Knurling Process: Types, Tools and Finishes Explained

If you’ve ever picked up a metal tool and noticed that textured grip on the handle, you’ve already seen knurling in action. It’s one of those processes that looks simple from the outside, but once you get into production—especially CNC machining—you realize there’s quite a bit going on behind it.

Knurling isn’t just about appearance, especially in precision CNC machining applications. In most cases, it’s there for a reason: better grip, tighter assembly, or even just making a part feel more “finished,” as discussed in practical knurling applications and uses. The challenge is doing it cleanly and consistently, especially when you’re working with different materials or tight tolerances.

What Is Knurling

Knurling is a manufacturing process where a patterned texture is pressed into the surface of a metal part, as described in this overview of knurling process basics. Unlike cutting or milling, it doesn’t remove material. Instead, it displaces it.

That distinction matters. Because the material is being pushed and reshaped rather than cut away, the diameter of the part actually increases slightly after knurling. This is something people often overlook during design, especially when considering CNC machining tolerances.

A common example is a metal knob. Without knurling, it would be smooth and hard to grip, especially with oily or wet hands. Add a diamond knurl pattern, and suddenly it’s much easier to handle.

You’ll also see knurling used in press-fit applications. The raised pattern increases friction, helping parts stay securely in place without additional fasteners.

How the Knurling Process Works in Practice

Basic Principle of Knurling

At its core, knurling works by pressing hardened steel wheels (called knurl wheels) into a rotating workpiece. As the wheels roll over the surface, they imprint their pattern onto the material.

Because this is a forming process, the material flows under pressure. Softer materials like aluminum or brass respond well, while harder materials require more force and careful setup.

Step-by-Step Knurling Workflow

In a typical setup, the process starts with preparing the workpiece. Diameter matters here, because certain sizes work better with specific knurl pitches.

Next comes machine setup. Most knurling is done on a lathe, whether manual or CNC. The tool is mounted, aligned, and brought into contact with the part.

Pressure is applied gradually. Too much pressure too quickly can damage the pattern or even the tool. Too little, and the pattern won’t form properly.

Once the knurl is formed, the part is inspected. A clean, consistent pattern is the goal. If the lines look doubled or uneven, something in the setup likely needs adjustment.

In real production, operators often rely on experience as much as theory. Small adjustments in pressure or speed can make a big difference.

Key Parameters That Affect Knurling Quality

This is where things can go wrong—or right.

Speed is one of the first variables to consider. If the spindle speed is too high, the tool may slip instead of forming a clean pattern. Slower speeds usually produce better results.

Feed rate also plays a role. A steady, controlled feed helps maintain consistency across the surface.

Pressure is critical. Insufficient pressure leads to shallow, unclear patterns. Too much pressure can deform the part or wear out the tool prematurely.

Material choice makes a big difference as well. Brass is often considered ideal because it forms clean patterns with relatively low force. Stainless steel, on the other hand, can be challenging and may require more robust tooling.

In practice, there’s no single “perfect” setting. It’s often a matter of dialing things in based on the material and desired finish.

Types of Knurling Patterns

Straight Knurling

Straight knurling produces parallel lines along the surface. It’s less common than other types but still useful in certain applications, especially where alignment matters.

Diamond Knurling

This is the pattern most people recognize. The crisscross design creates a strong grip, making it ideal for handles, knobs, and tools.

If you’re unsure which pattern to choose, diamond knurling is usually a safe default. It works well in most situations and provides reliable performance.

Diagonal Knurling

Diagonal patterns run in a single direction. They’re often used for decorative purposes or in specialized applications where a directional texture is needed.

Form Knurling vs Cut Knurling

Not all knurling is done the same way.

Form knurling is the most common method. It presses the pattern into the material, displacing it outward. This method is fast and efficient, which is why it’s widely used in production.

Cut knurling, on the other hand, removes material instead of displacing it. It’s more precise and produces less deformation, but it’s slower and requires more control.

If you’re working on high-volume parts, form knurling is usually the better choice. For more precise or delicate applications, cut knurling may be worth considering.

Knurling Tools and Equipment

Types of Knurling Tools

The most basic tools use one or two knurl wheels mounted in a holder, as commonly used in industrial knurling tools and applications. These wheels come in different patterns and pitches.

There are also bump-style tools, which press directly into the material, and scissor-style tools, which apply pressure from both sides. The latter can reduce stress on the machine.

Tool Selection Tips

Choosing the right tool depends on several factors.

Material is one of the biggest. Softer metals require less aggressive tooling, while harder materials need stronger, more durable tools.

Pattern choice matters too. The wheel must match the desired finish.

In CNC setups, stability is key. Poor-quality tools or improper mounting can lead to inconsistent results. It’s usually worth investing in good tooling upfront.

Knurling Finishes and Surface Quality

Standard Knurling Finishes

Knurling patterns are often described as coarse, medium, or fine. The difference comes down to the pitch of the pattern.

Coarse knurls are deeper and more pronounced, offering better grip. Fine knurls are more subtle and often used for smaller parts.

What Defines a Good Knurl Finish

A good finish is consistent and well-defined. The pattern should be sharp, evenly spaced, and free of defects.

If you see double lines or uneven spacing, it usually points to setup issues.

Post-Processing After Knurling

After knurling, parts often go through additional steps.

Deburring is common, especially to remove sharp edges.

Cleaning helps remove any residual oil or debris.

In some cases, surface treatments like plating or coating are applied to improve corrosion resistance or appearance.

Materials Suitable for Knurling

Not all materials behave the same.

Aluminum is easy to knurl and produces clean results with minimal effort.

Brass is often considered one of the best materials for knurling. It forms sharp patterns and is easy on tools.

Steel is more challenging and requires more force.

Stainless steel can be difficult, especially if the setup isn’t optimized. It tends to resist deformation, which can lead to poor pattern formation.

If you’re just starting out, working with brass is usually the easiest way to get consistent results.

Common Applications of Knurling

Knurling shows up in a wide range of products.

Grip-related components are the most obvious. Tool handles, knobs, and control dials all benefit from the added texture.

In mechanical assemblies, knurling is often used to improve friction in press-fit parts.

There are also decorative uses. Some consumer products use knurling purely for aesthetics, giving parts a more refined or industrial look.

A good example is camera equipment. Many adjustment knobs use fine knurling to balance grip and appearance.

Knurling Process in CNC Machining

In CNC machining, knurling is usually integrated into turning operations.

The part is already rotating, so adding a knurling tool is straightforward. This makes it efficient for both small batches and large production runs.

Automation also improves consistency. Once the parameters are set correctly, CNC machines can produce uniform results across multiple parts.

For manufacturers, this means less variation and fewer rejects.

Common Knurling Problems and How to Fix Them

Even with the right setup, issues can still happen.

Double tracking is one of the most common problems. It happens when the pattern doesn’t align properly. Adjusting the diameter or tool pitch usually fixes it.

Shallow patterns often result from insufficient pressure. Increasing force gradually can help.

Material tearing can occur with harder metals or incorrect speeds. Slowing things down and using proper tooling can reduce this issue.

Tool wear is another factor. Worn knurl wheels won’t produce clean patterns, so regular inspection is important.

How to Choose the Right Knurling Method

Choosing the right approach depends on your priorities.

If you need grip and speed, form knurling is usually the way to go.

If precision is more important, cut knurling may be a better option.

Material, production volume, and cost all play a role. There’s rarely a single “best” method—just the one that fits your specific application.

If you’re unsure which knurling method is right for your part, you can contact our team to review your design and requirements. We can help you select the most suitable process based on your material, tolerance, and production needs, and provide a fast quotation for your project.

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