When we need to drill metal, we can use a cobalt drill bit which is compatible with so many metals such as aluminum, bras, steel, stainless steel, titanium, cast iron, etc. When a cobalt drill bit is used to drill metal, it should have a proper cutting angle and cutting speed in order to have maximum efficiency.
Cobalt drill bits are good for many alloy and non-alloy metal drilling tasks. The cobalt drill bit point angle should be between 135 – 140 degrees for the metal. You can use 2000 – 2500 RPM for small cobalt drill bits and 600 RPM for larger drill bits up to 1/2″. Always use a liquid coolant for heat dissipating and lubricating the drill bit and material.
When you drill metal using cobalt drill bits, you can use higher RPM than other drill bits with a little bit of thrust. But it depends on the hardness of the workpiece.
Are Cobalt Drill Bits Harder than Metal?
Usually, cobalt drill bits are harder than many metals. Obviously, when drilling, the drill bit’s hardness should be higher than the material’s.
It’s a simple fact. But when using a drill bit with an unnecessarily high hardness on something soft like plastic, the high temperature caused by the plastic may melt and stick to the drill bit and cause damage.
Surface wear and abrasion resistance are properties influenced by the metal’s hardness. A material’s ductility and hardness impact its capacity to withstand denting due to impact. Tempering is a heat-treatment technique used to increase the hardness of numerous metals, including those that have been cold-rolled and cold-worked.
So let’s find out about the hardness of the material and the cobalt drill bit. Let’s look at the Rockwell hardness scale (HRC).
| Metal | Hardness Rockwell B Scale |
| Aluminium | 20-60 |
| Copper | 10 |
| Commercial Bronze | 42 |
| Jewelry Bronze | 47 |
| Steel | 60 |
| Cast Iron | 65 |
| Stainless steel | 70 |
| Cobalt | 70 |
| Titanium | 74 |
What Metals Can Be Drilled Using Cobalt Drill Bits?
According to the above chart, it is clearly visible that lower hardness metals such as aluminum, copper, bronze, steel, cast iron, stainless steel, and titanium can be drilled (M42 cobalt drill bit) using cobalt drill bits.
Cobalt drill bits can be used on both soft and hard metals efficiently. Below guide will help you to drill both soft and hard metals using cobalt drill bits.
Types of Cobalt Drill Bits for Metals
Cobalt drill bits are a combination of steel or another alloy mixed with a small percentage of Cobalt. According to the type of building material, there are two distinct varieties of Cobalt drill bits.
- M35 Cobalt drill bits
- M42 Cobalt drill bits
Depending on the drill bits’ size and shape, there are also other types that one can consider.
M42 contains 8% Cobalt in addition to steel. It is highly resistant to high heat. According to that, the melting point of the M42 is 2853 oF. Therefore, it was highly recommended for the drilling of hard materials and metals.
M35 contains 5% Cobalt in addition to steel or steel alloy. Therefore, it is also highly resistant to high heat. The melting point of the M35 is 2723oF.
In addition, coated cobalt drill bits can buy from the market. In-depth guide about M35 and M42 Cobalt Drill Bits.
Cobalt Drill Bit Angle For Metals
The drill bit angle is a very important factor in the drilling process. Normally, we use 118 degrees for soft metals and 135 for hard metals with respect to cobalt.
The drill bit angle is a major factor in cutting speed. When the drill bit angle is wide, it can cut the material aggressively. As a result of this, chips will remove fastly, and it will penetrate inside the material quickly. A narrow cutting angle is always good for soft metals such as aluminum.
Cobalt drill bits can have a wider cutting angle of 135 – 140 degrees, which is highly recommended for harder metals such as titanium. Due to the wider cutting angle, it slowly drills inside the workpiece. Hence you should use a lower RPM always.
If you use a narrow cutting angle drill bit on harder metal, it will overheat instead of drilling.
Cobalt Drill Bit RPM and SFM for Metals
when you drill using cobalt drill bits, you can use 2000 – 2500 RPM for the smaller drill bits, such as 1/8″. When you use larger drill bits up to 1/2″, you can use lower RPM such 600 RPM always. You can check suitable RPM values for aluminum, brass, bronze, mild steel, cast Iron, and stainless steel here.
- R.P.M. = (3.8197 / Drill Diameter) x S.F.M.
- S.F.M. = 0.2618 x Drill Diameter x R.P.M.
Coated Cobalt Drill Bits For Metals
Cobalt drill bits usually do not have an external coating. As a result, such cobalt drill bits can be re-sharpened. But such a coating has some additional advantages.
Those may;
- Good lubricity,
- Having less friction between the material and the drill bit,
- Low heat resistance and extended tool life.
| Type of coating | Reasons | Result |
| TiN | ➤ To increase the surface hardness of the bit. ➤ To provide a thermal barrier by reducing friction. | ➤ Increased production rates. ➤ Increased corrosion resistance. ➤ Three to six times longer tool life. |
| TiCN | ➤ To boost the strength of the drill bit. ➤ To resist wear and tear, even at high speeds. | ➤ Makes drill bits heavy-duty, durable, and ➤ last longer than a standard drill bit. |
| TiAlN | ➤ To boost the strength of the drill bit.To resist wear and tear, even at high speeds. | ➤ Extended the life of a tool by four or five times. |
Conclusion
Cobalt drill bits are highly recommended tools for metal drilling. Although it is a bit expensive, its service life is higher. Using a cobalt drill bit, you can have a lower cost per hole during its service life. When you drill soft metals such as aluminum using cobalt drill bits, you can use high RPM with a lower cutting angle. But for the hard metals, you should have a wider cutting angle and lower RPM always.
