If you need to drill a hole, it seems like a simple matter to grab a drill and a drill bit and go to work. But if you ever check out the aisles of a hardware store you’ll find quite a variety of bits for different applications. Knowing the right one for a specific job will help you get the project done faster, safer, and with better results.
Twist drill bits: These are the bits that do-it-yourselfers are typically the most familiar with. Twist drill bits are usually made of high-speed steel (HSS) and have a flute — a recess in the side of the bit — that spirals up from the point of the bit toward to the top. The flute allows for chip removal as the hole is being drilled. Twist drill bits have a shallow point and are used primarily for drilling metal. They will also work fine for smaller holes in wood and plastic, but their shallow point can cause them to chip the material when drilling larger holes.
Sizes, which refer to the diameter of the bit, commonly range from tiny No. 1 up to 1/2 inch, and larger sizes are also available for some machine shop applications. Sizes above 3/8 inch typically have a shank that is stepped down to 3/8 inch, allowing them to be used in a drill with a 3/8-inch chuck. Twist drill bits are also available with a titanium coating for more abrasion resistance and longer life in metal-drilling applications.
Brad-point bits: Brad-point bits, which look similar to twist drill bits, have a sharp point at the end that makes it easier to align the bit for more precise drilling. Brad-point bits are intended only for wood and have a special cutting edge around the end of the bit called a spur. The spur scribes and cuts the outside diameter of the hole as the bit enters it, greatly reducing splintering and tearing of wood grain and veneer. Brad-point bits are available in both HSS and carbide tips. The carbide-tipped version is more expensive but it will hold its edge quite a bit longer between sharpenings. Brad-point bits are commonly available in sizes ranging from 1/8 inch to 1/2 inch.
Wood-boring bits: For larger holes in wood, drywall and other soft materials, wood-boring bits — also called spade bits — are an economical choice for a good all-purpose bit. Wood-boring bits have a flat cutting head with a point in the center, two angled cutting edges and two cutting tips.
The point centers the bit in the hole, the cutting tips cut the outer diameter, and the cutting edges shear off the rest of the wood. These bits will cut a flat-bottomed hole but have a tendency to tear the wood if used too aggressively. They are available in HSS, carbide-tipped and cobalt-coated, in sizes from 1/4 inch to 2 inches.
Forstner and spur bits: Forstner bits are also intended only for wood, and have a number of uses in woodworking and finish carpentry. A Forstner bit has a round cutting head with a brad point and a cutting spur around the outside edge, attached to a smooth, nonfluted shaft.
The design of the head allows for the cutting of flat-bottomed holes with very smooth sides, and creates and expels "curls" of wood as it drills, somewhat similar to a plane. Since the cutting action occurs around the outer edge of the bit, Forstner bits can be used to drill partial arcs as opposed to complete circles, and also work very well for drilling pocket holes at an angle. …CONTINUED
Spur bits work on the same principle but have multiple cutting teeth on the outer edge for faster cutting with less heat buildup, especially in larger sizes. Forstner and spur bits are available in HSS, carbide-tipped and titanium-coated, in sizes ranging from 1/4 inch to 4 inches in diameter.
Auger bits: Auger bits are used for fast, aggressive drilling in wood, most commonly in applications such as plumbing, electrical wiring, timber framing and boat building. Auger bits have a sharp screw point that draws the bit into the wood, and twin cutting flutes at the outer edge that cut quickly but with more splintering than some other types of bits. Deep flutes draw chips out quickly for cooler, faster cutting. Auger bits are commonly available in sizes from 1/4 inch up to 1 1/2 inches.
Masonry bits: As the name implies, masonry bits are used for drilling into concrete, stone, stucco, bricks, and other masonry. They look somewhat like a standard twist drill bit but have a fairly blunt, carbide-tipped end that withstands the abrasion and high friction associated with drilling masonry. Common sizes range from 1/8 inch to around 1 1/2 inches.
Deep-drilling bits: Many of the bits described above also come in long versions for drilling deep holes. Brad-point bits, for example, are commonly available in 10-inch lengths, and auger bits can be found in lengths up to 17 inches. For really deep holes — such as for running wires and other similar applications, you can find twist drill bits in lengths of up to 36 inches. There are also extensions available for most types of drill bits, allowing you to extend the length of the bit for deeper drilling.
Drill bits are commonly found in home centers, hardware stores, lumber yards and a wide variety of other retailers. Pay attention to the quality of the bit and the price. Stay away from the imported, bargain bits, which dull easily and are dangerously prone to snapping.
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