Can You Tap Cast Iron

Tapping cast iron can be a tricky process, but it is an essential skill for any machinist or DIY enthusiast. Cast iron is a popular material for machine tables, jigs, and fixtures, but it can be difficult to work with due to its hardness and brittleness. In this article, we will discuss the process of tapping cast iron, including the tools and techniques needed for success.

Understanding Cast Iron

Before we can discuss tapping cast iron, it’s important to understand the properties of this material. Cast iron is a hard and brittle alloy made primarily of iron, carbon, and silicon. It is commonly used in industrial applications due to its high compressive strength, good wear resistance, and low cost.

Selecting the Right Tools

To tap cast iron, you will need a few specialized tools, including a drill, tap, and die set, and some cutting oil. When selecting your tools, it’s important to choose ones that are designed for use with cast iron. Look for high-speed steel drills and taps with a high cobalt content, as these materials are better able to withstand the hardness of cast iron. A good cutting oil will also help to reduce heat and friction during the tapping process.

Preparing the Workpiece

Once you have your tools, it’s time to prepare the workpiece for tapping. Begin by marking the location where you want to tap the cast iron, and use a center punch to create a small indentation. This will help to guide your drill bit and ensure that the tap hole is straight and centered.

Drilling the Hole

Next, use your drill to create a pilot hole in the cast iron. Be sure to use a slow speed and plenty of cutting oil to prevent overheating and reduce the risk of breaking the drill bit. As mentioned in, you can use a drill and tap chart to determine the ideal drill bit size for your tap.

Tapping the Hole

Once you have drilled the pilot hole, it’s time to tap the cast iron. Begin by applying cutting oil to the tap and workpiece, and then insert the tap into the hole. Use a back-and-forth motion to slowly cut threads into the cast iron, making sure to keep the tap straight and perpendicular to the workpiece. As mentioned in, this back-and-forth motion is critical for preventing the tap from breaking and ensuring that the threads are straight and even.

Finishing Up

After you have tapped the hole, it’s important to clean up any excess material and debris. Use a tap wrench to remove the tap from the hole, and then use a die set to clean up the threads. Be sure to apply cutting oil during this process to reduce friction and prevent damage to the threads.


Tapping cast iron may seem like a daunting task, but with the right tools and techniques, anyone can do it. Remember to choose high-quality tools designed for use with cast iron, and take your time to carefully drill and tap the hole. With practice and patience, you’ll soon be able to tap cast iron with confidence.


Can I tap cast iron?

Yes, you can tap cast iron as long as it is not too thick. You should use a special tap specifically designed for cast iron and use slow, steady pressure to ensure the tap remains sharp while drilling.

What type of drill bit do I need to tap cast iron?

You should use a special tap specifically designed for cast iron. Some recommended taps include spiral point taps, hand taps, and spiral flute taps.

What speed should I use when tapping cast iron?

When tapping cast iron, you should use a slow and steady speed. This will ensure the tap remains sharp and will prevent it from breaking.

Are there any safety precautions I should take when tapping cast iron?

Yes, you should always wear safety glasses and gloves when tapping cast iron. You should also make sure the area you are working in is well-ventilated to prevent exposure to toxic fumes.

Is it difficult to tap cast iron?

Tapping cast iron is not difficult if you use the correct tools and techniques. However, it is important to use slow and steady pressure to ensure the tap remains sharp while drilling

James P Alameda
Latest posts by James P Alameda (see all)

Similar Posts

Leave a Reply

Your email address will not be published. Required fields are marked *