more expensive than a more conventional straight bit of the same diameter.
The commonplace design for straight bits is seen in the middle. The steel body between the carbide tips is ground to form a ridge. It may not be particularly sharp, and it may not seem to be a cutting edge in the conventional sense, but the shape is sharp enough to enable the bit to plunge.
You can buy bearing-free profile bits that cut grooves, and these bits will plunge. A core-box bit is a coving bit without a pilot. A V-groover is a chamfering bit without a pilot. Shop around and you'll find pilot-free, plunge-cutting bits that form roundover and ogee profiles.
All of these bits have cutting edges extending across the bit’s tip.