Other Countersink Styles
Although there’s not always a lot of call for it in many woodshops, there’s a specialized countersink for making rustic log furniture with round mortise-and-tenon joinery. Once a hole (the mortise) has been drilled to accept the round tenon of a furniture component, these wedge-shaped countersinks easily taper the top of the mortise to exactly match the tapered shape of typical round tenons. The mortise-and-tenon joint mates perfectly for a very strong connection. These countersinks are generally used with a heavy-duty drill.
Not all countersinks require a drill, however. Hand countersinks consist of a handle similar to a screwdriver’s, with individual countersink bits that snap into the front. First, drill your hole and then, with a few twists, you have a basic, no-frills countersink ready to accept the screw. They’re excellent to keep within arm’s reach or stashed in the toolbox for making a quick countersink or two without taking the time to fetch your drill and regular countersinks. These guys do take a bit of muscle power, however, and your wrist will get its exercise if you make several dozen countersinks in oak with one of these. But for a quick one-off countersink, they can’t be beat.
The most important thing to keep in mind when using a countersink is to match the size correctly to the screw being used. This goes for all aspects of both the pilot hole and the countersink itself. A too-large countersink will swallow the head of a screw in what will look like a moon-sized crater; a too-small countersink won’t fit the screw head, and forcibly driving the screw in can tear the wood fibers around the countersink. If you don’t drill the countersink deep enough, the screw will remain proud of the surface; go too deep and the screw will seat too shallow. With use, you’ll quickly get the feel of particular countersinks, but until then it’s wise to adjust all your settings (drill bit depth, countersink size, depth stop location) and make a test drill into a piece of scrap before drilling the real workpiece.
When countersinking, speed isn’t always your friend. Drilling too fast can lead to too-deep or too-large countersinks, especially in softwood. High speed is also one of the main causes of “chatter,” a countersink with a ragged edge and an inner surface that is chewed up in an undulated pattern.
For traditional tapered wood screws, a countersink with a tapered drill is logically the best to use. Straight wood screws, such as those ubiquitous black screws from the home center, work optimally with straight drill bits. However, in most uses except in the hardest of hardwoods, the type of drill bits used in countersinks are interchangeable. In softwood, the difference is negligible.
Keep a close eye on the drill bits in your combination countersinks. Like any bits, they cut inefficiently when dull. Remove them as needed and replace them. Just about all countersink manufacturers make replacement bits that are easy to swap in.
Same goes for the cutting edges of the countersink itself. Sharpen them as necessary or replace them. Again, all the manufacturers offer replacements. (In some cases, the replacement cutters are sold together with new drill bits.)
Other Countersink Uses
One of the biggest conveniences a good countersink provides is being able to drill a pilot hole and the proper countersink, and simultaneously put both at the bottom of a deeper hole that will accept a wooden plug. These deep countersinks are sometimes referred to as “counterbores,” but that’s technically not quite accurate.
You can make deep countersinks easily by setting the countersink’s depth stop to allow the countersink to drill more deeply into the worksurface. Be sure to measure the size of your plug to be sure your countersink’s body will make the right-size hole. Likewise, set your depth stop carefully. As mentioned earlier, a quick test drill in scrap is always a good idea when making adjustments to countersink sets.
Speaking of depth stops, be careful with them. There’s no need to ram that countersink down into the workpiece until the depth stop bangs to a stop. All that will get you is a marred surface. And if you don’t stop drilling soon enough, the spinning depth stop can easily burn the wood surface to boot … yet another reason to avoid high-speed countersinking. The most efficient way to make a countersink is to take it easy, and decrease the drill speed as the stop nears the surface. When it just barely kisses the wood, you’re done.
It’s likely that after you get used to how a particular countersink works, you’ll leave the depth stop in its case. Once familiar, you’ll be able to tell the correct depth instinctively.
There’s one last task at which countersinks excel, and it has nothing to do with wood: they are the fastest, most efficient way to deburr a freshly drilled hole in metal. You might not think there’s a lot of call for that in the woodshop, but think again. Drilling holes in hinges, metal angles, jig components, cast-iron for table attachments, shelf brackets and the like all leave an unsightly — and dangerously sharp — burr around the edge of the hole. One quick touch with a countersink removes this burr.
It’s best not to use your regular woodworking countersinks for this task, however. Instead, pick up a couple of cheap, one-piece fluted countersinks just for the purpose. (They make expensive countersinks for metal drilling, but for occasional deburring, the cheapest you can find will do the trick.) Keep them with the drill bits you normally use for metal, and you can’t go wrong.