Choosing the right types of knurling is important when designing CNC machined components. A knurled surface can improve grip, support press-fit assembly, increase friction, or simply improve appearance.
However, not every knurling pattern works equally well for every part.
Straight knurling, diamond knurling, and diagonal knurling each have different functions. In addition, pitch, depth, material, and part geometry all affect the final result.
Therefore, engineers should select the knurling pattern based on function instead of appearance alone.
This guide explains the main types of knurling, their differences, applications, and machining considerations.
What Is Knurling?
Knurling is a machining process that creates a repeated pattern on the surface of a cylindrical component.
The pattern is normally formed on a lathe or CNC turning machine.
Instead of producing a completely smooth surface, the knurling tool creates raised and recessed features around the outside diameter.
Knurling is commonly used on:
- Control knobs
- Tool handles
- Adjustment screws
- Fasteners
- Metal inserts
- Shafts
- Thumb screws
- Electronic components
- Automotive components
- Industrial fittings
The pattern may be used for grip, assembly, positioning, or decoration.
In CNC machining, the geometry of the knurl must match the part diameter, material, and final function.
What Are the Main Types of Knurling?
The most common types of knurling include:
- Straight knurling
- Diamond knurling
- Diagonal knurling
- Cross knurling
- Special decorative knurling
For most industrial CNC components, straight, diamond, and diagonal patterns are the most common.
Each pattern creates a different contact surface.
Therefore, selecting the correct pattern can improve part performance and reduce manufacturing problems.
1. Straight Knurling
Straight knurling creates parallel grooves that run along the axis of the component.
The grooves do not cross each other.
This type of knurling is often used when the part needs controlled axial grip or interference during assembly.
Common applications include:
- Press-fit components
- Metal inserts
- Pins
- Shafts
- Adjustment parts
- Handles
Straight knurling can also help prevent rotation between two assembled components.
For example, a knurled metal insert may be pressed into a plastic or metal housing.
The raised pattern increases mechanical engagement.
Advantages of Straight Knurling
Straight knurling offers several benefits:
- Simple pattern
- Good rotational resistance
- Suitable for press-fit parts
- Relatively easy to inspect
- Useful for functional assemblies
However, the final outside diameter may increase after knurling.
Therefore, engineers should consider the finished knurled diameter when defining tolerances.
2. Diamond Knurling
Diamond knurling is one of the most recognizable types of knurling.
The surface contains two diagonal groove directions that cross each other.
This creates a diamond-shaped pattern.
Diamond knurling is widely used when strong hand grip is required.
Typical applications include:
- Tool handles
- Adjustment knobs
- Thumb screws
- Equipment controls
- Machine handles
- Precision instruments
Because the diamond pattern provides grip in several directions, it is often more effective than straight knurling for manually operated components.
Advantages of Diamond Knurling
Diamond knurling can provide:
- Strong hand grip
- Good friction in multiple directions
- Attractive industrial appearance
- Reliable surface texture
- Good control during manual adjustment
However, aggressive diamond knurling can feel uncomfortable if the pattern is too sharp.
Therefore, pitch and depth should match the application.
A fine diamond pattern may be better for small knobs. In contrast, a coarse pattern may work better for large industrial handles.
3. Diagonal Knurling
Diagonal knurling uses grooves that run at an angle around the component.
Unlike diamond knurling, the grooves normally run in only one diagonal direction.
Diagonal patterns are less common than straight or diamond knurling, but they can still be useful in certain mechanical applications.
Typical uses include:
- Specialized grips
- Rotating controls
- Decorative CNC parts
- Industrial components
- Directional friction surfaces
The groove direction can influence how the user grips or rotates the part.
Therefore, diagonal knurling may be selected when a directional surface is useful.
Types of Knurling Compared
The following table gives a simple comparison.
| Knurling Type | Pattern | Main Function | Common Applications |
|---|---|---|---|
| Straight | Parallel grooves | Prevent rotation or improve press fit | Inserts, shafts, pins |
| Diamond | Crossed grooves | Improve hand grip | Knobs, handles, thumb screws |
| Diagonal | Angled grooves | Directional grip or appearance | Controls, specialty parts |
| Fine knurl | Small pitch | Precision grip | Electronics, small knobs |
| Coarse knurl | Large pitch | Strong grip | Industrial handles |
The best choice depends on how the component will be used.
Types of Knurling for Better Grip
When grip is the main requirement, diamond knurling is usually one of the most common choices.
Because the raised pattern provides contact in multiple directions, the user can hold and rotate the part more easily.
However, grip strength also depends on:
- Knurl pitch
- Knurl depth
- Part diameter
- Surface hardness
- Material
- Coating
- Final surface treatment
A very deep knurl is not always better.
For example, a deep coarse pattern on a small adjustment knob may feel too aggressive.
Therefore, the pattern should match the size and use of the component.
Types of Knurling for Press-Fit Components
Straight knurling is often more suitable for press-fit assemblies.
The raised ridges can increase interference between the knurled part and the mating hole.
This is especially useful for:
- Inserts
- Pins
- Shafts
- Bushings
- Mechanical connectors
However, engineers must control the knurl diameter carefully.
If the knurled diameter becomes too large, insertion force may increase significantly.
As a result, the mating component may deform or crack.
Therefore, press-fit knurling requires accurate control of:
- Original diameter
- Knurl depth
- Finished diameter
- Hole tolerance
- Material strength
- Assembly force
For precision parts, CNC machining and inspection should consider the assembled condition instead of checking only the individual component.
Fentor Mold provides components manufacturing for custom machined parts and mold-related components.
Knurl Pitch: Fine vs Coarse
Pitch describes the spacing between the teeth or grooves of the knurl pattern.
It has a major effect on grip and appearance.
Fine Knurling
Fine knurling uses closely spaced grooves.
It is often suitable for:
- Small-diameter parts
- Precision adjustment knobs
- Electronic components
- Light manual grip
- Decorative parts
Fine knurling usually creates a cleaner and more refined appearance.
Coarse Knurling
Coarse knurling uses larger spacing.
It is often suitable for:
- Heavy-duty handles
- Industrial equipment
- Large knobs
- Parts used with gloves
- Components requiring stronger grip
However, coarse knurling creates larger surface deformation.
Therefore, the tool, material, and wall thickness must be considered.
How Material Affects Knurling
Material has a major effect on knurling quality.
Different metals respond differently when pressure is applied during the knurling process.
Common knurled materials include:
- Aluminum
- Stainless steel
- Carbon steel
- Brass
- Copper
- Tool steel
Aluminum
Aluminum is relatively easy to knurl.
However, soft aluminum can deform if the pressure is too high.
A clean tool and stable machining setup are important for maintaining a consistent pattern.
Stainless Steel
Stainless steel requires more force.
It can also work-harden during machining.
Therefore, rigid tooling and suitable cutting conditions are important.
Carbon Steel
Carbon steel usually provides good knurl definition.
However, tool pressure must still match the hardness of the material.
Brass
Brass can produce very clean knurling.
It is often used for knobs, inserts, fittings, and decorative components.
Form Knurling vs Cut Knurling
There are two common ways to create knurled surfaces.
Form Knurling
Form knurling presses the pattern into the material.
The tool displaces the surface instead of removing large amounts of metal.
Advantages include:
- Fast processing
- Strong surface pattern
- Suitable for many production parts
However, the process creates high radial force.
Thin-wall components may deform.
Cut Knurling
Cut knurling removes material to generate the pattern.
It usually creates less radial force than form knurling.
Therefore, it can be useful for:
- Thin-wall parts
- Large-diameter components
- Harder materials
- Precision components
However, tool setup is more critical.
The best method depends on material, geometry, tolerance, and production volume.
Common Knurling Problems in CNC Machining
Poor knurling can create several defects.
Common problems include:
- Double tracking
- Uneven teeth
- Incomplete pattern
- Excessive deformation
- Poor surface finish
- Oversized diameter
- Burrs
- Tool marks
Double Tracking
Double tracking happens when the knurl wheel does not follow the same pattern correctly.
The result can look like overlapping or distorted teeth.
This may happen because of an incorrect relationship between:
- Part diameter
- Knurl pitch
- Tool position
- Feed rate
Accurate setup helps reduce this problem.
Excessive Material Deformation
Form knurling applies significant pressure.
If the wall is too thin, the component may become distorted.
Therefore, thin-wall parts require special attention.
Burr Formation
Sharp edges can create burrs after knurling.
Adding proper chamfers before or after machining can improve the final result.
Knurling Diameter and Tolerance
One common mistake is ignoring the diameter increase caused by form knurling.
When the tool displaces material, some of the metal moves outward.
As a result, the finished outside diameter can become larger than the original turned diameter.
This is important for parts that must:
- Fit inside another component
- Pass through a hole
- Maintain clearance
- Match an assembly tolerance
Therefore, drawings should clearly specify whether the dimension refers to the pre-knurl or finished knurl diameter.
This small detail can prevent major assembly problems.
How to Select the Right Types of Knurling
The correct pattern should start with the function of the part.
Consider the following factors.
Grip Requirement
If the user needs strong grip in multiple directions, diamond knurling is often suitable.
Assembly Requirement
If the purpose is to prevent rotation in a press-fit assembly, straight knurling may work better.
Part Diameter
Small components normally require finer patterns.
Large components can often use coarser patterns.
Material
Soft aluminum and hard stainless steel require different tool pressure and machining conditions.
Wall Thickness
Thin-wall components may deform under form-knurling pressure.
Appearance
Some products also require a clean and uniform cosmetic surface.
In this case, consistent pitch and tool alignment become especially important.
Knurling Design Tips for CNC Machined Components
Several design decisions can improve machining stability.
First, leave enough space near shoulders and adjacent features.
Second, avoid placing aggressive knurling on very thin walls.
In addition, define the required knurl type clearly on the drawing.
It is also useful to specify:
- Pattern type
- Pitch
- Knurled length
- Finished diameter
- Tolerance
- Surface treatment
- Functional requirement
If the knurl is only cosmetic, state this clearly.
However, if it is used for press fitting or torque transmission, the functional requirement should be included.
This helps the manufacturer select the correct machining process.
For projects combining precision machined parts with custom tooling, Fentor Mold also provides custom injection mold manufacturing and related component machining support.
You can visit the Fentor Mold homepage for more information about our manufacturing capabilities.
Final Thoughts
Different types of knurling serve different purposes.
Straight knurling is often suitable for press-fit components and rotational resistance. Diamond knurling is commonly used when strong manual grip is required. Diagonal knurling can provide directional grip or a specific surface appearance.
However, the pattern alone is not enough.
Pitch, depth, material, wall thickness, diameter, and machining method all affect the final result.
Therefore, engineers should define both the knurl pattern and its functional requirement before CNC machining begins. A clear specification can improve surface quality, dimensional accuracy, assembly performance, and production consistency.