How to Drill Cast Iron

How to Drill Cast Iron?

Cast iron is one of the heaviest and most durable metals on the market. Its characteristics are why cast iron is primarily used to manufacture cylinder pipes, kitchen plates, and automotive parts.

When it comes to drilling this metal, it’s important that you first learn how you can effectively work with it. In the end, not all iron is created equal.

In this guide, we cover how to drill cast iron by teaching you the process in a few simple steps. We also tell you the best way to drill through this stubborn metal and what kind of drill bit is most suitable to use.

Let’s get started!

How Do You Drill a Hole in Cast Iron?

Even though cast iron is significantly harder than wrought iron, it’s more brittle and less malleable.

Cast iron’s compression strength is also remarkable, but it can’t be distorted into different shapes due to its weak tensile strength that doesn’t allow the metal to bend to your liking.

Why are these facts considered essential knowledge? Well, for starters, if you’re planning to drill through cast iron, you need to keep in mind how this metal will react. This way you can choose the appropriate drill speed, bit, and type.

That said, there’s an 8-step, methodic process to drilling cast iron. Below, we go through these phases, one by one, making it easier for you.

1. Diagnose Your Cast Iron

The aforementioned characteristics of cast iron are pretty general, meaning, that most if not all cast iron metals share these qualities.

Since cast iron is a mixed metal, however, these elements will come at different percentages. As such, this will affect what kind of drill bit and drill you’ll end up using.

To be more precise, cast iron isn’t pure as it may contain about 2% to 5% carbon as well as amounts of silicon, manganese, sulfur, and phosphorous.

These different materials cause the cast iron to harden. This in turn means that each piece of cast iron is created differently from the other in terms of hardness.

Simply put, it’s important that you diagnose the features of your cast iron. Make sure to know what type it is too: grey, white, malleable, or ductile cast iron.

2. Clean the Metal

Metal rusts easily, and iron in particular is one of the more susceptible elements to rust. As a result, we tend to stay away from drilling rusty cast iron.

It’s better, instead, to work around it. How? By cleaning the surface you’re planning to drill beforehand.

Luckily enough, it’s quite easy to remove rust off the surface of a cast iron. To begin with, create a mixture using equal parts of white vinegar and water.

Use a soft piece of cloth to apply the solution onto the rusty surface. Remember two things: to rub gently and to avoid coarse wiping material. This prevents further damage to the metal.

Once it’s done, wipe down the debris and move on to the next step. If the rust has only partially come off, try soaking the cast iron in water and vinegar for a few hours.

3. Choose a Fitting Type of Drill

Choose a Fitting Type of Drill

As we’ve gone over before, cast iron is known for its hardness, which means that the drill you’re going to use needs to be able to create a hole in the metal, without a problem.

You may know already that there are many types of drills, including the bench, the hand, and the hammer drill. Since cast iron is a sturdy material, you need a tool with a constant thrust.

With a hand drill, achieving a consistent level of power can be quite hard. Because we don’t want to compromise our efficiency, a bench drill would be a better alternative.

In addition to providing the right amount of thrust to drilling a cast iron, a bench drill is also a safe and accurate drilling tool.

Plus, bench drills typically come with knobs or buttons to adjust their speed and torque, allowing you a variable range of features to work with.

4. Select a Suitable Drill Bit

Selecting a suitable drill bit is the most crucial step of our process. The wrong drill bit can not only damage your expensive drilling tool, but it will damage the cast iron as well.

A golden rule to keep in mind is that your drill bit should be made from a metal that’s harder than the cast iron so it can successfully drill through it.

As such, the following bits won’t be able to drill through cast iron: wood-boring, masonry, spade, Forstner, and auger bits. These parts risk overheating and melting during the drilling process.

Instead, opt for drill bits that are manufactured from hardened materials, such as diamond or cobalt. As a rule of thumb, both an all-purpose and a high-speed drill bit are valid options.

That said, we recommend using a cobalt bit that has a 135° angle for maximum accuracy, speed, and sharpness. A titanium nitride bit, although more expensive, will also do.

5. Utilize a Center Punch

Using a center punch is all about ensuring that you drill an appropriate hole into the cast iron without going off course. It’s how you make sure your drilling aim is accurate.

In other words, a center punch is quite an essential tool to have. Before you start drilling, it helps you design an indent or dimple in the place where you’re about to drill.

Fortunately, using a center punch is fairly easy, you just need to pair it with a hammer before you hit the desired drilling spot with it.

A center punch should dent the cast iron easily too since it’s harder than the metal itself. You can use a protractor and marker to make out the shape you wish to create as well.

The aforementioned steps are simply a preventative measure so you don’t end up drilling away from your aim and causing irreversible damage to the iron.

6. Use Cutting Oil or Lubricant

In our experience, wiping down your drill with cutting oil or a lubricant is an optional step. Some opt to apply the product to the cast iron instead.

Either way, since we’re drilling cast iron, this step isn’t always necessary. That’s mainly because cast iron contains a carbon percentage and that chemical acts as a natural lubricant.

So, why is this a step in our process then? Well, did you know that drilling with iron can get pretty hot due to the increased friction between the tool and the metal?

This may come across as a safety hazard. Applying cutting oil, however, can help reduce these high temperatures while you continue drilling into the cast iron.

An oil or water-based lubricant is another great option, mainly since it can reduce the risk of the metal wearing down or cracking. If you’re drilling multiple holes especially, you need to lube up too.

7. Start Drilling Safely

Start Drilling Safely

Now that you’ve set up your equipment and metal for drilling, it’s time to get down to it. Rule number one is to always start slow and gradually build up to higher speeds.

This way, if any mistakes happen, you can hastily redirect your aim. This also prevents the metal from overheating, and in turn, ensures your safety.

As you go, you’ll be increasing the size of the drill bit you’re using. We do this to quickly enlarge the hole we’re making in the cast iron.

What’s important though, is that you don’t replace the small drill bit with a bigger one until you have a clear visual of the hole’s outer shape.

You can choose to keep a consistent speed throughout the drilling process or to boost your performance slowly. Sticking to the procedures of safe drilling matters more than speed in the end.

8. Clean Up Afterward

Once you’ve finished your drilling project completely, it’s time to clean up the mess left behind. It’s not recommended to clean as you go, simply because, as you’re about to find out, the process gets too tedious.

Additionally, don’t remove your safety goggles and gloves just yet because you’ll be needing them while you clean. Metal debris is considered toxic residue and should be removed carefully.

For starters, wipe down the surface with a dry cloth and make sure that you also reach inside the drilled hole. Sweep up that waste and dispose of it separately.

Next, wet a soft fabric with some warm water and repeat the same step. Don’t attempt to reuse that wet cloth later. It’s better to throw it away for your safety.

Finally, dry the water off with another dry piece of fabric, making sure the cast iron is no longer wet so no rust forms. Remember to clean your drill bit too since the cutting oil causes debris to gather on its surface as well.


Our quick, simple guide has shown you how to drill cast iron successfully and without causing damage to the metal or harming yourself.

By following our 8-step process, you can easily drill more than one hole in such a stubborn and hard metal like cast iron. Just make sure that you follow the necessary safety procedures before you pick up your drill.

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