Can Cast Iron Be Drilled?

In this article, I’ll show you how to drill a cast iron surface easily.

As a handyman and engineer, I have frequently drilled into cast iron. Cutting neat holes in cast iron can be easy. With the right drill bit, technical know-how, and other suitable materials, you can drill a neat hole in your cast iron surface without a hitch.

In general, to drill holes in cast iron:

  • Clean the Area
  • Choose a Drill Bit for Cast Iron
  • Use a Proper Drill
  • Make a Center Punch on the Cast Iron
  • Drill the Cast Iron Using Cutting Oil

I will cover more detail below.

How to Drill into Cast Iron

Whether or Not to Lubricate

Although many machinists advise against lubricating when drilling through cast iron, they are divided on the subject.

Because carbon acts as a lubricant in cast iron, it is often acceptable to drill iron without lubricant. Lubricant is a slick substance that can prevent metal debris from falling away from the bit as you drill.

A lubricant, such as oil or a water-based coolant, cools the drill bit and the metal, preventing cracking or excessive bit wear.

Bottomline. If you’re only drilling one or two holes, the object will lubricate your bit; however, if you’re drilling a lot of holes, your bit will probably last longer if you apply a few drops of cutting oil or spray lubricant before each one.

Drill Bits

You don’t have to look far for a bit to drill through cast iron, but not every bit is suitable.

What to Avoid

Cast iron should be drilled with drill bits intended for wood and masonry. Cast iron would destroy the extra-wide flutes of a wood boring bit, and a masonry bit is designed to be used with a hammer drill; the dull tip of a masonry bit would take all day to penetrate cast iron. Forstner, spade, and auger bits are incompatible with cast iron.

What to Use

Cobalt drill bits with a 135-degree point angle are ideal for cast iron.

The angle is sharper than on a standard bit, allowing faster and more accurate drilling. Cobalt bits have a brassy appearance. You can also use a gold-colored titanium nitride bit as an alternative. Any high-speed steel bit designed for metal, including all-purpose bits, is appropriate for cast iron. A bit with a 118-degree point angle could drill smoothly and produce fewer shards when using a drill press.

Tapping — any metal tap will work on cast iron, but you may prefer to select one designed specifically for cast iron.

Drilling Speed

The peak drilling speed recommended for soft cast iron is 150 surface feet per minute (SFM). The following formula relates this value to drill revolutions per minute (RPM):

SFM x 3.82/drill bit diameter = RPM

The maximum drill speed for a 1/2″ hole should be 1,146 rpm.

How to Drill Through Cast Iron

Step 1: Clean the Area and Determine the Properties

Before beginning the drilling, thoroughly cleanse the area and understand cast iron’s properties. Water can cause rusting in cast iron. So, when cleaning, if there is any rust, remove it.

Cast iron material is typically a mixed metal. Iron is blended with 2-4% carbon, varying amounts of silicon and manganese, and contaminants like sulfur and phosphorus. Cast iron is hardened as a result of this combination.

Step 2: Choose a Drill Bit for Cast Iron

When choosing a drill bit, keep the hardness of the cast iron in mind.

Cobalt has a Rockwell C hardness of 65.5 to 67.  I strongly suggest using a cobalt drill bit for the cast iron drilling.

Step 3: Use a Proper Drill

When choosing a drilling machine, consider your comfort level. Due to the hardness of the material, you must apply constant thrust to the drill while drilling. 

Bench drilling can provide constant force by hand and can be used to perform a safe and accurate drilling process.

Because of the high hardness of cast iron metal, hand drilling is not recommended.

Step 4: Make a Center Punch on Cast Iron

Before you begin drilling, make the center punch to prevent the drillbit from moving around. It is critical for tool safety, accuracy, and tool life.

The drilling point can be centered. If you have a larger diameter hole, you can drill it using a tiny drill bit.

Step 5:  Drill Cast Iron with Cutting Oil

Drilling is done in opposition to friction. Both the tool and the material are heated as a result of friction. When the melting point of the tool is lower than the generated temperature, it will be heated.

The melting point of cast iron is 1127-1204 C. (Cutting oil can be used to lower the temperature.)

The tool and workpiece become extremely hot when you drill at high speeds. So, when drilling, use the slowest speed possible because chips are easily removed.

Step 6: Begin the Drilling Process

You should start slowly and gradually start increasing speed for the best and most efficient drilling process. You won’t be able to drill the metal properly if you don’t have a pilot hole or a punching point. Because of the hard surface, the drill bit will move here and there. 

Take a look at some of our related articles below.

Video References


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About Sam Orlovsky

b1d87d2ee85af3e51479df87928bdc88?s=90&d=mm&r=gCertifications: B.E.E.
Education: University Of Denver - Electric Engineering
Lives In: Denver Colorado

Electrical engineering is my passion, and I’ve been in the industry for over 20 years. This gives me a unique ability to give you expert home improvement and DIY recommendations. I’m not only an electrician, but I also like machinery and anything to do with carpentry. One of my career paths started as a general handyman, so I also have a lot of experience with home improvement I love to share.

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