Boring vs Reaming: Differences Explained

Boring vs Reaming: Differences Explained

Boring vs Reaming: Differences Explained

Boring and reaming are two commonly used operations to make holes in workpieces.

Both operations are performed on already drilled holes to get the desired dimension, accuracy, and surface finish.

So, what exactly is the difference between boring and reaming?

The difference between boring and reaming is that boring enlarges an existing hole, increasing its diameter by removing material, while reaming finishes the hole surface by removing any irregularities present on the hole surface, improving its tolerances and dimensional accuracy.

This article discusses the differences between boring and reaming operations while providing an in-depth guide to both operations.

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Difference Between Boring and Reaming

Material Removal Rate (MRR)The material removal rate is relatively higherMinimal material removal rate
Order of ExecutionPerformed after a hole has been machined by a drillPerformed as the last step for finishing the hole surface
Cutting ToolBoring bar which is a single-point cutting toolReamer which is a multi-point cutting tool
Length of cutting edgesShorter cutting edgeLonger cutting edge
SpeedRotational speed is lowRotational speed is relatively higher
Machining timeSlowerFaster
MachinesLathe and milling machines can perform boringUsually drill presses and lathes can perform reaming
TypesLine boring, Back boring, etc.Straight reamer, Shell reamer, Rose reamer, etc.
Surface finishSurface quality is comparatively roughSmooth surface finish is attained
Difference between boring and reaming

Differences Based on the Process 

Both boring and reaming follow the principles of metal cutting operations but differ in terms of the resulting hole surface, material removal rate, and sequence of operations.

Boring removes a significant amount of material from a hole's inner surface to enlarge it, thus increasing its diameter and resulting in a higher material removal rate.

Performing a boring operation on a CNC lathe (Source: Inlet Tool Inc.)

Contrarily, reaming finishes a hole's inner surface, removing any burrs or smoothing any uneven surfaces, which removes a negligible amount of material. 

The resulting hole diameter has a very slight increase in its diameter, and the material removal rate is very low.

Moreover, boring is done after a drill press has already machined a hole in a workpiece. Reaming is performed after boring and any other machining operation for finishing the hole's inner surface.

Differences Based on the Cutting Tool

Boring bar and reamer
Boring bar and reamer

The boring bar has a single cutting point, and the optimal RPM for boring is relatively lower than reaming, leading to a longer machining time.

The boring bars have a single cutting edge that is usually shorter than the multiple cutting edges on reamers.

On the other hand, reaming involves a multi-point cutting tool with high spindle speed, thereby increasing the material removal rate and reducing the processing time.

Depending on your requirement, there are different types of reamers available and you have to select the right tool for your application.

Differences Based on the Machinery 

Machines used for Boring and reaming
Machines used for Boring and reaming

Boring operations can be performed on a CNC lathe, conventional lathe, or milling machine. However, the boring tool used on a milling machine is different from the tool used on lathes.

On the other hand, reaming can be performed on a drill press or a lathe machine.

Unlike boring, the same cutting tool can be used for reaming on both machines.

Apart from that, boring has different categories like line boring, back boring, etc., with the boring bar being supported at both ends in line boring and clamped at only one end in back boring.

Reaming also has various types like rose reaming, shell reaming, straight reaming, etc., each differing based on hole diameter and contour.

Differences Based on Quality 

The final surface quality in boring is slightly rough, whereas reaming achieves a smooth inner hole surface.

In boring, an increase in the depth of cut and feed rate increases surface roughness and decreases surface quality.

On the contrary, reaming involves a shallow depth of cut, and an increase in feed does not have any significant effect on the surface quality.

What is Boring?

Boring operation
Boring operation

Boring is a hole-enlarging machining operation that utilizes a single-point cutting tool, known as a boring bar.

Depending upon the application and the cutting force to be delivered, boring bars can be made of steel, carbide, or heavy metal.

The use of a single-point cutting tool reduces the material removal rate, leading to a long machining time, and rough surface finish, with high accuracy.

Applications of Boring

Boring a large hole in a workpiece
Boring a large hole in a workpiece

A large-scale application includes boring smooth tunnel holes in hard rock or sand.

Boring is also performed on couplings and engine cylinders of automobiles.

Small-scale applications also include boring steel or aluminum hollow shafts and rods. 

Advantages of Boring

The boring process provides the ability to enlarge holes with a high length-to-diameter ratio.

This operation is simple, straightforward, and efficient in obtaining the desired result.

The machines used for boring operations are durable and have a long life.

Boring an already drilled hole improves its surface quality and tolerances.

What is Reaming?


Reaming is a hole-finishing and refining operation that utilizes a multi-point cutting tool, known as a reamer.

Different materials require different cutting forces for material removal, and generally, high-speed steel (HSS), high-carbon steel (HCS), and carbide reamers are used for reaming operations.

The machining time is relatively lesser, and the resulting surface is highly accurate and smooth.

Applications of Reaming

Piston head with reamed hole for Gudgeon Pin
Piston head with reamed hole for Gudgeon Pin

Reaming has significant scope in metalworking operations.

It is commonly used for refining the inner surface of parts such as nuts, automobile engine cylinders, hollow shafts, etc.

You can also perform reaming for smoothening the inner surface of a gear or a door lock slot.

Advantages of Reaming

Reaming is faster and cheaper than boring due to cheaper tooling and equipment.

It is a simple and quiet operation with a low material removal rate, making it ideal for materials that are difficult to machine and require longer cycle times.

Reaming tools and machines are also very durable and possess a long life.

Final Thoughts

Both boring and reaming operations are crucial machining operations that are performed at different stages in a series of machining operations.

For instance, after drilling a hole in a gear stock, boring can be performed to enlarge the hole as per requirement, and lastly, reaming can finish the hole’s surface, making it smooth and accurate. 

The reamer or boring bar should preferably have a smaller length to avoid unwanted vibration that may damage the tool and machine.

Whenever you need to machine a hole, drilling followed by boring and reaming is the way to go.

Frequently Asked Questions (FAQ)

What is drilling?

Drilling is the process of using a multi-point cutting tool to remove the material from a workpiece and produce a hole of the desired diameter. Unlike boring, the size of the drilled hole is equal to the diameter of the drill bit used for the operation.

Can reaming produce threaded holes?

No, reaming cannot produce a threaded hole. It can only be used to enlarge and finish an already drilled or bored hole.

What safety precautions should be taken while performing boring or reaming?

The safety precautions that should be followed while performing boring and reaming includes wearing a face shield, headgear, safety boots, gloves, and a protective coat. A machine guard should ideally be installed to prevent chips from flying around and causing potential injury.

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Hey I'm John. I write about Manufacturing, Metalworking, CNCs and Lasers at Mellowpine. If you have any questions related to CNCs or Lasers, I'd be happy to answer them. Reach me at mail@mellowpine.com

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Hey I'm John. I write about Manufacturing, Metalworking, CNCs and Lasers at Mellowpine. If you have any questions related to CNCs or Lasers, I'd be happy to answer them. Reach me at mail@mellowpine.com

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