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 Knurling?
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.
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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 creates 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.
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Before the knurling operation, the machinist should determine the location and length of the knob and then set the machine to Knurl. With a medium feed, it is necessary to keep the speed slow. Speed is usually set at 60 to 80 rpm, while the feed is best for spindle revolutions from 0.04 mm to 0.08 mm.
When setting the knurling tool in the tool post, ensure that the axis of the knurling head is at center height and that the face of the knurls is parallel to the workpiece. Before turning ON the machine, check the rollers that move freely and are in good cutting condition.
When performing knurling operations, it is necessary to oil the knurling tool cutting wheels where they contact the workpiece. Bring the cutting wheels or rollers up to the surface of the work so that about 1/2 of their face is in contact with it.
It will be easier to start the knurl if the roller face is placed in an above-mentioned manner, and it will cut smoother too. The area to be knurled should be generously coated with oil. Now, start the lathe, forcing the knurl into the workpiece about 0.05mm.
As the knurl pattern begins to form, engage the carriage feed lever. Once the knurl has been turned a few times, shut off the machine and observe it. Make sure the knurl is tracking properly and is not double-tracked.
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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 creates 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 in order to create a textured surface.
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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.
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 perform the operation. As the machinist moves this tool across the workpiece, it leaves a textured surface in the pattern of the tool’s indent.
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.
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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.
Read Also: What are Different Shaper Machine Operations?
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 on 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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