Drilling precise, large-diameter holes in a fine woodworking project can be challenging if you have to do it with a handheld power drill or cordless drill rather than using a more precise drill press. Since the throat on the chuck of a handheld drill is smaller (typically 1/2-inch or less) than the chuck on the drill press, there is a more limited selection of twist bits available. Additionally, when drilling with Forstner bits—the very best choice for precise woodworking—a drill press is much more precise (and safer choice) for powering the drill bit, since it keeps the bit at a perfect 90° angle to the workpiece.
Auger bits, such as the Bosch NailKiller bits, are another option, but they can be overkill unless you are drilling through some deep stock. Auger bits require a drill with a good amount of power, they can be difficult to wrestle, and they can leave a pretty rough hole behind. Hole saws can also get the job done, but they're slow and removing the plugs from the bit can be a challenge.
Fortunately, for normal drilling of holes up to 1 1/2 inch in diameter, there is a good alternative: spade bits.
Spade Drill Bits
Also commonly known as paddle bits, spade bits are wide, flat-bladed bits. They are commonly used by tradesmen such as electricians and plumbers for drilling holes in studs in walls for running wiring or pipes (auger bits and hole saws are also used), but they also have a place in the woodshop for drilling on fine woodworking projects.
Spade drill bits are basically flat, broad bits with a pilot point attached to a 1/4-inch diameter shank that can be chucked into both regularly-chucked drills and quick-chuck impact drivers. Each edge of the flattened portion of the bit is sharpened, and the bottom corners of the sharpened area may have a pointed tip, depending on the style and brand of the bit. As the bit is turned by the drill motor, these two sharpened bottom edges will dig into the wood stock around the center pilot point, shaving wood out of the hole in a corkscrew-like manner. If the cutting edges of the bit are particularly sharp, very long shavings are sometimes produced by the drilling action.
How to Use a Spade Bit
A spade bit is relatively easy to use, but unlike a twist bit, which is somewhat forgiving, it is important for the shank of a spade bit to be perpendicular to the workpiece while drilling. To use a spade bit:
- Mark the center point of the hole to be drilled on the wood, and chuck the shank of the bit into the drill.
- Align the point of the pilot tip of the spade drill bit with the mark on the wood, and adjust the angle of the handheld drill so that the shank of the bit is square and perpendicular to the surface of the wood. if you're using a drill press, the bit's angle should already be square to the surface of the wood, unless your drill table is not square to the motor.
- Depress the trigger of your drill slightly to engage the motor and turn the bit slowly. Hold the drill as still as possible so that the pilot point stays aligned with the mark on the wood. Because pilot tips can often "walk away" from the intended center point of the hole, some woodworkers will drill a small pilot hole using a small-diameter twist drill bit and then proceed with the spade drill bit's pilot tip positioned in the pilot hole.
- Once the pilot tip is in place and engaged with the wood, increase the speed to drill the large-diameter hole. Continue drilling until you reach the opposite side of the wood and the bit pokes through to complete the hole.
- When the full width of the bit emerges on the back side of the workpiece, slow the speed of the motor and carefully extract the bit.
One common issue with spade bits is that they tend to splinter and "blow out" the back side of the hole. This blow out can be quite unsightly on a fine woodworking project. There are several methods for drilling clean holes with a spade bit, including clamping a sacrificial board to the back side of the workpiece when drilling; or drilling partway through the workpiece until the pilot point penetrates through the wood, then reversing the board and completing the hole by drilling from the back side.