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Drill bits are rotary cutting tools used to make holes. They consist of several parts, including the point that makes the first contact with the material being drilled, the cutting grooves or flutes on the drill bit body, and the shank that fits into the drill chuck. The wide variety of different designs, sizes, materials, and coatings used in drill bit construction means careful consideration when choosing the right drill bit for the job. This may be easier said than done, but when drilling into especially hard materials such as stone, glass, or ceramics, you’ll want a drill bit that’s up to the task. In other words, you’ll want a diamond drill bit.
Drill Bit Materials and Coatings
Several different materials are used in making drill bits with different characteristics and appropriate for different applications. High-Speed Steel is the most widespread material, ideally used in general-purpose drilling, such as in wood and non-ferrous metals. Softer materials like plastics and softwoods can be drilled with a low-carbon steel drill bit, but variants with higher carbon content are good for drilling into hardwoods and some metals.
Cobalt steel bits are a step up in hardness and are used on stainless steel and other hard metals. Carbide (or carbide-tipped) variants, such as Tungsten. Boron and Titanium carbide bits, are very hard and often used when drilling into masonry and thicker pieces of metal. Tungsten carbide bits with a polycrystalline diamond (PCD) or Chemical Vapour Deposition (CVD) coating, are the hardest and can be used across all materials. Their high cost though means they’re restricted to specialist use and when drilling into very hard materials.
What Can a Diamond Drill Bit Do?
Drill bits with diamond coatings can open and enlarge holes in different types of materials, ranging from soft to very hard. While they’re usually found on CNC machines and fixed bench drill presses and reserved for industrial uses, diamond drill bits are also good for home usage with corded or cordless drills, particularly when working with ceramics, tiles, or glass. They’re also effective in different types of stone, such as marble, granite, gemstones, minerals, or rocks, as well as bones and shells. And they make easy work of hardwood. While diamond bits are hard and durable, they’re not intended to be used with metals, because of the chemical reaction between the diamond tip and metal surface.
Benefits of Diamond-Coated Drill Bits
Compared to standard HSS or carbide bits, diamond drill bits are not only harder and more durable, they also bring some distinct benefits. They can drill and cut through any material, and do so with little noise, a boon when working at home or the construction site. And they can be used at high speeds and with high accuracy, so speed up workflow and provide consistent results.
There’s also less debris, as the diamond particles cut the materials at a nano level, meaning less dust (particularly with concrete) and no chips or cracks. These drill bits will also outlast all other types, so the high price is offset by the consistent and long-lasting performance. The only downside is that some variants require lubricant or coolant to remove high heat when drilling into really hard materials.
Types of Diamond Bits
Bits can be categorised by the way the diamond coating is applied (and bonds with the tungsten carbide or HSS) into two basic types – sintered and electroplated or bonded. Sintered bits have diamonds directly mixed or embedded in multiple layers onto the bit tip. As the metal tip wears down, a new diamond layer appears. This makes them more durable, and suitable for heavy-duty use on a regular basis. Sintered drill bits are commonly used at higher speeds. They’re the bits to get if you want something that will last, and when performance is more important than price.
A low-cost variant is an electroplated bit, where nickel is used as a bonding agent. Here diamonds are added to the ends of the drill bit tip. While these are durable, the hardness and abrasiveness of the material being drilled will eventually wear off the diamond coating. Electroplated bits are often used at slower drilling speeds and with adequate quantities of coolant. One area where they diverge significantly from their sintered siblings is that they can’t be used on metals. For all other use cases, such as drilling bathroom tiles or when working with glass, electroplated bits are more than capable.
Shapes and Sizes
Diamond bits come in two basic shapes, solid blunt nose, and hollow core bits. Blunt nose bits have diamonds on the tip and the sides of the tip. This type of drill bit is useful when drilling a hole equal to or slightly more than the diameter of the tip. And these are smaller in size, often used at a slower pace, and mostly when working with glass and gemstones.
Core bits are used to drill materials using only the tip edges, and not the entire diameter, in what is known as coring. This process produces a hole the size of the tip and a smaller core or ‘plug’ from the middle of the hole. Core diamond bits are used in harder materials, work at faster rates, and are offered in bigger sizes, ranging from 20 to over 300mm in diameter.
Choosing the Right Diamond Drill Bit
What you end up buying will largely depend on the application, the hardness of the materials drilled, how long you need the bits to last, and what you’re willing to spend. Heavy-duty industrial use calls for sintered bits, while for occasional use such as short-term renovations, or DIY projects, electroplated bits do just fine. Also, consider the hardness of the materials you’re drilling and the size of the hole as bigger and large-diameter diamond bits can get pricey.
