The materials from which bits are manufactured and the finishes applied to them play a significant role in the life and performance of the bit. Common materials and finishes:
For a typical drill bit, the angle of the point helps determine what type of material the bit can drill. Flatter points â€” such as those with 135-degree angles â€” are suited for drilling into harder material. They may require a pilot hole to keep the bit from wandering. Bits with steeper points â€” such as those with 118-degree angles â€” are suited for softer material. They stay on center better and produce cleaner entry and exit holes. Bits with split-point tips improve drilling accuracy by keeping the bit from wandering when you begin to drill.
Bit size reflects the diameter of the body. Some projects call for specific drill bit sizes, but a set that includes bits from 1/16 inch to 1/4 inch will handle many jobs around the home and workshop. You can add larger bits â€“ 5/16 inch, 3/8 inch, 7/16 inch and 1/2 inch bits if you need them.
The chuck on a hand drill or drill press secures a drill bit to the tool along the bit’s shank. A smaller drillÂ for work around the houseÂ typically has a 3/8-inch chuck.Â More powerful drills for heavier applications have a larger, 1/2-inch chuck. Drill pressesÂ also have larger chucks â€”Â 1/2-inch or 5/8-inch, for example. The bit shank size must not exceed the chuck size of the drill. A larger bit may have a reduced shank â€” a shank with a smaller diameter than the body of the bit â€” allowing you to use it with smaller chucks.
A twist bit is the most common type of drill bit for home use.Â It works for general-purpose drilling in wood, plastic and light metal.
A brad-point bit is designed for boring into wood. The bradÂ at the center of the bit tip helps position the bit precisely for accurate drilling and produces a clean exit point in the workpiece. The flutes â€” grooves that wrap around the bit and channel away chips and dust â€” are extra-wide to remove more material.
An auger bit, another type of wood-boring bit, has a screw tip that starts the hole and pulls the bit through the workpieceÂ toÂ quickly create a clean hole. As with the brad-point bit, large flutes help remove chips and dust. An auger bit with a hollow center provides even more chip removal, allowing for deeper boring;Â one with a solid center is stronger and more rigid.
An installer bit is a specialized twist bit designed for installing wiring, such as that for entertainment or security systems. The bit can drill through wood, plaster and some masonry. Once you drill through the wall, floorÂ or other work surface, you insert a wire into the small hole in the bit andÂ use the bit to draw it back through the hole you bored. You can then attach this wire to additional wire or cable and pull it through the hole.
A self-feed bit bores through wood. Like the auger bit, a screw at the tip helps position the bit and draws it through the work piece. It doesn’t have the standard flutes of a twist bit, so you need to pull the bit back periodically to clear away chips and dust.
A spade bit bores large-diameter holes â€” up to 1-1/2 inches in diameter â€” in wood. It has a flattened blade with a sharp point that helps position and steady the bit. Some spade bits have points at the two edges that help create a neater hole and exit point.
A Forstner bit bores smooth, clean holes in wood. You can use it to create flat-bottomed holes â€” such as for receiving dowels. If you need to bore through the workpiece, it creates a neat exit hole. A point allows you to position the bit precisely on the workpiece. Pull the bit out regularly to clear away chips and dust as you work. A hand-held drill typically won’t give you the force or control you need to use a Forstner bit, so a drill press is a better option.
A hole sawÂ drills large holes â€” such as for installing door hardware or creating a pass-through for wiring.Â A hole saw creates a plugÂ of waste material; a cut-out in the side of theÂ saw cylinderÂ allows you to pry it out. Typically aÂ hole saw attaches to an arbor or mandrel which includes a shank. The arbor also holds a pilot bit for centering and steadying the cutting blade. Some smaller hole saws have a built-in shank and don’t use a pilot bit.
A bi-metal hole saw cuts through wood and metal. A hole saw with a carbide edge works on heavier materials such as ceramic tile and masonry. A hole saw with a diamond edge also works on tile and masonry, but cuts faster than carbide models.
A countersink bit â€” also called a screw pilot bit â€” is a specialty bit for drilling in wood. In a single action, the bit can drill pilot, countersink and counterbore holes, allowing you to countersink a fastener and install a plug over the fastener head.
A plug cutter bores holes in wood, creating wood plugs for use in concealing recessed fasteners.
A step bit is designed primarily for drilling in thin â€” up to 1/4 inch â€”Â metal, but will work with wood. The stepped design allows you to use a single bit to drill holes with different diameters. Often the diameter of each stepÂ is etched into the bit. You can also use this type of bit to deburr holes,Â clearing away waste material.
A glass and tile bit uses a carbide tip to drill into glass or tile while reducing the chance of chips and cracks.
A masonry bit drills into tough materials such as concrete, brick and other masonry. Some work with a standard corded or cordless rotary drill, but those designed for use with a rotary hammer or hammer drill can bore into masonry more effectively. The hammering action of the tool drives the carbide tip into the material while the rotating action channels away debris along the flutes.
The larger the bit, the more torque it carries when spinning. Clamping down your workpiece â€” particularly when using Forstner bits and hole saws with diameters of 2 inches or more â€” helps prevent the bit from spinning it out of control.
In addition to more common drill bits, there are other options and accessories:
Drill saw bits cut irregular holes and contours in wood and metal.
Pocket hole bits are stepped-diameter bits included with pocket hole jigs. They allow you drill angled holes that accept screws for making wood joints.
Scaling chisels work in rotary hammers or hammer drills for chiseling, scaling and chipping masonry.
Extensions extend a drill’s reach.
Depth stops prevent drilling beyond a predetermined depth.
Driver bits and bit holders work on a drill / driver to install or remove fasteners.
Screw or bolt extractors work with a reversible drill / driver to back out damaged fasteners.
Right-angle attachments let you drill and drive in areas where a drill won’t fit.
Drill / driver bit sets collect various sizes and styles of bits in a convenient case.
High-speed steel bits, sometimes called HSS drill bits, are made of an extremely hard carbon steel that has a higher heat resistance than high carbon steel. This allows them to be used at higher drilling speeds, and insures that the bits maintain their structural integrity longer. HSS bits can be coated to improve certain features, and their porous surface holds coatings well.
Carbide tipped drill bits are specialized tips on hardened steel bits. Carbide tipped drill bits have the ability to dissipate heat rapidly, and so will hold an edge longer and tolerate heat better than other drill bit options. Unfortunately, carbide tipped bits are very brittle and will chip if they are not handled with care. They are appropriate for drilling hardwood and thin metals.
Cobalt drill bits are extremely hard and are useful in boring into material too hard for standard high-speed drill bits like stainless steel and other thicker metal surfaces. Cobalt is less susceptible to heat damage than any other drill bit type, but it is also extremely brittle and prone to accidental damage.
Black oxide is the most basic and inexpensive coating. It is commonly used on high-speed steel bits and provides a higher level of heat resistance and improved lubrication. It also protects the bit against water damage, rust, and corrosion.
A titanium nitride, sometimes called TiN, coating reduces friction during drilling and increases heat resistance. Coating a drill bit with titanium nitride can increase the life of the bit up to 5 times. It also allows for faster drilling speeds.
Titanium aluminum nitride, sometimes referred to as TiAIN, is designed to increase the hardness and temperature resistance of the bit. Bits with a TiAIN coating are heat resistant up to 800 degrees Celsius, and cling well to a variety of base bit types.
Zirconium nitride strengthens brittle drill bit types and decreases friction. It is an excellent coating for drill bits that will be used for precision drilling. It is also effective at reducing the risk of accidental damage on brittle bit types caused by rough handling and basic wear and tear.
Specialty bits are made of rarer materials and often have a specifically designed shape that makes them perfect for a certain project. These bits are generally more expensive and harder to find than more traditional drill bits.
Tungsten carbide bits are extremely expensive and extremely brittle. This material is only used to make very fine drill bits. Typically tungsten carbide drill bits have a diameter of less than 1 mm. They are useful in small space drilling situations, and are hard enough to withstand the wear and tear of drilling through abrasive materials.