Pro Tips for Drill-Driving Screws
The task of driving screws improved exponentially about 30 years ago with the advent of the battery-powered cordless drill/driver. Today, the ubiquitous drill/driver is the go-to tool for virtually every hole-drilling and screw-driving job. However, to power-drive screws with speed and precision takes practice, patience and a few tricks-of-the-trade. Here are six tips and techniques to help you maximize the screw-driving capabilities of your cordless drill/driver.
1 Back Off the Clutch
Every drill/driver has a slip clutch, which allows you to control the drill’s torque (power). It’s the adjustable collar located directly behind the chuck. The numbers on the slip clutch represent the amount of torque, or twisting power, that the drill produces. The higher the number, the more torque delivered to the screw head.
Learning to use the slip clutch properly allows you to drive screws to precisely the correct depth without under-driving them so that their heads stick up, or over-driving them right through the board. Here’s how a slip clutch works:
As you drive in the screw, the slip clutch monitors the amount of torque applied to the screw. If the force require to drive in the screw exceeds the slip clutch setting, the clutch will disengage, or “slip.” At that point, the chuck stops turning, but the drill motor continues to run.
It takes a little practice to know where to set the slip clutch, but it’s best to start at a mid-range number. For example, if the drill has 30 clutch settings, set the clutch to 15 and then drive in a screw. If the clutch slips before the screw is fully driven, rotate the clutch setting to a higher number. If the drill drives the screw too deeply, reduce the amount of torque by adjusting the clutch to a lower number.
Generally speaking, use higher slip-clutch settings to drive in large, fat screws, and lower numbers to drive small, thin screws. However, you must also take into account the hardness of the material you’re screwing together. Driving screws into plywood and softwoods, such as pine, cedar and fir, typically requires very little torque. But, if you hit a knot or particularly gnarly section of wood grain, you’ll have to crank up the clutch. Driving screws into hardwoods, such as oak, maple and mahogany, requires more torque and higher clutch settings.
2 Bore Clearance Holes
Mastering the slip clutch might be the most important screw-driving skill, but coming in a very close second is learning to drive screws without splitting the board.
The first step is to bore a hole through the top board that’s equal to or very slightly larger than the diameter of the screw shank. This hole, known as a screw-shank clearance hole, permits the screw to pass cleanly through the top board. And that’s important because without any friction in the top board, the screw can pull the two boards tightly together.
Clearance holes are particularly important when driving screws close to the end of a board or very close to the edge; both places where splitting is common.
3 Drill Pilot Holes
A pilot hole works in conjunction with a screw-shank clearance hole. A pilot hole is a small-diameter hole that’s bored into the bottom board. Its purpose is to provide a path for the screw to enter the board without splitting it. Again, it’s important to bore pilot holes near the ends and edges of boards, but they’re also recommended when screw-driving into hardwood or any thin board.
The properly sized pilot hole will also prevent screws from snapping in half, which is especially important when driving screws made of brass, a notoriously soft metal.
4 Chart Your Course
Below is a chart to use as a general guide when drilling screw-shank clearance holes and pilot holes. Note that pilot holes in hardwood are slightly larger than those for softwoods.
Information is given for the five most common screw sizes, ranging from Number 4 to Number 12. (The larger the number, the fatter the screw.)
Screw Size Clearance Hole Pilot Hole Softwood Pilot Hole Hardwood
4 7/64 inch 3/64 inch 1/16 inch
6 9/64 inch 1/16 inch 5/64 inch
8 11/64 inch 5/64 inch 3/32 inch
10 3/16 inch 3/32 inch 7/64 inch
12 7/32 inch 7/64 inch 1/8 inch
5 Countersink vs. Counterbore
The most common screw used today to join wood is the flat-head screw. In most cases, you’ll want to drive the screw head either flush with the board’s surface, or below the surface.
To make the screw head flush, you must use a countersink bit to drill a shallow hole into the board. This is particularly necessary when working with hardwood. In softwood, you can usually drive the screw head flush without first countersinking the board.
Now, if you want to set the screw head below the surface, you’ll need to drill a counterbore hole using either a small-diameter spade bit or brad-point bit. Counterbore holes can then be covered with wood plugs (and sanded flush) or decorative wooden buttons.
6 Use a Combo Bit
As mentioned above, you can use individual bits to drill all the necessary holes prior to driving in the screws, or you can use a combination bit. With this single timesaving tool you can bore the pilot hole, screw-shank clearance hole and countersink or counterbore—all in one motion. Combination countersink bits come in various screw sizes (typically 4, 6, 8, and 10) and are sold individually or in sets.