Start with the material, not the bit
Most drilling problems come from using the wrong bit or the wrong speed for the material. A bit that cuts wood cleanly may skate across steel, and a masonry bit that works in brick will tear up a wood panel. Pick the material first, then the bit geometry, then the coating or alloy if you need one.
Whatever you drill, wear eye protection, secure the work so it cannot spin, and remove the bit’s chips in a way that keeps your hands clear of the cutting edge. Unplug the tool or remove the battery before changing bits.
Drill bits for wood
Wood is soft enough that shape matters more than hardness.
- Brad-point bits have a sharp center spike and two cutting spurs. The spike keeps the bit from wandering and the spurs shear the fibers, which gives clean entry holes. They are a favorite for furniture and joinery.
- Standard twist bits will drill wood adequately, but the point can wander and the exit side may splinter.
- Spade bits are inexpensive and make large rough holes quickly, usually where appearance does not matter.
- Forstner bits cut flat-bottomed holes and clean, large-diameter holes, such as hinge cups. They work best in a drill press at moderate speed.
- Auger bits pull themselves into the wood and clear chips well, so they suit deep holes in thick timber.
To limit tearout on the exit side, clamp a scrap board behind the workpiece. Large bits generally want slower speeds than small ones; a lower tool RPM suits larger bits.
Drill bits for metal
For drill bits for metal, the usual starting point is the twist bit made of high-speed steel, often shortened to HSS. It holds an edge better than plain carbon steel when it gets hot, which is why high-speed steel appears on most metal bits. The surface treatment or alloy on top is where bits differ.
- Black oxide is a dark finish that helps resist rust and reduces friction a little. It is a modest upgrade over bare steel.
- Titanium nitride is a gold-colored coating that can reduce friction and extend life in many general jobs. Once the coating wears off at the tip, the bit behaves like plain high-speed steel, and sharpening removes the coating at the cutting edge.
- Cobalt alloy bits have cobalt blended into the steel itself rather than just coated on it, so they resist heat better and are commonly chosen for tough materials such as stainless steel. They are typically harder and can be more brittle, so avoid side pressure and wobble.
- Step bits cut stepped holes in thin sheet metal and leave a cleaner edge than twist bits, which tend to grab and distort thin material.
Metal drilling needs slower speeds, steady pressure and lubricant. Cutting oil keeps the edge cool and carries chips away. Start with a center punch mark so the point does not wander, and drill a small pilot hole before a large one. Large holes in thick metal are commonly done in stages. Heat is the enemy: if a bit smokes or turns blue, it is overheating and losing hardness. A file will tidy the burr afterward, a step known as metal deburring.
Drill bits for masonry
Brick, block and concrete are drilled with carbide-tipped masonry bits. A carbide insert at the tip is hard enough to crush mineral material. Masonry bits are normally used with a hammer action, where the drill adds quick impacts while it turns. This is the basis of hammer drilling masonry, and heavier work in concrete usually moves to an SDS-style rotary hammer with matching bits.
Use a standard masonry bit in a regular drill for soft brick and mortar joints, and expect it to be slower in concrete. Never use a masonry bit for wood or metal, and avoid forcing it: pressure does not help and can overheat the tip. Clear dust from the hole periodically, and wear dust protection since masonry dust is harmful to breathe. If you are setting fasteners afterward, the hole diameter needs to suit the anchor, which is the job of wall anchors.
Drill bits for plastic
Plastic is easy to cut but easy to damage. It melts when too hot, cracks when too aggressive, and can grab the bit as it breaks through.
- Use a sharp twist bit at a lower speed with light pressure.
- Brad-point bits can crack some brittle plastics, so test on scrap.
- Special plastic-cutting bits and step bits help with thin sheets.
- Back the material with scrap and back the bit out occasionally to clear melted chips.
Acrylic in particular tends to crack when a standard bit bites at the exit, so slow down as the tip emerges.
Glass and tile
Glass and ceramic tile call for specialized spear-point or diamond-coated bits, a very low speed and water to keep the tip cool. Carbide masonry bits used with the hammer feature off can work in some tile, but results vary. Tiles can chip easily, so mark the spot with tape and start gently.
Choosing sizes and sets
A bit set with a range of common sizes covers most household needs, and more specialized bits can be bought individually when a job demands them. Check that the shank suits your chuck. Hex shanks grip well in impact drivers, while round shanks fit most standard chucks. Compare sets by the materials listed, not just the piece count, and note whether the index case is robust enough to keep bits organized.
Keeping bits sharp
A dull bit makes heat instead of chips, needs more force, and produces ragged holes. Signs include squealing, smoke, a rough hole and the need to push hard. Clean bits after use, store them so the cutting edges do not knock together, and sharpen twist bits if you have the skill and the equipment or replace them when they are worn. Cheap bits are fine for occasional light work, but better bits generally cost less per hole if you drill often.