Knurling Operation: Definition, Process, Types & Uses [PDF] (original) (raw)

In this article, you’ll learn What is Knurling Operation? Its Definition, Process, Knurling Tools Purpose, and Applications are all explained with pictures.

You can also download the PDF file of this article at the end.

What is a Knurling Process?

Knurling is a lathe machining process that creates a diamond-shaped pattern on a workpiece surface. It is done by using hardened metal wheels with special shapes to enhance the workpiece’s appearance and provide a better grip.

This process creates small ridges along the surface of the metal object so that it can be easily handled or lifted. These small ridges are a combination of horizontal, vertical, or crossing lines on the surface of the workpiece.

In addition, these knurled patterns improve grip, increase friction, or repair worn parts. The knurling process is usually done on a lathe machine. When a press fit is required between two parts, straight knurling is often used to increase the diameter of the workpiece.

Overview on Knurling

If you haven’t heard of knurling, you’ve probably seen a knurled product or item before. Knurled grips are often used on tools like wrenches, screwdrivers, and other hand tools. The knurling process creates a patterned texture that prevents tool slippage from the hand.

Rather than adding material to the grip, knurling creates a textured surface by cutting away some of the material or applying pressure. Tools used for knurling are designed with a specific pattern that produces the same pattern when pressed against a workpiece.

Purpose of Knurling Operation

When knurled, a product can present an attractive pattern on its surface that enhances its overall aesthetic value. However, most people will like that textured finishes are more attractive than smooth finishes.

In addition to its aesthetics, there are practical reasons for manufacturing companies to adopt knurling. It is common for hand tools, such as screwdrivers, to be knurled, which provides a better grip and makes them more usable.

For example, if the grip of the hammer is smooth, there may be a possibility of the hammer slipping from the user’s hand when striking an object. To avoid this, knurling prevents slippage of this hand by creating a textured pattern that is easy to hold.

Types of Knurling

The following are the main types of knurling operations:

Annular rings
Linear knurl
Diamond knurl
Straight knurl

#1 Annular Ring

This type of knurling is often used when the mating part is plastic. The annular rings allow for easy mating, but the ridges make it difficult to separate the components.

#2 Linear Knurl

Linear knurling is really useful to use with mating plastic pieces since linear knurling allows for greater torsion between the components.

#3 Diamond Knurl

This process is a combination of annular rings and linear knurls that create a diamond shape. It is typically used to provide a better grip on components and is the most common type used on everyday items.

#4 Straight Knurl

Straight knurling is also a type of manufacturing process. This is usually conducted on a lathe, by which a pattern of straight rolls is rolled into the material to create a textured surface.

Tools for Knurling Operation

Knurling tools are available in a variety of forms, but all serve the same function. Knuckle joint tools and revolving head tools are two common types of knurling tools. The knuckle joint tool is featured with a pair of rollers that move with the workpiece as it is being knurled.

Image: Amazon.com

The revolving head tool has three pairs of rollers to change the pitch to a different noise without changing the setup. Knurling patterns are produced in two types: diamond and straight.

Rollers come in three pitches, coarse, medium, and fine. Usually, a diamond pattern is used with a medium pitch. When working with large diameters, a coarse pitch is used; when working with small diameters, a fine pitch is used.

Hand vs. Machine Knurling

The knurling operation can be done in two different ways: by hand or by machine. The former involves using a rolling roll that produces precise patterns as it is pressed against the workpiece surface. In contrast, the latter involves using a lathe to cut the chosen pattern into the workpiece.

Hand knurling is generally the most basic method, which requires a small roller tool to operate. As the machinist moves this tool across the workpiece, it leaves a textured surface in the pattern of the tool’s indent.

Image: punchlistzero.com

On the other hand, machine knurling is a more complicated process as it requires a lathe. In contrast with hand knurling, machine knurling does not produce a textured surface through pressure. Instead, it employs a bit to cut material off from the workpiece.

Knurling Precautions

Following are some precautions considered while performing the knurling operation:

Never stop the carriage when the tool is in contact with the work and the work is still moving, as this will cause wear on the work surface.
Take a look at the knurling tool to make sure the tool isn’t forcing the work through the center hole.
During operation, keep the workpiece and knurling tool well-oiled.
Be sure not to let a brush or rag get between the rollers and the workpiece. Otherwise, the knurl will be wasted.
Be careful not to allow the knurling tool to completely pass through the end of the workpiece, or it may damage the workpiece or lathe centers.

Application of Knurling

This operation is performed to make an indentation on the surface of the workpiece. This knurled surface allows you to have a better grip on the object than a smooth metal surface. Sometimes, the knurled pattern is in a series of straight ridges instead of the more common criss-cross pattern.

Knurling can also be used as a repair method. This is because a knurled surface has expanded areas surrounding the depressed areas. These extended areas can create wear on the part. In the days when labor was inexpensive, and parts were expensive, it was possible to repair worn piston skirts by knurling them to the nominal size.

Knurling has become less popular as parts have become more affordable, and performance engine builders discourage it specifically. In addition, knurling can also be used when a component is assembled into a less precise component, such as a metal pin in plastic molding.

A knurled surface is frequently found on tool handles, mechanical pencils, pistol grips, barbell bars, motorcycle handlebars, and electronic equipment control knobs. It is also used on the grips of darts and the footpegs of BMX bikes.

Closing It Up

That’s it. Thanks for reading. I hope I have covered everything about the topic “Knurling Operation.” If I missed something, or if you have any doubts, let me know in the comments. If you liked this article, please share it with your friends.

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