Drill bits are used to make different sized holes in various types of materials, so it's important to know which bit is best for your project. Using the wrong bit can not only damage the substrate and tool itself, but it can also lead to injury. It's important to understand which drill bits you need for your project before making a purchase.
Understanding Drill Bits
For starters, the shank is the bit's end that stays secured in your drill's chuck. There are three basic types of shanks.
Straight shanks are round and are held in a 3-jaw chuck by the friction from tightening it. These shanks have very accurate centering.
These can be held in a 3-jaw chuck for quick removal and insertion, but they are not as accurate as straight shanks.
Slotted Drive Systems (SDS)
Slotted drive systems require an SDS chuck and are great for hammer drilling. They have high torque transmission and can be chucked with one hand, but they're not very accurate when centering.
The shank is connected to the drill bit's shaft and ends at the point. When deciding on a bit, remember that flatter points are better for harder materials and may require a pilot hole to get started. It's also important to know that a drill bit's size refers to the diameter of its body, but most bit sets have the sizes commonly needed for most jobs.
Drill Bit Materials
The material that a drill bit is made out of determines its lifespan and degree of functionality, so make sure that the one you're using is suitable for the material that you're drilling into. Here are some common drill bit materials and the types of jobs they're good for.
High speed steel (HSS) drill bits consist of strong tool steel, which makes them inexpensive and very common. These highly versatile bits are great for:
- Soft metals
- Polyvinyl chloride (PVC)
Black oxide-coated HSS bits resist rust and corrosion better than HSS bits, and they're 50% more durable. Use these bits for:
Cobalt drill bits are made of a hardened steel alloy that quickly dissipates heat. Since the friction from drilling into hard metals creates so much heat, these bits are the ideal choice for:
- Cast iron
- Stainless steel
Titanium-coated bits are sharp and harder than cobalt bits. They also dissipate heat even more quickly than cobalt bits and are the best choice for general production work. The tip must be recoated with titanium nitride (TiN) when it becomes dull, but it's usually cheaper to just replace the bit. Titanium nitride-coated bits are suitable for most:
Carbide-tipped drill bits are very tough and only suitable for specialty jobs that require drilling into extremely hard materials. Therefore, they should not be used in most hand-drills and drill-presses. The most common applications include:
Drill Bit Types
Twist bits are the most common type of drill bit out there. They have three or four spiral flutes wrapping around the body to channel drilled debris (called swarf) out of the hole. It's usually best to create a pilot hole before using these bits. Twist bits are designed to cut metal, but they can be used to drill into most materials. Remember that drilling into wood requires a sharp point that has not previously been used to drill metal.
Brad point bits
These bits have a sharp tip that allows for exact hole positioning. They also make cleaner holes because of their precise edges. Brad point bits are great for drilling through-holes and pocket-holes into both hard and soft woods. This precision and cleanliness makes brad point bits the ideal choice for woodworking.
Auger bits have a spiraled, corkscrew point that twists into the substrate before the rest of the bit for greater accuracy. This makes drilling easier since significantly less pressure is required to bore an accurate hole. Auger bits typically have larger-than-average fluting to efficiently clear swarf and will usually have a hex shank to increase chuck's hold. These bits produce clean and precise holes in hard and soft woods.
Also called paddle bits because of their wide and flat blade that sits below the point, spade bits are most commonly used to drill quick holes that don't need to be too clean or precise. Spade bits are commonly used by electricians and plumbers to drill holes that won't be seen after a project is finished. They can be used in woodworking, but it's important to remember that the exit hole may be blown out and splintered. Spade bits won't dissipate swarf and cannot drill very deeply.
Self-feed bits have a corkscrew point that makes digging into wood quick and easy. They're great for creating holes in wood for pipe and conduit. The bit's teeth must be kept sharp for safety and efficiency; sharpening should be done periodically with a file.
These are essentially twist bits that have a hollow center to run wire though. They can be up to 18 inches long and can be used to drill through most common building materials. Once the hole is drilled and the wire put though the bit, it is drawn back to run the wire though the hole.
Forstner bits were patented in 1874 and were a revolutionary gunsmithing and woodworking tool. They are great for cutting overlapping holes, pocket-holes and notches on workpiece edges. Forstner bits cut cleanly and precisely, which makes them ideal for cutting holes for dowels. Hand drills may not provide the force needed to operate these bits, so they are best used on a press.
Hole saw bits
These are ideal for cutting holes that are larger than one inch in diameter. They usually have a pilot guide in the center to keep the saw teeth from walking. They don't cut the substrate's core like spade bits, which makes them best for larger holes. Hole saws usually have a fairly short aspect ratio which affects how deeply they can drill, and the drill being used must produce high torque at low speeds.
Countersink bits are used to create a conical hole in a material so that bolts, screws or rivets can fit flush within it. They are also used for deburring.
Step bits are designed to drill into thin metals and may be used with wood. Their diameter is stepped, which makes it possible to drill different-sized holes with the same bit. Step bits can also be used for deburring.
Tile bits have special tips that make it possible to drill through hard materials without cracking and splintering them. Carbide-tipped drill bits are best used with ceramic tile while diamond-tipped bits should be used on porcelain and glass. Use a medium speed and steady pressure to avoid wearing out and overheating the drill bit.
These are used for cutting holes in brick and stone. If your substrate is concrete, make sure you have a bit that is designed for that application. Drilling into masonry is a high-impact process that can break most drills, so it's best to use a hammer drill with a masonry or concrete drill bit.
These bits are ideal over hand tools because they increase efficiency while decreasing fatigue. Most cordless hand drills are intended to be used as screwdrivers, which is why they have various speed settings.
Coring bits are like hole saws in that they utilize a saw-toothed ring to cut a hole that preserves the core, but they are usually water-cooled and used in more heavy-duty applications.
Drill Bit Maintenance
Making sure you're using the right drill bit for the job is the best way to ensure the life of these tools, but there are a few other things that you can do to take care of them:
- Let the bit cool down after drilling
- Clean the bit and brush away any swarf
- Apply a small amount of machine oil periodically
- Regularly inspect the bit for damage
- Keep bits' points sharp (or replace dull bits)
- Store bits in a cool, dry place
- Store bits in plastic sleeves (or a specific case) to prevent abrasion from other tools
Always make sure you're using the right drill bit for the job and consider using depth stops, bit holders and drill extensions to make things easier. Finding the right bit to use takes a little bit of study (and perhaps trial and error), but once you know your bits, projects become much easier.
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