Carbide and cobalt drill bits are often used in applications where high-speed steel drill bits aren’t sufficient. Why is this, and what’s the difference between these two options? How would you know which option to choose?
Difference Between Cobalt and Carbide
Higher-end drill bits are often made of carbide or cobalt. Cobalt bits are made of HSS with cobalt blended into the alloy mix whereas carbide bits are made of sintered tungsten carbide.
Carbide drill bits are generally more expensive than cobalt but can withstand higher temperatures and have greater wear resistance. This leads to longer tool life, often offsetting the cost difference. Carbide drill bits enable greater cutting speed while maintaining a high-quality finish than cobalt drill bits, enhancing manufacturing throughput.
What is a Cobalt Drill Bit?
Cobalt is often incorporated into drill bits made of high-speed steel (HSS) at a 5-8% concentration. This enhances the wear- and heat-resistance of the drill bit, prolonging material life. Unlike a titanium drill bit which is a coating, cobalt is added into the alloy. This allows it to be resharpened without losing the cutting quality of the bit.
Cobalt drill bits are often used on stainless steel, tool steels, and other hard, ferrous materials.
Cobalt drill bit can withstand far greater temperatures than the cheaper bright HSS and black oxide drill bits. They are easily resharpened and usually less expensive than carbide drill bits.
Cobalt drills often have self-centering points. The cost of the drill bit justifies the extra cost of grinding a self-centering point on the bit. This eliminates the need to drill guide-holes, decreasing cycle time.
A cobalt bit can drill up to five times their shaft diameter before requiring peck drilling (inserting the drill bit into the cut multiple times to facilitate proper cutting). This increases tool life since peck drilling dramatically increases tool wear. The most significant amount of tool wear on drill bits occurs when starting a cut. This wear decreases significantly once the drill bit’s tip is engaged with the material. Since peck drilling repeatedly restarts the cut, wear increases markedly.
It can cut soft as well as hard materials. You can use a cobalt bit for drilling both wood and metal.
These bits are also affordable and easily available.
Cobalt drill bits don’t last as long as carbide drill bits, requiring resharpening after more or less every 100 holes drilled in a production environment. These drill bits also can’t work at the drilling speeds carbide drill bits are capable of.
Cobalt drill bits also tend to be brittle. This leads to chipping and other damage when drilling materials that are too hard or attempting to drill at temperatures outside the specified range.
What is a Carbide Drill Bit?
Carbide drill bits are the high-end option in manufacturing and CNC (Computer Numeric Control) environments.
Tungsten carbide is a chemical compound of carbon and tungsten which is in powder form. This powder is joined by a process called sintering to form solid carbide rods and blocks. Often tungsten carbide and titanium carbide are combined with a binder material to produce the industrial-grade carbide. Hence, they are also known as cemented carbide.
The carbide drill bits are capable of high-speed drilling and are often used on hard, non-ferrous heavy metals and fiber-glass reinforced plastics. It is the hardest and most brittle drill bit currently in everyday use.
Carbide Dill Bit Uses
Carbide drill bits are designed for heavy-duty work on the hardest, most demanding materials. These are generally not suited for hand tools such as cordless drills or impact drivers and are generally meant for production drilling. Here, high-quality tool holders and work holding equipment are necessary.
Carbide Bits Pros
Carbide is extremely hard and heat resistant. For this reason, these drill bits are the most chip-resistant.
Since the material is so hard and rigid, it allows coolant through-holes to be cut into the drill bit. Here, the cooling liquid is delivered directly into the cut, efficiently cooling the cutting tip and the actual cutting area. This improves the cut quality in two ways: heat reduction and chip removal. Lower temperatures decrease drill wear and heat treatment of the part being drilled. Faster chip removal enables faster cutting and prevents damage to the cut and drill bit from chip build-up inside the cut.
Carbide drill bits last very long, allowing for roughly 1000-2000 holes to be drilled before it requires resharpening. They can also work at incredibly high speeds, vastly improving cycle times. This decreases manufacturing time, which translates into savings for the manufacturer.
Carbide drill bits also have self-centering tips, which decrease cycle times, as explained previously.
Using carbide bits eliminates the need for peck drilling, dramatically increasing tool life, as explained previously.
Carbide drill bits are costly and cannot be easily resharpened. Unfortunately, carbide drill bits tend to chip instead of wearing evenly.
You need a special tool and cutter grinder with a diamond grinding wheel to sharpen these bits which is a time-consuming process. Thus, they should often be replaced instead of resharpened.
Luckily, the longevity of these tools decreases the replacement frequency.
Is Carbide Harder than Cobalt?
Yes, carbide is harder than cobalt. Cobalt bits have a hardness of approximately 65HRC whereas tungsten carbide has a hardness of up to 75HRC on Rockwell scale. This is the main reason that carbide drill bits tend to outperform their cobalt counterparts.
Why Choose a Cobalt Drill Bit?
Cobalt is a great option when drilling through a variety of hard and soft materials. They can cut through most hard metals, including cast iron, bronze, stainless steel, and titanium. Usually, they can even cut through weld seams.
Cobalt drill bits are the better option in cases where the less expensive high-speed steel drill bits aren’t cutting it. They offer faster drilling speed, last longer, can withstand greater temperatures, and tend to have self-centering tips. This reduces the need for pre-drilling, cutting down on manufacturing time.
Generally, cobalt drill bits are used for industrial applications that don’t require the increased performance of carbide drill bits. These applications generally also can’t justify the costs of expensive carbide drill bits.
When to Go for Carbide Bits?
Carbide is the highest-performing drill bit currently on the market. These are used in industrial applications that require high-precision and long tool life when cutting hardened and tough materials. This is the material of choice when cobalt drill bits aren’t up to the task.
Carbide cutting tools are used on CNC machines for precision, high volume production. Generally, in applications that don’t require extremely high cutting volumes, the expense associated with carbide drill bits isn’t justified. This is because these can easily cost up to ten times what cobalt costs.
Conclusion: Cobalt vs. Carbide Drill Bits
Cobalt and carbide drill bits are both high-performance drill bits. Cobalt drill bits are less expensive than carbide drill bits. Still, they both usually offer self-centering tips, enabling precision drilling.
Cobalt drill bits tend to be better for lower-volume work that involves hardened and tough materials. If you are a hobbyist or even a professional using the drill bits on hand drills or manual drill press, then use cobalt bits. These bits are excellent woodworking, metalworking, and fabrication.
Carbide drill bits are the hardest currently on the market and offer an extremely long tool life. Their excellent hardness also allows them to machine hardened steel. Due to their expense, these are usually chosen in high-volume industrial applications involving high-precision work on hardened materials.