Zero-Flute Countersinks

I’ve been using the same five countersinks for decades. While they’re all different—one has a single flute creating a cutting edge and two have a pair of flutes; one has five flutes and another has seven—the one thing they have in common is that none of them works very well. On all of them, the cutting edges of their flutes are square to the circumference, so they scrape rather than cut. And as scrapers, they’re rather crude, lacking the sharpened burr of a cabinet scraper. What’s even worse is that countersinks chatter. The irregularities in the wood’s density cause the countersink to get nudged off-center, and the resulting vibration makes for some odd-shaped recesses that are anything but round. (Countersinks that are attached to tapered bits for wood screws are prevented from chattering by the drill bit. That’s also the case with countersinks with integral pilot tips sized to fit a particular predrilled hole.)

Photographs by the author

The set I bought came in a padded case. The countersinks are precision tools with sharp cutting edges and are well worth protecting.

Small Boats reader Steele Hinton recently mentioned that there is one type of countersink that cuts cleanly and without chatter, by not having any flutes at all: the zero-flute countersink. It has a smooth conical tip with an upward-angled hole bored in one side. The sides of the hole meet the conical surface at an acute angle, about 45° (the equal of a bench plane’s blade to its sole), so it’s poised to shave rather than scrape. I could hold that edge against pine and oak and carve curls of wood, which is impossible with an ordinary countersink.