Choose the Right Drill Bit for the Job
One of the most important things when working with drill bits is selecting the appropriate type for the material you’re drilling into. Using the wrong kind of bit can lead to poor results, damaged bits, and even injury. Here’s a quick overview of common drill bit types and their ideal uses:
| Drill Bit Type | Ideal Material | Features |
|---|---|---|
| Twist Bit | Wood, plastic, light metal | Most common type, spiral flutes to remove chips |
| Spade Bit | Wood | Wide, flat blade for boring large holes |
| Auger Bit | Wood | Screw tip pulls bit into wood, deep spiral flutes |
| Forstner Bit | Wood | Produces clean, flat-bottomed holes, boring action |
| Masonry Bit | Concrete, brick, stone | Tungsten carbide tip, specialized flutes |
| Glass Bit | Glass, ceramic tiles | Spear-shaped carbide tip minimizes wandering |
| Step Bit | Sheet metal, thin wood | Incremental sizes for various hole diameters |
Twist Bits
Twist bits, also known as drill bits, are the most common type you’ll encounter. They have a straight shank and spiral flutes that wrap around the body to pull material chips up and away from the cutting tip.
Twist bits are versatile and work well in wood, plastic, and light-gauge metal. For drilling into harder materials like stainless steel, you’ll want to upgrade to a bit made from cobalt steel or other premium materials.
Spade Bits
Spade bits have a wide, flat blade with a centered point and two cutting edges. They are used for boring large-diameter holes in wood more quickly than a standard twist bit. The sides of the blade help keep the bit straight while cutting.
One downside of spade bits is they tend to leave a rougher hole than other types. They also have a tendency to tear out the back of the workpiece as they exit. To minimize this, use a backer board underneath your workpiece or drill in from both sides to meet in the middle.
Auger Bits
Auger bits are another option for drilling deep holes in wood. They have a screw tip that pulls the bit through the workpiece and deep spiral flutes to remove wood chips efficiently. Some auger bit sets include a hollow center to allow removal of the wood plug.
Auger bits are more precise than spade bits but require more pressure to drive them into the wood. They work best in a corded drill or drill press that can maintain consistent power.
Forstner Bits
Forstner bits are designed for drilling clean, precise holes in wood, even at an angle to the grain. They have a circular rim with a sharp edge that scores the wood fibers first. This is followed by a cutting edge that removes a disk-shaped plug of wood as the bit bores into the workpiece.
The unique design of Forstner bits helps them drill flat-bottomed holes, overlapping holes, and angled holes while minimizing tearout. The rim also allows the bit to bore partial holes without a pilot hole. However, Forstner bits do require slower speeds and higher torque than twist bits.
Masonry Bits
For drilling into hard materials like concrete, brick, and stone, you’ll need a masonry bit. These feature a tungsten carbide tip suitable for the abrasive and brittle nature of masonry.
Masonry bits have flutes designed to pull the fine concrete dust up and out of the hole while drilling. Using them requires a hammer drill that combines rotary action with a hammering thrust to pulverize the masonry as the bit advances.
Glass and Tile Bits
Drilling through glass or glazed tiles requires a specialized bit to prevent shattering. Glass and tile bits have a spear-shaped carbide tip that helps prevent wandering and chipping.
To use a glass bit, start by applying firm pressure to score the surface, then reduce pressure and let the bit do the work. Use a lubricant like turpentine and drill at very slow speeds to keep the glass from overheating and cracking. For tiles, use a spray bottle to keep the surface wet.
Step Bits
Step bits, also called unibit bits, are conical-shaped with graduated steps of increasing diameter. They allow you to drill multiple hole sizes without changing bits.
Step bits are commonly used for drilling in sheet metal, as the stepped design helps deburr the edges of the hole as you drill. They can also be used in softer materials like wood and plastic. However, the nature of their design means they drill less precisely than a twist bit.
Use the Right Speed for the Material
In addition to selecting the right type of drill bit, it’s important to use the appropriate speed for the material you’re working with. Drilling too quickly can cause the bit to overheat, break, or burn the material. Going too slowly can cause the bit to bind or snag.
Here are some general guidelines for drill speeds based on material:
| Material | Ideal Speed Range (RPM) |
|---|---|
| Wood | 1500-3000 |
| Aluminum & Brass | 1000-3000 |
| Mild Steel | 600-1000 |
| Stainless Steel | 300-500 |
| Cast Iron | 200-400 |
| Ceramic Tile | 150-300 |
| Glass | 100-300 |
| Masonry | 250-1000 |
Keep in mind these are just general ranges. The ideal speed can vary based on the specific material, drill bit type and diameter, and amount of pressure applied. When in doubt, start off slower and increase speed gradually to avoid damaging the bit or workpiece.
Softening Metal to Avoid Overheating
If you find your bits are overheating or wearing out quickly when drilling metal, you may need to soften the metal first. Work hardening can occur when metal is bent or hammered, making it more difficult to drill through.
To soften steel, clamp the workpiece securely and heat the area to be drilled until it’s red hot, then let it cool slowly. Don’t quench it in water, as this can make the metal brittle. Once softened, the steel should drill much more easily.
Prevent Bits from Slipping
Drill bits have a tendency to slip or walk across the surface when starting a hole, especially on metal or other hard surfaces. This can not only ruin your workpiece, but also potentially cause injury if the drill jerks out of your hands.
Use a Center Punch
One way to keep your bit from wandering is to create a dimple with a center punch. This gives the tip of the bit a place to seat into and helps guide it straight into the workpiece.
To use a center punch, simply place the tip where you want the hole to be and give it a solid tap with a hammer. You don’t need to apply a lot of force, just enough to create a small divot to guide the drill bit.
Use Painter’s Tape
If you don’t have a center punch or need a non-marring solution, try adhering some painter’s tape to the area you’ll be drilling. The coarse surface of the tape gives the bit extra traction to prevent slipping as it starts the hole.
Painter’s tape is also useful when drilling through a finished surface you want to protect. It helps prevent unsightly chips or cracks around the edge of the hole.
Lubricate and Clear Chips for Cleaner Holes
Drilling can create a lot of friction and heat, especially in metal or other hard materials. Properly lubricating the bit and clearing away chips can help your bits last longer and produce cleaner results.
Use Cutting Fluid on Metal
When drilling into metal, using a lubricant like cutting fluid can dramatically improve the process. Cutting fluid reduces friction and heat buildup, helping prevent the bit from overheating and breaking. It also improves the finish of the hole and helps flush away chips.
You can apply cutting fluid by brushing or spraying it onto the bit and workpiece before drilling. Continue to apply it periodically as you drill to maintain lubrication. Avoid using so much that it pools, as this can actually insulate heat rather than dissipate it.
Clear Chips Frequently
The spiral flutes on drill bits are designed to pull material chips up and away from the tip, but they can still become clogged, causing the bit to bind and overheat. This is especially common when drilling deep holes in soft materials like wood.
To avoid this, pull the bit out frequently to clear the flutes of chips. You can also try running the drill in reverse momentarily to dislodge clogged chips. Use compressed air or a small brush to clean the flutes before resuming drilling.
In some materials like acrylic, chips can melt from the heat of drilling and fuse back onto the bit or hole wall. In this case, using a spray lubricant like WD-40 can help prevent chips from adhering.
Drilling Perpendicular and Countersinking
Most of the time you’ll want your holes to be straight and perpendicular to the workpiece. Other times you may want to create a countersunk hole where the screw head sits flush with the surrounding surface. Here are some tips for drilling accurately in these situations.
Use a Drill Guide
For consistently straight holes, a portable drill guide is a handy accessory. It clamps to your workpiece and provides a rigid collar that keeps the drill bit perpendicular as you bore through the material.
Drill guides are available in various sizes to match common bit diameters. Some also offer angle adjustments for drilling at a controlled slant rather than straight down.
Use Scrap Wood Backing
Particularly when drilling completely through a board, using a piece of scrap wood as a backer can help ensure a cleaner exit hole. This is also useful for preventing tear-out when drilling thin stock.
Simply clamp or hold the scrap wood securely behind the workpiece as you drill. The drill bit will pass into it as it exits your material, providing support and minimizing chipping or splintering around the back of the hole. Use a piece thick enough that the tip and flutes have solid material to bite into.
Countersink with a Drill Bit
To create a countersink for a flush screw head, you can use a specialized countersink bit or modify a standard twist bit. To do the latter, mark the depth of the countersink taper on the tip of the bit with a permanent marker. Chuck the bit so this mark is just above the surface of the workpiece, then drill to that depth before boring the rest of the pilot hole.
You can also buy combination countersink drill bits that have a tapered shoulder and a narrower pilot tip in one unit. These are available in sizes to match common screw head types.
Frequently Asked Questions
What causes drill bits to break?
Drill bits usually break from too much speed, pressure, or heat. Driving a bit too hard or fast can cause it to bend and snap, while overheating can soften the metal and lead to failure. Using cutting fluid and clearing chips frequently can help bits maintain their integrity and lifespan.
How do I sharpen a dull drill bit?
While you can buy special drill bit sharpening tools, you can also touch up a dull bit with a bench grinder. First, find the existing angle of the cutting edge. Then, hold the bit against the grinding wheel at this angle, making light contact with each cutting edge until you see a slight burr. Finally, hone the bit by holding it vertically and slightly twisting it as you graze it against the wheel.
Can I use a regular drill bit in a hammer drill?
You should only use drill bits specifically designed for hammer drills in these tools. Standard High-Speed Steel (HSS) twist bits are too brittle to withstand the hammering action and can shatter. Hammer drill bits are made of tougher carbide and have an SDS shank that locks into the special chuck to prevent slippage. If you need to drill into masonry, invest in a set of SDS bits to use with your hammer drill.
What does “TiN coating” mean on a drill bit?
“TiN” stands for titanium nitride, a ceramic coating used on high-end drill bits. The gold-colored TiN coating is harder and more heat resistant than uncoated steel. TiN bits stay sharper longer, resist corrosion, and reduce friction to produce cleaner holes. They cost more than standard bits but can be worth it for frequently used sizes or tougher jobs.
Do I really need to drill a pilot hole?
While you can get away with skipping a pilot hole in some cases, it’s generally a good idea to drill one first, especially in dense hardwoods or when drilling large diameter holes. A pilot hole guides the tip of the larger bit and reduces the chance of splitting the wood. The only time you definitely don’t want to drill a pilot hole first is when using a Forstner bit or spade bit, as their rim-guided design can be thrown off by the smaller hole.
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