Why recess a screw head
A screw driven straight into a surface leaves its head sticking up. That can snag clothing, catch a sander, or just look untidy. Recessing the head fixes this, and it also helps prevent splitting, because the screw head is not forced to compress wood fibers on its way down.
There are two common ways to recess a head, and they suit different situations.
Countersinking
A countersink is a cone-shaped recess that matches the tapered underside of a flat-head screw. The screw ends up flush with the surface or just slightly below it, and the head is visible.
This is the usual choice for general construction, cabinet backs, drawer parts, decking and anything painted. Filler or putty can hide the heads if needed.
Counterboring
A counterbore is a flat-bottomed cylindrical hole, wider than the screw head, drilled partway into the surface. The screw sits at the bottom of this hole. It is typically used with pan-head, round-head or washer-head screws, or with flat-head screws when you want a hole that can take a plug.
A plug of wood, usually cut from matching material, is then glued into the hole and trimmed flush. In fine furniture this makes the fasteners nearly invisible. Counterbores are also useful when the screw must go deep into thick stock, because they let a shorter screw bite into the second piece where a long one would otherwise be needed.
Tools for the job
- Countersink bit. A cone-shaped cutter, used after or before drilling the pilot hole. Some have adjustable depth stops.
- Combination bit. One bit drills the pilot hole and countersink in one pass. Many are made for specific screw sizes. They save time and keep the parts aligned, but you need a match to your screw size.
- Counterbore bit. A bit with a larger cutting section that cuts the wide recess and the screw hole together.
- Forstner or brad-point bit. A flat-bottom bit is a flexible way to make a counterbore of any diameter when you do not have a dedicated tool. Different bits are covered in the article on drill bit types.
- Depth stop or collar. A stop collar clipped onto the bit helps you drill repeated holes to the same depth.
Any of these tools works in a drill or driver, and a drill press gives the cleanest and most consistent depth. For lots of holes, a drill press and a stop makes the work faster and more accurate. If you are choosing a driver, the difference between a drill and a driver may matter, because driving needs controlled torque.
Basic steps for a countersunk screw
- Mark the hole location. A small punch or awl mark stops the bit from wandering.
- Drill the pilot hole. Size it to the screw. The pilot hole article describes how, including the clearance hole in the top piece.
- Cut the countersink. Lower the countersink slowly and check the fit with the screw. Stop when the head will sit flush with the surface or a hair below it.
- Test on scrap. Drilling into scrap of the same material first saves ruined workpieces.
- Drive the screw. Use a driver bit that fits the recess and keep the tool straight.
Use the clutch on a drill rather than hammering the screw until it overshoots. The clutch is covered in the article on clutch settings.
Basic steps for a plugged counterbore
- Choose the counterbore diameter. A common approach is to match a plug size you can make or buy, such as a standard-diameter wood plug.
- Drill the counterbore to a controlled depth. The recess should be deep enough to leave room for a plug thick enough to be glued firmly, which is often about a quarter to a half of an inch for typical furniture stock, but this varies with the material and the design.
- Drill the screw hole through the middle of the recess.
- Drive the screw so the head seats firmly on the bottom of the counterbore.
- Glue the plug in so the grain direction matches the surrounding wood. Aligning the grain makes the plug far less visible, so wood grain matters here.
- Let the glue dry, then trim or sand the plug flush. Take care not to sand through the surrounding veneer if you are working with plywood.
Common problems
- Head still sits proud. The countersink is too shallow. Cut a little deeper, or choose a screw with a head that matches the cone angle.
- Head sinks too deep. Soft woods compress easily. Stop a little earlier, or use the drill clutch.
- Chatter or a rough cone. Slow the speed. Metal-cutting countersinks used on wood often chatter, so use the right bit for the material.
- Splitting near edges. Move the screw away from the end of the board and drill the pilot hole carefully.
- Plug stands out in color. Cut plugs from the same board, or the same species, and align the grain.
Safety
Clamp the workpiece rather than holding it by hand, since a bit that catches can spin the wood. Wear eye protection to guard against chips, and remove the battery or unplug the tool before changing bits. This guidance is general. Follow the manufacturer’s instructions for the tools you own.