What is Knurling? Explained with Examples

What is Knurling? Explained with Examples

What is Knurling? Explained with Examples

Most machined parts go through a post-processing cycle. Knurling is one such method and can be considered a post-manufacturing process.

Knurling makes a series of crests and troughs on the part.

Knurling is a machining operation that makes different patterns of straight or diagonal lines on round or cylindrical parts. It can make the patterns by removing the surface material or by displacing its position. This pattern increases the part's surface friction and provides excellent visual appeal.

This article explains knurling in detail by examining the process, applications, tools, etc.

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What is Knurling?

Knurling Guide
Some common knurl patterns

Knurling jobs are generally performed as a finishing operation on manufactured parts to imprint a specific pattern by cutting or forming the surface material.

Depending on the knurling tool used, there are various knurling patterns that can be cut on the workpiece.

Once machined, the pattern on the material surface looks like a mirror image of the pattern on the knurling tool.

Knurling imparts a better grip on tools and equipment by increasing surface friction, preventing slippage problems in hand tools and machine equipment/parts.

It is also employed as a repair method for worn-out parts. The knurling operation modifies the material surface by making concave and convex contours on its surface.

These newly formed countors compensate for the worn-out material surface.

Hand Knurling vs Machine Knurling

Hand knurling vs machine knurling
Hand knurling vs machine knurling

Knurling operation can be performed on a material surface manually using hand tools or by machines.

Hand Knurling

Hand knurling jobs are done using a hand-held knurling tool called a hand knurler. It can have one or more knurl wheels depending on its holding setup.

A knurling wheel is a small roller tool having patterns like diamonds or diagonals indented onto its face.

When the hand knurler is tightened to the material surface and turned, it deforms and modifies the material's surface as the knurling wheels press against it.

Hand-knurling is a feasible way, but it has inherent inaccuracies. The hand knurling process must be continuous without pause to prevent the overlapping of knurl lines.

Machine knurling

Machine knurling operations are performed on a machine, usually on a manual or CNC lathe. This knurling operation is continuous and usually error-free. 

The knurling wheels are secured on a knurl holder attached to the worktable. Then the knurl clamps the workpiece with a firm grip.

Knurl wheels clamped to a workpiece
Knurl wheels clamped to a workpiece

For the knurling job, the tool or cutter is positioned perpendicular to the part.

Before turning, the stock is lubricated to prevent overheating and ease cutting by smoothly interfacing the stock and tool.

The chips are cleaned continuously to prevent pile-up that can cause interruptions to the machine resulting in job failure.

In machine knurling, you can use a double-wheel knurling tool to make complex geometric patterns.

Good quality knurl patterns with a certain level of complexity can only be achieved when knurled with a machine.

The Knurling Process-How it's Done

The knurling process involves using knurling wheels with V-shaped tooths to produce bumps or depressions on the surface of a workpiece.

It makes straight or angled line patterns on the workpiece. Knurling works best on a cylindrical or round stock.

After clamping the workpiece and tool, the knurling operation starts with user-specified machine parameters such as the speed (RPM) and feed.

During the process, adequate support is provided to the workpiece to avoid deformation. It is essential to machine a precise part.

However, the blank diameter must also match the knurling tool's pitch to properly mesh the two surfaces to prevent jagged burs caused by wheel overlapping.

Further, you can use a good quality coolant, lubricant, and double-wheel knurling tool to produce complex patterns.

You can reduce the processing time and make high-precision repeatable parts by using a programable machine like a CNC lathe.

Operating a CNC lathe machine is relatively easy compared to conventional turning machines.

Knurling tools- 3 Types

Knurling tool
Knurling tool

Knurling tools have a series of uniform V-shaped tooth patterns on their surfaces. These teeth get indented on a part surface when pressed against them.

There are three common knurling tools, each used for specific jobs.

Internal Knurling Tool

Internal knurling tools are primarily used with hand knurlers. They are favorable in making knurling patterns of specified depth.

Convex Knurling Tool

Convex knurling tools are prescribed as axial feed tools. They have sharp leading edges spreading out the loading areas.

Conical/Concave Knurling Tool

Conical knurls, also known as concave knurls, provide a smooth and precise finish while simultaneously generating radial face or conical surfaced knurling.

These conical surfaces imprint a decorative finish on the workpiece.

Applications of Knurling

Some knurled parts
Some knurled parts

The functional and decorative characteristics of knurled parts have many applications.

Some of the most common applications include structural parts, utensils, furniture, architectural components, and machine components like piston cylinders.

Grip Enhancement 

Knurling is desirable in many operational parts and equipment used in the industry and the household.

The process increases the performance and usefulness of the part surface essential for gripping.

A firm grip avoids the problem associated with slippage in applications such as tool handles, pistol and hammer grips, or the gripping surfaces of motorbikes.

Knurled nuts are used in medical equipment, assembled sheets, musical instruments, appliances, etc.

These nuts can be tightened and made loose without the help of a tool.

Part Repair

Due to the increased cost of replacing machine parts, the knurling process is used as a repair mechanism to compensate for worn-off material.

Low Precision Assembly

Parts that do not require exact assemblies, such as the assemblage of plastic with a metal or composite, can utilize a knurled surface.

For example, you can assemble a metal pin in plastic molding.


Knurling operations are also used to provide curved line patterns on parts.

Such unique designs improve the attractiveness of a product and increase its demand.

Frequently Asked Questions (FAQ)

What is knurled welding?

In knurled welding, the pattern is engraved on both sides of the tool's surface. Later this tool is used to RF-weld the fabrics together.

What is the most common use of knurling?

The most common use of knurling is to engrave grip patterns on handles and equipment surfaces. The patterns can be crisscross, straight, or helix ridges.

What are knurling characteristics?

Some desirable characteristics of knurling include stable part geometry, corrosion resistance, and attractive design.

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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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