Knurling is a manufacturing process that forms regular patterns on a workpiece surface, typically on cylindrical parts using a dedicated knurling tool. It is a surface-forming process rather than a simple surface treatment.
This article provides a comprehensive introduction to types, patterns, and design guidelines, making it easier to choose during the part design process.
What Is CNC Knurling?
CNC knurling is a manufacturing process that produces regular, repetitive patterns on the surface of a workpiece using a CNC lathe or turning center.
It is most commonly applied to the outer surface of cylindrical or rotating parts. During CNC machining, a dedicated knurling tool forms the desired pattern through material deformation or cutting. The pattern is defined by key features such as type, pitch, length, location, and depth.
The main purposes of knurling are to improve grip, prevent slippage, enhance tactile feel, provide mechanical interlocking in certain applications, and improve part appearance.
Why Is Knurling Used on CNC Parts?
Improve Grip and Handling
CNC knurling enhances grip and anti-slip performance by creating regular protrusions and grooves on the surface of parts, thereby creating a textured surface. The effect depends on the knurling pattern, pitch, depth, material, mating surface, etc. Therefore, CNC knurling mainly provides mechanical grip and anti-slip performance through geometric textures rather than simply changing the friction coefficient of the material itself.
Improve Torque Transfer in Certain Applications
In applications such as knurled shafts, hubs, and press-fit components, knurling can increase friction and mechanical contact, helping improve torque transmission. However, for high-load or high-torque applications, you may need keyways, splines, serrations, or interference fits. CNC knurling cannot replace these specialized connection methods.
Provide Better Tactile Feedback
CNC knurling not only changes the appearance of the parts you design but also their tactile feel. When you touch a knurled surface, you can clearly perceive its texture, resistance, position, and rotation. Therefore, knurling can provide more distinct tactile feedback, which is particularly valuable for designs that require precise manual operation.
Types of CNC Knurling
CNC knurling can mainly be classified into three categories: knurling patterns, machining methods, and pitch.
Types of Knurling Patterns by Design
Diamond Knurling
Diamond knurling is one of the most common types of knurling. It is formed by the intersection of two sets of diagonal lines in different directions, creating a diamond pattern. Its main features include good grip, strong friction, a distinct three-dimensional texture, and a recognizable appearance.
It is commonly used on knobs, handles, and other adjustment components. If the part you design requires good finger grip, diamond knurling is a common choice.
Straight Knurling
Straight knurling forms parallel straight lines along the axial direction of the part. It has no intersecting lines and a relatively simple pattern.
Its main features include clear directional lines, a simple appearance, and improved grip. It is suitable for applications that require directional manual operation.
CNC straight knurling is commonly used on shafts, adjustment components, knobs, handles, and other manual operating parts.
Diagonal Knurling
The diagonal knurling pattern extends across the surface of the part at a certain angle. It can be designed with different directions and texture effects according to your requirements. The main feature of diagonal knurling is its directional pattern, which can meet specific gripping or decorative requirements.
If you want to achieve a specific slanted direction for the knurling, you can consider using a diagonal knurling pattern when designing your part.
Types of Knurling by Machining Method
Form Knurling
Form knurling uses a knurling wheel to plastically deform and redistribute the material, forming the desired pattern. It offers high efficiency and is widely used for conventional knurling applications.
Cut Knurling
Cut knurling removes material with a specialized tool to form the desired pattern. It causes less deformation and lower radial force, making it easier for you to control dimensions on tight-tolerance parts.
Types of Knurling by Pitch
Fine-Pitch Knurling
This type of knurling has a denser pattern and a smaller pitch.
Its main features are a fine surface texture, refined appearance, and a relatively smooth feel. It is suitable for smaller parts and is commonly used for precision instruments, small knobs, electronic devices, and components with high appearance requirements.
If your part falls into these categories, you can consider fine-pitch knurling.
Medium-Pitch Knurling
It lies between fine-pitch and coarse-pitch knurling and is a relatively common choice.
This type of knurling enables the parts you design to have good grip performance and a good appearance while achieving a relatively good balance for stable processing.
Coarse-Pitch Knurling
The pattern is relatively distinct, and the pitch is relatively large. The main features of this type of knurling are an obvious surface pattern and strong grip. It is suitable for larger parts and applications that require a significant anti-slip effect.
However, a larger part does not necessarily require coarser knurling. The appropriate pitch should be selected based on the required grip, appearance, and application.
CNC Knurling Process
CNC Part Preparation
Before starting knurling, you need to confirm the part material, dimensions, knurling area, pattern, pitch, and surface requirements based on your drawing. The material’s hardness, ductility, and plastic deformation behavior can also affect the knurling result.
CNC Turning for Basic Dimensions
Knurling is usually performed after the basic turning operations are completed, rather than directly on the raw material. For example, your parts may first undergo CNC turning, internal hole machining, groove machining, and chamfering before knurling. Simply put, you machine the basic dimensions first, followed by the knurling pattern.
Determining the Knurling Area
If your knurling area is too close to these features, the tool may not have enough clearance, causing incomplete knurling, edge deformation, or burrs. Therefore, you should consider both appearance and tool accessibility when defining the knurling area.
Selecting the Right Knurling Tool
Select the knurling tool based on the required pattern, pitch, part diameter, material, and machining method. The tool should also provide sufficient clearance for the knurled area.
Installing and Aligning the Knurling Tool
This is a crucial step in the knurling process for your CNC parts. During machining, the knurling tool needs to be installed correctly to ensure the proper contact position, angle, and tool height relative to the workpiece.
Setting CNC Knurling Parameters
Key parameters, including spindle speed, feed rate, and tool pressure, require you to make adjustments based on the material, knurling method, part geometry, and required pattern.
Performing the Knurling Operation
During machining, your CNC parts rotate on the spindle while the knurling tool contacts the workpiece at the preset position. You need to maintain stable tool contact, appropriate machining parameters, sufficient clamping rigidity, and correct tool positioning.
Deburring After Knurling
After knurling, you need to check for burrs, local deformation, and sharp edges, especially around the edges of the knurled area.
During deburring, make sure not to damage the knurling pattern, so the knurled area requires more careful post-processing.
Dimensional and Visual Inspection After Knurling
After knurling, you need to inspect the parts according to your drawings and quality requirements. Check the outer diameter, knurling length and position, and adjacent features.
For knurling quality, check the pattern, pitch, depth, and any double patterns or omissions. Also check for burrs, scratches, dents, uneven patterns, and surface contamination.
For mass production, you should ensure consistent knurling quality across different batches.
Form Knurling vs Cut Knurling
| Comparison Item | Form Knurling | Cut Knurling |
| Basic Principle | Forms the pattern by deforming the material | Forms the pattern by removing material |
| Material Change | More significant plastic deformation | Mainly material removal with less deformation |
| Radial Force | Typically higher | Typically lower |
| Outer Diameter Change | Requires careful consideration | Generally easier to control |
| Suitability for Thin-Walled Parts | Requires caution | Generally more suitable |
| Suitability for Long, Slender Parts | Deformation and vibration need to be considered | Generally easier to control |
| Material Ductility Requirements | Relatively higher | Generally suitable for a wider range of materials |
| Machining Efficiency | Generally higher | Depends on the tool and machining parameters |
| Tool Type | Knurling wheels | Cut knurling tool |
| Main Risks | Material deformation, dimensional changes, and double tracking | Unstable cutting, burrs, and tool wear |
| Typical Advantages | High efficiency and suitable for conventional knurling | Less material deformation and relatively easier dimensional control |
CNC Knurling Design Guidelines
Define the Knurling Pattern and Pitch
In the drawings you design, clearly define the knurling pattern, length, pitch, and position. Do not simply label it as “knurling,” as the machining supplier may not be able to determine your specific requirements accurately.
Consider Part Wall Thickness and Rigidity
Form knurling generates relatively high radial force. Therefore, for thin-walled, small-diameter, and slender shaft parts, you need to pay special attention to deformation and vibration. When necessary, consider increasing the wall thickness or using cut knurling.
Consider Dimensional Changes
Form knurling can cause plastic deformation of the material, which may affect the final outer diameter. For parts with strict dimensional tolerances, you need to determine at the design stage whether the dimensions before or after knurling should be used as the control dimensions.
Select the Knurling Method
The material will directly affect the knurling result of the CNC parts you design. Aluminum alloys and brass with good ductility are usually suitable for form knurling. For high-hardness materials, thin-walled parts, or parts with dimensions sensitive to deformation, you can consider using cut knurling.
Avoid Overdesigning Knurling
The choice of CNC knurling should be based on its actual function. If the main purpose is to improve grip, prevent slipping, or facilitate manual adjustment, you can select the appropriate pattern and pitch. However, if knurling is mainly for decoration, you should also consider whether it is necessary or whether other surface texturing methods can be used.
Common CNC Knurling Problems
Incomplete or Unclear Knurling Patterns
The knurled area may have problems such as incomplete patterns or inconsistent shades. You can improve it by increasing the rolling pressure, optimizing the processing parameters, replacing worn tools, and ensuring proper tool alignment and workpiece rigidity.
Uneven Knurling Patterns
The knurled area may encounter problems such as one end appearing deeper than the other, local pattern deformation, inconsistent spacing, or different visual effects across the surface. You can improve this by installing the tool correctly, increasing clamping stability, optimizing machining parameters, and ensuring consistent workpiece surface dimensions.
Double or Overlapping Knurling Patterns
Knurled areas may have overlapping, double, or irregular patterns. You can improve this by choosing a knurling wheel with the appropriate size and pitch for the workpiece and ensuring that the knurling wheel is in correct contact with the workpiece.
Dimensional Changes After Knurling
The outer diameter may change after knurling, affecting assembly, clearances, and functional dimensions. For parts with strict dimensional requirements, you should verify the appropriate pre-knurling dimension through testing and control the final dimension after knurling.
Part Deformation
Thin-walled, small-diameter, or low-rigidity parts may experience bending, out-of-roundness, local deformation, or vibration during knurling. In such cases, even if the knurling pattern looks normal, the overall dimensions of your part may still fail to meet the requirements.
Burrs or Deformation at Knurling Edges
The starting and ending areas of the knurled section are more prone to burrs, material buildup, or incomplete patterns. This is especially noticeable when the knurled area is close to end faces, steps, or grooves. Therefore, when designing, you need to allow sufficient machining space for the knurled area and perform appropriate deburring after machining.
Surface Scratches or Dents
Scratches, dents, or other surface defects may occur outside the knurled area. You can improve this by protecting the non-knurled area, controlling the tool contact range, and ensuring stable contact between the tool and the workpiece.
Applications of CNC Knurled Parts
Knobs and Adjustment Components
CNC knurling can improve contact between your fingers and the part surface, making it easier to rotate, adjust, and position the part during use.
If you are designing knobs that require frequent manual operation, such as instrument adjustment knobs, audio equipment knobs, electronic control knobs, industrial equipment adjustment knobs, or camera control rings, a knurled surface usually provides better rotational control than a completely smooth surface.
Handles and Manual Controls
By adding texture to the contact area, knurling can improve grip and reduce the risk of finger slippage during operation.
Knurling can be used on various parts that require manual gripping, such as small handles, adjustment handwheels, tool operating components, and mechanical equipment controls.
Screws, Nuts, and Fastening Components
If your CNC parts are fasteners that need to be tightened or loosened by hand, you can add knurling to the outer cylindrical surface. It makes hand screws, knurled nuts, and other manual fasteners easier to operate, especially for frequent assembly, disassembly, or adjustment.
Shafts and Mating Components
In some mechanical structures, knurling can be applied to shafts, sleeves, hubs, and other mating areas. The texture can increase friction and mechanical interlocking, helping improve connections in certain press-fit or retention applications.
However, you should note that knurling cannot replace keyways, splines, or other high-strength mechanical connections. Its suitability depends on your materials, interference, loads, and specific structure.
Consumer Electronics Components
For metal parts where appearance is important, knurling can also serve as a decorative feature. It is commonly used on aluminum alloy, brass, and stainless steel parts such as camera components, control rings, housings, and other high-end electronic products. With appropriate surface treatment, your parts can achieve a distinct and precise mechanical texture.
FAQ
Q: What Materials Can Be Knurled?
A: Aluminum, brass, stainless steel, and some engineering plastics can be knurled, depending on their hardness, ductility, and the selected knurling method.
Q: Does Knurling Change the Part Diameter?
A: Yes. Form knurling can change the final diameter due to material deformation.
Q: What Are the Differences Between Manual and CNC Knurling?
A: Manual knurling relies on operator skill, while CNC knurling offers better consistency and repeatability.
Q: What Are the Best CNC Knurling Tools for Precision Metalworking?
A: The best tool depends on the knurling method, pattern, pitch, material, and part geometry. For precision parts, the tool should provide stable contact and sufficient wear resistance to maintain consistent patterns.
Q: What Tolerances Can Be Achieved with CNC Knurling?
A: The specific tolerance depends on the material, knurling method, part structure, and processing requirements, and needs to be evaluated based on your drawings.
Final thoughts
Shanghai Yecheng provides professional CNC precision machining services. Based on your drawings and specific requirements, we can select the appropriate knurling process and strictly control dimensions, knurling patterns, and surface quality. With extensive CNC machining experience and a comprehensive quality inspection process, we are committed to providing customers with consistent and reliable custom knurled parts.
