HOW TO DRILL CAST IRON

Cast iron is one of the most common engineering materials used in manufacturing, maintenance and repair work. It is widely used for castings, machine frames, housings, flanges, pumps, gearboxes and various structural components.

Unlike ordinary steel, cast iron behaves differently during machining. Depending on the specific grade, it can be hard, brittle and abrasive. Choosing the right drill bit and the correct drilling technique is therefore essential.

Why Drilling Cast Iron Is Different

Unlike many steels, cast iron generally does not produce long, continuous chips during drilling. Instead, it produces short chips or powder-like dust. It may also contain hard particles that accelerate cutting-edge wear.

Using an unsuitable drill bit may result in:

• rapid dulling of the cutting edges,
• poor hole guidance,
• excessive heat generation,
• reduced hole quality,
• an increased risk of tool damage.

Which Drill Bit Should You Use for Cast Iron?

For cast iron and other abrasive materials, we recommend solid carbide drill bits. Carbide offers excellent wear resistance and performs much better in materials that quickly dull conventional HSS drill bits.

For drilling cast iron, we recommend solid carbide twist drill bits according to DIN 338.

These drill bits are suitable for cast iron, cast steel, bronze, AlSi alloys, fibre-reinforced composites, thermosetting plastics and other abrasive materials.

How to Drill Cast Iron Correctly

When drilling cast iron, we recommend:

• using a sharp, rigid drill bit,
• clamping the workpiece securely,
• drilling steadily without side movement,
• using a smooth, consistent feed rate,
• avoiding excessive feed pressure,
• regularly removing chips or dust from the drilling area.

When drilling harder grades of cast iron, stable guidance of the drill bit is especially important. The more stable the drill, the lower the risk of vibration, poor hole quality or tool damage.

Is Coolant Required?

Whether coolant is required depends on the specific type of cast iron, the cutting tool and the drilling method. In practice, cast iron is often machined dry because it produces brittle chips or dust. However, it is important to monitor both tool temperature and hole quality throughout the drilling process.

When drilling in production or drilling larger diameters, always follow the recommended cutting conditions for the specific tool and material.

When to Use a Short Drill Bit or a Machine Drill Version

For precision drilling, CNC machining or applications with limited access, a short drill bit may be the better choice. A shorter drill bit is more rigid, deflects less and maintains better hole alignment.

In addition to standard DIN 338 drill bits, we can also supply short solid carbide drill bits for CNC machining as well as Morse taper drill bits for machine applications.

Summary

Cast iron is a material where choosing a highly wear-resistant drill bit pays off. Solid carbide drill bits are particularly suitable wherever conventional HSS drill bits lose their cutting edge quickly or where extended tool life is required.

If you require a different diameter, we can also supply intermediate sizes from 1.0 mm to 10.0 mm in 0.1 mm increments on request. For machine applications, Morse taper versions and short drill bits for CNC machining are also available.

Drilling cast iron is closely related to selecting the right drill bit for abrasive materials. If you also machine composites, fibreglass or carbon fibre, you may find our article How to Choose a Drill Bit for Composites useful.