What Is Knurling?

Knurling is a machining process that produces a patterned texture on the surface of a (typically cylindrical) part by pressing or cutting a hardened tool into the material. It is most commonly applied using CNC turning. 

It is usually used to prevent slipping and improve torque, but some engineers choose to add it just for the look. Think of the crisscrossed grip on a barbell, the ridged surface of a tool handle, or the patterned knob on a stereo—those are all knurled features.  

Knurling is not typically used on mating or precision-fit surfaces, like the contact points of a bolt and nut or a pipe fitting, because the raised pattern can interfere with the tight tolerances required. That’s why you’ll often find it on user-facing components where grip and control matter more than a perfect fit. When you see a knurled dial or tool handle, that texture helps users interact with the product more effectively. 

Have a part you’d like knurled? This service is available by request through Protolabs Network. Contact your account manager or [email protected] to get started. 

How Knurling Works 

Knurling works by pressing a patterned tool against a spinning part to create a textured surface. This is called a forming process, because it shifts material instead of removing it. It’s most often done on a lathe using a hardened roller that embosses the pattern as it moves along the part. 

In some cases, especially with harder materials, a cut knurling method is used. This actually removes material to form the pattern. This is used when you need a very crisp texture or are working with thin-walled or brittle components. 

A few key factors affect how the knurling turns out:

• Tool pressure: More pressure means a deeper pattern
• Feed rate: Controls the spacing and alignment of the texture
• Material hardness: Softer metals knurl easily, but if it is too soft, you can lose detail
• Tool shape and pitch: Determines how the pattern looks and feels 

Forming knurling will slightly increase the diameter of your part, so keep that in mind, particularly if the knurled area needs to fit with another component. 

Types of Knurling Patterns 

Each knurling pattern offers different grip characteristics and aesthetic style. The right choice depends on how you want it to look and what you need it to do. 

Diamond knurling is the most common because it offers grip in multiple directions. Straight knurls are more likely to be used on parts designed to slide in and out without rotation. Diagonal knurls are mainly aesthetic and less pronounced.  

Knurling Methods: Manual vs. Machine 

The method used depends largely on production volume, precision requirements, and available equipment. 

Manual knurling  

This method is typically done on a manual lathe, using a handheld or lathe-mounted knurling tool. It requires operator skill to maintain consistent pressure and feed.  

Machine knurling 

This technique is often done on CNC lathes or turning centres, uses automated tool paths and pressure control to achieve consistent, repeatable results.  

Surface Finish Considerations 

Knurled surfaces are intentionally rough, which makes them excellent for grip, but also more complex when it comes to finding the right surface finish. 

Can knurled parts be anodised or painted?  

Yes, but coatings may build up unevenly due to the peaks and valleys of the pattern. Anodising works well on aluminium knurled parts, but you may lose some of the finer details. 

Can they be cleaned or polished?  

Yes, though aggressive polishing may blunt the knurl. Light tumbling or bead blasting can clean debris without removing the pattern. 

What finishes can be applied? 

Ultimately, you are looking for a finish that conforms to the geometry rather than filling it in.  

Benefits of Knurling 

Knurling may seem like a minor detail, but engineers know that small details can make a huge difference and knurling can have a major impact on how a part performs in the real world. When done right, it can improve the way a user interacts with a product, particularly when parts need to be turned, twisted, or held securely. 

Knurling delivers several advantages spanning look, feel and function.  

Designing for Knurling 

When adding knurled features, a few design rules can help get you better results. 

Also think about the orientation of the knurled surface. It should be easy for the operator to access and should not interfere with threads, seal areas, or other precision features. 

If you’re outsourcing production, include detailed drawing notes specifying knurl type, pitch, and location. CAD models don’t always need to show the pattern geometry. Clear annotation is usually enough. 

Cost of Knurling 

In most cases, knurling adds minimal cost, but it’s worth checking whether your part design introduces complexity that could drive the price up. 

Cost drivers include: 

The more integrated the knurling is into the machining process, the more cost-effective it tends to be. Automated lathe operations can add knurling with little added cycle time. 

Where Is Knurling Used? 

Knurling comes into play wherever grip, control, or feel is critical to how a part performs. If a user needs to hold, twist, or turn something with confidence, knurling gets the job done, so it appears across a wide variety of industries. 

Knurling is especially valuable in safety-critical or hands-on environments, like manufacturing floors, operating theatres, or vehicle interiors, where a slippery surface could have serious consequences and grip can’t be compromised. 

Knurl Your Part  

Curious about knurling your parts? This service is available by request through Protolabs Network. Contact your account manager or [email protected] to get a free quote.