Buying guide for Best metalworking drill bits
Trying to work out which drill bits are best for metal can be confusing. While designs are largely similar, a number of materials and coatings are used in their manufacture.
A lot of the problem stems from the fact that the metals you might drill vary considerably in terms of hardness. For example, a drill bit capable of making a hole in aluminum might hardly put a scratch on steel.
Durability and price are also important to consider in deciding which metalworking drill bit set to buy.
Key metalworking drill bit set features
Metalworking drill bit materials and coatings
High-speed steel (HSS): The most common drill bit material, it is relatively hard, affordable, and easy to manufacture in different forms. As a result, it is used for all kinds of cutting tools. Several of the other types of metalworking drill bits also have HSS at their core.
HSS is great for drilling wood and plastic, and it can also drill through non-ferrous metals (those that don’t contain iron) such as aluminum and brass. However, HSS is softer than other drill bits for metal and wears quickly.
Tungsten carbide (often just called carbide): This is a tungsten-and-carbon composite fused to a HSS core to increase drill bit hardness. Carbide drill bits can produce acceptable performance in non-ferrous metals, but while popular for masonry drills, the material is not often used for metalworking drill bits.
Black oxide: This coating is created by a chemical reaction between high-speed steel and sodium at high temperatures. The resulting drill bit can be 50% harder than HSS. Black oxide drills are a good general-purpose choice, capable of efficient drilling of a wide variety of materials, including non-ferrous metals.
Titanium (or TiN, titanium nitride): This is another form of coating applied to a HSS drill bit. It is technically a ceramic, rather than a metal. Like carbide and black oxide, it increases the drill bit’s hardness. Titanium also reduces friction between the drill bit and the material being drilled, so it offers good heat dissipation — and, since overheating is a major cause of wear, greater durability. Titanium drill bits can drill both non-ferrous and ferrous metals (steel and cast iron).
A note of caution: Titanium drill bits are often gold in color. However, cheap sets sold as metalworking drill bits might have gold plating but don’t actually contain any titanium nitride. Buy from recognized brands to avoid disappointment.
Concerns with coatings: The main drawback with tungsten carbide, black oxide, and titanium is that each is a coating. Resharpening is possible, though the coating will eventually wear through, leaving only the HSS core. Often, these drills are considered disposable.
Cobalt: These drill bits are not coated, but are formed as an alloy. So cobalt is added to HSS during production. As a result, cobalt creates the most durable metalworking drill bits, capable of being resharpened over and over again.
There are two types of cobalt drill bit: M35, which contains 5% cobalt, and M42, which contains 8% cobalt. The latter is harder but is also more brittle, so M35 is more common.
Cobalt undoubtedly produces the best metalworking drill bits, capable of drilling both non-ferrous and ferrous metals. However, it comes at a premium price. Professional woodworkers will probably want to make that investment, but do-it-yourself users will often find one of the other options perfectly adequate.
Metalworking drill bit shapes
- Twist-drill bits: Most metalworking drill bits follow a fairly standard twist-drill pattern with two flutes running down the sides to help clear waste. Tip angles can vary. A 118° angle is probably the most common, and it is considered optimum for non-ferrous metals. Bits for drilling ferrous metals may have a 135° or 140° angle.
- Stepped drills: These offer versatility when drilling thin sheet material. Each drill bit can contain between 6 and 12 different cutting diameters, in ever-increasing steps. It’s important to check the depth of each step, as this defines the maximum thickness of the sheet it is capable of drilling.
- Hole saws: Hole saws are most often used for wood or masonry, but tungsten- and titanium-tipped models are available for cutting metal. They offer much greater diameters than twist or stepped drills, but depth of cut is restricted. Hole saws come in two forms. Some have a toothed ring, while others also have a small diameter twist drill in the middle. The middle ring helps position and guide the larger-diameter outer ring. Without it, hole saws can wander dramatically, so a drill press would be needed.
- Milling machines: Even with hole saws available, the largest-diameter metalworking drill bits are seldom much more than an inch. To produce larger-diameter holes in metal of any thickness, particularly the various types of steel, you need to use a milling machine.
Metalworking drill bit sets
Metalworking drill bit sets vary enormously, from those that contain a half-dozen bits to those that offer over 100. The variety of hole sizes you need to drill on a regular basis will largely define which is most appropriate for you.
Occasional do-it-yourself users will probably find a 15- or 20-piece set that contains all the variety they need, and it may be the only set they ever purchase. However, for regular users and contractors, larger sets do frequently offer a better bang for the buck. They often contain more than one of each size, meaning there’s always a spare handy should a drill bit break.
FOR YOUR SAFETY
Always wear safety glasses or goggles when doing any kind of drilling. Small metal fragments, called swarf, are very sharp.
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Accessory
Drill bit sharpener: Drill Doctor DD350X
It is possible to sharpen drill bits using a bench grinder, but a lot of skill is required to maintain the best angle. The Drill Doctor is quicker and easier, and it uses a diamond wheel to sharpen high-speed steel, carbide, black oxide, titanium, and cobalt twist drills. It can also sharpen masonry drills. It does not sharpen stepped drills or hole saws.
While many powerful hand drills offer sufficient performance to drill metal, where practical, a drill press provides greater control and accuracy.
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Pricing
Inexpensive
If you only need to drill aluminum or brass on an infrequent basis, HSS drill bits will do the job. There are 20-piece sets available for under $20.
Mid-range
Black oxide and titanium drill bits cost a little more. Again using a 20-piece set as a guide, expect to pay between $20 and $30.
Expensive
Cobalt drill bits attract a premium price. For a 20-piece set, you could pay anywhere from $30 to $80. Much depends on the type of cobalt. The number of drill bits also has a big impact, and professional sets can cost hundreds of dollars.
DID YOU KNOW?
When drilling metal with a hand-held drill, never use hammer action. It will create a ragged hole and can damage the drill bit.
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Tips
- Make a guide. Drilling metal is not as easy as wood or plastic. With wood or plastic, the drill bit will start to bite as soon as you apply pressure, helping keep it in place. That won’t happen with metal, so the drill bit has a tendency to wander. To prevent this, create a small indentation using a hammer and a center punch.
- Or a pilot hole. For large holes, first drill a small hole called a pilot hole. It is easier to maintain accuracy, and since you’ve removed some material, the larger drill bit will run cooler.
- Secure it. Use a drill press with a vise, or clamp the workpiece securely if drilling by hand. It is both safer and more accurate.
- Slow it down. People often think the maximum possible speed needs to be used to drill metal. This is not the case. Slowing the drill down helps prevent overheating, and the bit will cut more efficiently.
- Deburr it. Drilling metal creates a “burr” on the underside of the workpiece that’s jagged and can result in a nasty cut. Take a larger diameter drill bit or countersink, and twist it around the hole manually to carefully cut away the excess. This is called deburring.
FAQ
Q. Is cobalt stronger than steel?
A. Cobalt on its own is very hard, but brittle. However, when cobalt is added to steel, the resulting drill bits are much better at drilling metals than steel alone.
Q. What is the best drill bit for aluminum?
A. Low-cost HSS drill bits are capable of drilling aluminum, but they wear fairly quickly. Tungsten-carbide tipped, titanium, and cobalt are all more efficient.
Q. Can I use metalworking drill bits for wood?
A. Yes. The drill bit pattern is usually the same, so drill bits for metal are equally good at drilling wood.
