How to Choose the Right Metal Drill Bits for Steel & Aluminium?

Drilling metal is an essential process for many industries, from heavy machine manufacture to home metalworking projects and everything in between. It can sometimes be difficult for non-professional metalworkers to drill metal, especially when not using the correct drill bits.

In this article, we’ll look at which bits are right for drilling metals, particularly steel and aluminium.

Types of Metal Drill Bits for Steel & Aluminium

There are three main drill bit types used on metals such as aluminium and steel:

• High-speed steel – the most common type of drill bit material and the cheapest to buy
• Cobalt – an alloy of high-speed steel with better hardness and cutting speed
• Carbide – high-performance drill material often used in machining

HSS vs Cobalt vs Carbide Drill Bits: Which Is Best for Your Metal?

Carbide drill bits can drill faster, have high resistance to wear and should last longer, but only if they are used correctly. They usually work best with machine tools such as pillar drills or milling machines.

HSS bits are much cheaper and can still cut at acceptable rates but are worse for harder materials such as certain alloys of steel. They are, however, quite accommodating to less than ideal drilling conditions.

For general use and to keep around the shop or in your toolbar, Cobalt drills probably offer the best combination of resilience, cutting performance, and cost.

How to Choose the Right Drill Bit for Steel

The most important factor when selecting a drill bit is the type of material; mild steel can be drilled easily with regular HSS bits, but harder materials such as alloys and stainless steels are best suited for cobalt or carbide bits.

Also consider how the parts are going to be drilled and how many holes are needed. If the only option is by hand, using a battery or corded drill, cobalt is the best option, as it is both hard and tough, whereas cobalt bits can easily break if the drilling angle is not perfect.

However, if thousands of holes need to be drilled, and the parts can be drilled with a solid setup in a mill or drill press, then carbide bits are the best option for high performance.

Best Drill Bits for Aluminium: Preventing Clogging & Clean Cuts

Cobalt or HSS drill bits are perfect for drilling aluminium, it is a very soft metal, so extremely hard bits such as carbide are usually not necessary. Titanium coated bits can sometimes be preferred, as they help lubricate when cutting soft metals.

To avoid the drill galling, clogging or having aluminium stick to it, use short bursts, known as peck drilling, to clear the cut chips away from the hole and a light cutting fluid – some machinists swear by kerosene. WD40 can help in a pinch.

Drill Bit Sizes, Coatings & Point Angles Explained

Drill bits come in all sizes, from micro drills at #80 (0.3mm) all the way up to 4” and above, for specialist applications.

Many coatings are available for metal drill bits, these are used to improve specific properties of the drill in specific materials, such as being able to resist the high temperatures that come from drilling extremely hard materials. Some common drill bit coatings include the following:

• Titanium nitride TiN
• Titanium Aluminium Nitride TiAlN
• Aluminium Titanium Nitride AlTiN

In general use drills, the most common point angle is 118°. This gives a good combination of cutting-edge engagement and wear resistance. For soft materials like aluminium or plastic, a sharper angle is often used, and vice versa for hard metals.

Pro Tips for Drilling Metal Safely & Efficiently

Drilling can be a dangerous and time-consuming task, especially if not done correctly. Here are some top tips:

• Wear appropriate protective equipment
• Use the correct drill type for the material
• Make sure the bit is sharp
• Use the correct speed and pressure/feed rate for the material
• Don’t allow the drill bit to “rub” on the cutting face, this can lead to overheating
• Make a jig or pattern for repeating holes
• Clear swarf/chips away from the work area to prevent grabbing