How to Drill Cast Iron | Perfect Ways

Drilling holes in cast iron without breaking or creaking the material is a demanding task. But learning how to drill cast iron properly can make the task pretty straightforward. Creating a hole in cast iron requires more skill than using the right drill bit.

Luckily, we have covered an effective method of drilling through cast iron that will help you create precise drilling without breaking the material. The technique includes safety prosecution, using the right kits, and proper methods to extend the possibility of success over cast iron. But let’s have a look at what makes drilling through cast iron a challenging task.

Challenges of Drilling through Cast Iron

The composition of cast iron makes it a bit tough to use or repair. Though many people believe cast iron is pure iron, it’s not true. It is needed to melt down pig iron, iron ore, scrap metals, and other alloys, pour into molds, and finally solidify to create cast iron.

Due to the presence of different materials, cast iron carries various properties, which make it more prone to fractures and cracks. Thus, without handling properly, you can easily break this brittle material.

How to Drill through Cast Iron

The cast iron drilling process is pretty straightforward; however, there is a risk of breaking down. Since it’s a soft metal, follow these steps carefully to successfully drill through it:

Tools needed:

Apply the right speed

The top drill through cast iron doesn’t apply any faster speed than 150 SFM (surface feet per minute). This value is also related to the power drill’s RPM (revolutions per minute):

RPM = SFM x 3.83/ drill bit diameter

It’s meant for a ½ diameter hole, you can apply a maximum 1146 RPM drill speed, which is mid-range for most of the corded and cordless drills. You can use this speed to cut up to half the cast iron in the winter. Since the cold temperature influences the fragility of metal, it’s better to lower the speed to 300 RPM.

Mark the drilling point

Identify the work spot on the cast iron where you want to drill a hole.  Making the spot clear will help place the drill bit in the exact place and prevent drilling into the opposite side of the existing half of the hole. So, use a marker or marker and leave a cross sign or circle on the surface of the cart iron.

Another important thing is that drilling a pilot hole on a brittle metal will help it successfully drill through its large hole. Use a smaller drill bit to create a starter hole on the cast iron. It will also let you do some practice before creating a larger hole.

Check the drill bit

Double-check the drill bit to see if you have picked the desired size or not.  Apart from this, compare the bit size with the marked area to be sure about the size. Even you can practice on a useless piece to find out what size of hole you are going to drill. You should also check the sharpness of the bit and use the best drill bit for cast iron that has a 135-degree point angle.

After that, secure the cast iron if it is a loose piece. If it is already connected with something, still have to brace the cast iron in some cases. The intention is to prevent both the working surface and the cast iron from moving during drilling through it.

Start drilling

After stabilizing the workpiece and marking the point, you can now carefully start drilling. Firstly, hold the trigger strongly and push the bit gently against the cast iron. It will deburr the hole and, during this time, slough off the metal shavings around the hole.

After drilling a hole, wipe down the surface with a dry cloth and then a wet one. After drying off completely, check the hole carefully. If you find anything rough inside the hole, you can still apply a couple of passes to make it smooth.

Carefully complete every drill pass so it doesn’t snag or be prone to sticking. Feeling so is a sign of damaging the cast iron and leading to the creaking or breaking.

Is it better to use lubrication?

Cast iron is rich in carbon content, which naturally acts as a lubricant. It means you don’t need to frequently apply the lubricant to reduce the temperature while drilling through cast iron. It’s a huge advantage of working on cast iron as lubricants are messy. So applying lubricant can make it difficult to control the bit while working, especially for beginners.

Still, if you want to use lubricant, choose between an oil-based or water-based lubricant to lower the risk of wear and tear and the cracking of the drill bit. Conversely, many professional enthusiasts recommend using lubricant for drilling plenty of holes on cast iron. It helps prevent heat build-up in the bit and allows drilling holes in cart iron successfully.

Safety tips to remember while drilling through cast iron

Safety is vital and a must for convenient drilling tasks. So, maintain this safety measure to prevent injury and damage to the project, especially when handling cast iron:

Use extra cutting fluid during consistent drilling

Using a drill bit consistently for a longer time will build up its temperature. So, take an interval, remove the debris and apply cutting fluid for a safer and better experience on a longer drilling project.

Start with slower speed

Higher speeds usually cause more friction, which builds up the heat. Conversely, a slower speed will let you drill through cast iron without overheating the power drill and making the drill bit dull. So don’t run over 3000 RPM while less than 1000 RPM is more preferable.

A step bit is ideal for a large hole

If you need to drill a larger hole through cast iron, it will be better to use a step bit. But make sure you are drilling at a slower speed at the step bit will create too large a hole if you drill at a higher speed.

Always keep an old rag

Whether it is cast iron or another metal, you should always keep an old rag close while using a drill bit. You will find it healthy to remove extra cutting fluid and metal particles. Even it will prevent accidental injury that may result from inadvertently wiping the bit on your pants or shirt.

Mark the drill point

Identifying the drilling spot will give a clear idea of where you need to place the bit. Drilling through guesswork won’t offer a precise finish, especially if you need to maintain a distance between holes.

Check the wide of the material

If you need to drill at the desired depth, check the width of the working surface and fix the depth so you don’t go too far. To handle the issue properly, you can always keep a leveller and a ruler in your toolbox.

Don’t drill into loose cast iron piece

The movement of cast iron while drilling through it can creak the hole and the entire piece as it’s a brittle material. Thus, secure the piece for stable work.

FAQs on How to Drill Cast Iron

What is the best drill bit for cast iron?

A cobalt drill bit with a 135-degree point angle is the best drill bit for cast iron. Its angle is sharper than a typical drill bit, which makes the drilling task precise and accurate. To make the purchase worthwhile, you can pick up this Hymnorq Metric M35 Cobalt Twist Drill Bit Set. 

Is it possible to tap cast iron?

The rare hard spots in the cast iron can creak the drill bit tip, especially when applying extreme pressure to it. Therefore, it requires extra care to prevent breaking taps while encountering hard posts.

Can I cut cast iron pipe?

Sometimes it is necessary to replace the old cast iron pipe, especially if the pipe has become considerably weakened. So you can buy a replacement cast iron pipe and replace it with the older one by cutting it down to size. You can cut cast iron pipe using an angle grinder pretty easily.

Final words

Once you have learned how to drill cast iron, it won’t be a challenging task for you. Just bring those suitable kits and follow the process we have discussed. Even you will find these drill bits and techniques handy for a wide range of drilling projects.

Despite don’t forget those safety tips. They are vital for a precise and successful drilling season, especially for brittle materials like cast iron. Finally, invest in the best drill bit and power drill as well as make the hand dependable to conquer any drilling task.

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Sam Morgan is a general contractor based in Charlotte, North Carolina. He does home renovations, extensions, landscaping maintenance, and general handyman jobs for homeowners. He is also the part-time content writer at Machine Handyman and a lifelong tools enthusiast. Sam loves hand tools, power tools, machinery, and DIY gadgets of all shapes and sizes! He is always researching the different types of home improvement tools that will get the best results. This site will cover products like power drills, air compressors, saws, nail guns, screw guns, grinders, cutting tools, and many more.

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