Knurling: Techniques, Tools, Patterns, Process, Advantages

Knurling is a machining procedure that includes cutting small ring patterns onto the surface of a material to improve friction and visual appeal. Companies use a variety of post-finishing methods to give machined items unique characteristics.

Knurling is one of the ensuing processes. It can enhance the appearance of customized items by creating unique patterns such as ridges and swirls on milled surfaces. appeal, endurance, and traction than the initial smooth metal surface. A knurled pattern is frequently used on plastic mold casting to produce the impression of knurling in molded items. Tool handles, mechanical pencils, pistol grips, barbell bars, motorcycle handlebar grip surfaces, and control knobs on electronic devices are just a few examples of objects that commonly feature knurling.

What is Knurling?

Knurling is a manufacturing process that uses a machine called a lathe to roll a design of angled, crossed, or straight lines onto the surface of an object. The knurled section has greater aesthetic appeal, endurance, and traction than the initial smooth metal surface. The knurled pattern is frequently used on plastic mold casting to produce the impression of knurling in molded items.

Various forms of knurling vary depending based the purpose and extent of the job. We’ll talk about several knurling styles, knurling techniques, and the benefits and downsides of all of them in the following part.

Materials That Can be Knurled

There are different types of materials where the knurling process can be performed. Let’s take a brief look at some of the materials.

• Metals: Some of the most common materials used for knurling are metals. Mild steel, aluminum, brass, and stainless steel, among others, are some of the most prevalent metals used in knurling. Harder metals are more difficult to imprint and are therefore typically machine-knurled.
• Plastics: Some types of plastic also can get knurling depending on its strength. Knurling plastics require a more cautious approach due to the material’s lower heat resistance and susceptibility to failure.
• Woods: It may sound surprising but it is possible to knurl wood however it is not as simple as metal or plastic. Knurling works best on hardwoods and is limited to simple patterns, with checkering being the most popular.

Types of Knurling Techniques

There are multiple types of knurling methods, and each has special qualities and uses. The material, intended texture, and particular needs of the workpiece all influence the knurling procedure that is selected. The following are a few typical knurling procedures:

Manual Knurling

• Using ordinary household instruments (like pin drills) or special hand equipment (like a knurling tool) to get a desired pattern is called manual knurling.
• This knurling process works well for customized components or small-scale manufacturing.
• It can be used on a variety of goods, such as pens, screw heads, footpads, pistons, turntable control knobs, and irregular forms.
• Hand-knurling may be performed with a custom-engraving tool to create distinctive and craftsman-made items.
• This was the standard technique for handcrafted tools and instruments before the introduction of precision machine tools, and it is still employed decoratively in extremely high-value applications and one-of-a-kind pieces.

Mechanical Knurling

• Mechanical knurling is accomplished utilizing an especially designed knurling machine and works best in medium-volume productions where uniformity is important
• Knurling is typically done on flat surfaces using a milling machine and on cylindrical objects with a lathe.
• This is typically done on part of a plastic molding tool to produce a knurled pattern in the molded pieces

Types of Knurling Tools

Some knurling tool variants are used, depending on the final product and its applicability. For the best knurling, take into variables like material, ductility, and hardness. Let’s take a quick look at the essential equipment needed for knurling.

Knurling Wheels

• These are the most popular tools used for knurling metals.
• It typically has multiple strengthened steel discs with alternating slanted knurl patterns.
• To achieve the desired knurl pattern, such wheels are usually attached to knurling tools and driven onto a rotating workpiece.

Knurling Dies

• High-speed stainless steel is used to make knurling dies, which form patterns that cut an object’s internal surface.
• Turret lathes and CNC turning services utilize such dies as a tools for creating knurled patterns on cylindrical objects.
• Place these knurling dies in the tool holder and rotate them against a workpiece to create the desired knurled designs.

Floating Knurling Tools

• You may be required to create knurling designs and grooves on an uneven or curved surface. In such cases, you may find the floating knurling tool comes in handy.
• The floating tools feature articulating arms or spring-operated systems that maintain the knurling wheels aligned with the surface traits.
• By adapting to the the curve of the workpiece, these tools provide a precise and uniform knurled finish.

Knurling Inserts

• Knurling inserts are specific instruments that can be mounted on a lathe and used for machining.
• A specific knurl pattern is embedded into knurling inserts to create the desired knurled finish.
• Usually composed of carbides or high-performance steel, the inserts are available in a range of shapes and sizes.

Push-Type Knurling Tools

• Push-type tools often feature a knurling wheel attached to a handle, which allows the wheel to roll over the surface of the object to generate the desired knurling texture.
• These tools are hand-held equipment that create knurled patterns by applying manual force. They work well with manual or small production operation.

Types of Knurling Patterns

Although knurling enhances the grip and appearance of a part, various knurl designs have distinct applications and functions. Different sorts of knurling patterns are created depending on the intended application. Some of the various knurling patterns are briefly explored in this section.

Straight or Standard Knurling Pattern

• Straight knurling creates vertical-line and channel designs on the exterior of a workpiece.
• This method often involves drawing bordering lines, either parallel or diagonal, using a specially designed knurling tool with two hardened wheels with diagonal teeth.
• This approach works best with cylindrical things such as handles and knobs.
• Lots of companies use straight knurling on their products to provide a regular pattern that helps to grip as well as handling.
• It works well for uses such as premium products pencils, custom hardware, and jewelry, giving it a fashionable appearance.

Diamond Knurling Pattern

• A common technique called “diamond knurling” leaves tiny ridges or indentation patterns on the workpiece’s surface that mimic tiny diamonds.
• It entails the addition of diagonal lines that cross one another to create several structures in the form of diamonds.
• It is a kind of knurl that works well in handles, knobs, and machine parts since it doesn’t slip.
• Given its strength and longevity, it’s an excellent option for settings where the grip has to endure repeated, continuous use.
• The sharp edges and pattern of diamond knurls provide them optimum grip. It is the kind most frequently encountered on everyday products.

Right-Sided Knurling Pattern

• One of the most popular patterns featuring diagonal lines which descend from the top left to the lower right when observed from the bottom of the cylindrical object is right-handed knurling.
• It creates diagonal knurls that slope to the right, and since it offers a nice grip, it is frequently utilized in many different industries.
• Because of its adaptability, a right-handed knurling pattern can be applied to a wide range of objects, including knobs, handles, tools, machine parts, jewelry, barbell bars, consumer electronics, and even optical instruments.
• As over 90% of people are right-handed, this pattern is among the most common because it accommodates the right-hand grip.

Left-Sided Knurling Pattern

• In contrast to the more popular right-handed knurling, left-handed knurling is much less common and is typically done primarily for decorative purposes.
• This style was employed by several producers for specific products, such left-handed tools.
• They have diagonal ridges that rise from the uppermost right to the lower left when viewed from the end of the cylindrical item.
• It should be noted that applying left-handed and right-handed knurls together in a two-wheel holder can produce diamond patterns.

Helical Groove Knurling Pattern

• Making diagonal lines in the shape of a swirl or spirals on a surface of an item is known as the helical knurling technique.
• With cylindrical components such as handles, knobs, and shafts, helical knurling improves their functioning.
• A strong grip is made possible when rotating and manipulating the machined item thanks to the helical knurled finish.
• Companies commonly utilize this knurling patterning on cylindrical surfaces, comparable to screw threads.

Grades of Knurling

Grades of knurling is determined by the depth of the ridges it creates on the product. The knurling grades can be divided into three major grades which are explained briefly here:

Fine Grade Knurling

• This grade of knurling can be recognized by its precise diamond pattern.
• Fine grade knurling is commonly employed in optical instruments, jewelry, and gadgets because it provides a strong grip without causing damage to the body.
• It might not be useful in jobs where strong grips are preferred.

Coarse Knurling

• A design that offers a firm grip even when wearing gloves or coming into contact with greased hands or objects is indication of coarse knurling.
• Its aggressive design is commonly seen in tool handles and machinery, as well as practically all applications requiring a firm grip.

Medium Grade Knurling

• This is typically in between grade of knurling.
• This is not a widely recognized grade; rather, it frequently refers to a grade that falls between fine and coarse knurl grades.

Process of Knurling

Knurling is a lathe machining operation that can use either a subtractive process or cold-working methods. The knurling method uses knurling wheels to create the intended designs on the surface of the product. We will take a brief look of knurling process in this section.

Selecting the Suitable Metal for Workpiece

• Initially selecting the suitable type of metal as workpiece for the knurling is most important part.
• The material used must be pliable enough to stretch under the pressure exerted by knurling wheels or tools.
• More rigid substances may necessitate specific knurling wheels and reduced speed.
• The frequently used metals for knurling include aluminum, special polymers, brass, and steel.

Selecting the Appropriate Knurling Technique

• There are two different methods of knurling: manual knurling and mechanical knurling.
• In manual knurling, a small rolling tool is pressed onto the workpiece’s surface to produce the design you want. This approach is useful for softer metals.
• In contrast, the mechanical method involves cutting a design that is required into the workpiece with a lathe. This can be used for best outcome in hard metals.

Preparing the Knurling Wheel

• Depending on the type of use, knurling wheels are designed with multiple tooth sizes, materials and angles.
• You can pick the tooth types depending on the pattern and the roughness of knurl you want to achieve.
• Knurling equipment should be mounted onto a knurl holders and fastened to the worktable.
• These knurling tools have the reversed pattern of the knurl that you want for your metal.

Applying the Lubrication

• Applying the lubrication is another important step during knurling process.
• Make sure that the knurling equipment and workpiece gets enough cutting oil or lubrication during the entire process.
• Lubricants helps to reduce the friction that can generate the unwanted heat and wear the tools.
• It also ensure the smooth and knurled finish product.

Mounting the Workpiece

• You need to insert the workpiece onto a lathe chuck in the subsequent step.
• It’s critical to use grips to secure the workpiece’s stability to prevent accidental shifting during the knurling operation.

Feeding the Wheel into the Workpiece

• As the workpiece starts to rotate, gradually introduce the knurling wheels.
• The key to getting even knurling is to align perpendicularly and apply constant pressure.

Producing the Desired Pattern

• The wheel must be continuously fed into the workpiece while the necessary pressure is maintained to create the bumps or cuts on the workpiece’s surface.
• Achieving sharp and high knurls in a comparatively tougher material may require multiple passes.

Advantages of Knurling

There are different advantages of knurling the tools and objects. Some of important benefits are discussed here:

Enhanced Grip

• Increased friction from knurled surfaces guarantees a firm grip even in slick circumstances.
• It is easier to avoid slippage during assembly or use when items like rollers, wheels, knobs, and bolts are knurled.
• This provides improved control and safety.

Enhanced Aesthetics

• Knurling offers visual curiosity and a distinct texture to items, enhancing their visual attractiveness.
• Aside from its practical benefits, knurling can give things a nice aesthetic appearance.

Paint Adhesion

• Knurling increases surface area and roughness, allowing paint and coatings to stick better to flat surfaces such as plastics or polished metals.
• Knurling improves a material’s surface area, which is advantageous for paint adherence and branding.
• Better paint adherence and longer-lasting results are offered by textured surfaces.

Improved Functionality

• By making things easier to hold and handle, knurling makes tools, handles, and other parts more useful.
• For instance hammers, knifes, axes, and other tools can get knurl which helps to improve its grip and eventually the functionality.

Quick Assembly

• Typically, the flat face of knurled nuts makes them simpler to manually tighten, saving time.
• This can be especially helpful in situations where assembly time is of the essence. For instance, while putting the hose in the hydrants during the time of fire fighting.

Limitations of Knurling

Knurling has some drawbacks which are discussed briefly in this section:

Material Choice

• When knurled, brittle or fragile materials could break or distort. So every material is not suitable for knurling.
• It is crucial to take the material’s flexibility and hardness into account when deciding whether to apply knurling.
• Soft plastics are among the materials that might not withstand the process well and could break or distort.

Surface Defects

• During knurling, improper feeds, speeds, tool condition, or pressure can result in damage including cracks in more brittle materials, inadequate pattern definition, or uneven tracks.
• Scrapping or reworking the component is necessary for defective knurls.

Requirements for Precision

• Creating precise and repeatable knurling patterns can be difficult, particularly for complex geometries or small workpieces.

Inaccuracies in Dimensions

• Aggressive knurling in high quantities might cause minor differences in diameter or surface distortion.
• Close tolerances might be difficult to obtain.
• Secondary processes may be required to resize or resurface knurled components.

Weakened Surface

• Although the knurling procedure strengthens the surface, it can also cause weariness-causing tensions.
• Knurling may degrade the surface or diminish impact resistance in some cases.

Applications of Knurling

There are varieties of industries that use the knurling. Some of the applications of knurling are given here:

Manufacturing Industries

• Components with ridges added by knurling increase the material’s surface friction.
• Assembly connectivity can be improved thanks to the ridges in these parts.
• Pistons, nuts, bolts, and tool handles are a few examples of applications.

Jewelry and Sculpting

• Beautiful knurling patterns can be seen on bands, wedding rings, decorative motifs, and even everyday household items.

Household Products

• Commonly found on home appliances, small knobs and dials improve functionality, grip, and appearance.

Repairs

• Raised portions encircling the indented sections of the rolled-in knurled surface can compensate for component wear.
• Consequently, knurling is still occasionally employed as a repair technique, but it is less popular now since finding replacement components could be a more affordable choice.
• Knurling worn-out piston cylinders to enable continued operation was a widespread practice.

Video Reference

References

• https://www.profiroll.com/fileadmin/user_upload/4_verfahren/5_Bibliothek/Knurling_Rolling.pdf
• https://www.hommel-keller.de/en/zeus/knurling-technology/
• https://monroeengineering.com/blog/what-is-knurling-heres-what-you-should-know/
• https://www.reidsupply.com/en-us/industry-news/what-is-knurling
• https://waykenrm.com/blogs/what-is-knurling/
• https://at-machining.com/knurling-tools-and-techniques/
• https://fractory.com/knurling-explained/#Knurling_Process