Knurling
What is knurling?
Knurling is a type of surface patterning used in machining, where a deliberate roughened pattern is formed on the surface of a rotational part to improve grip and handling. Knurling is usually done on a lathe, either a CNC lathe or a manual lathe, and is a typical operation for example on control knobs, tool handles, bushings, and other hand‑tightened components. With knurling, a regular raised pattern is created on the surface of the part, increasing friction and improving usability in mechanical engineering workshop products.
Knurling is not merely an aesthetic solution; it has a clear functional purpose. It enables better torque transfer by hand without separate tools and reduces slipping, for example in oily or otherwise slippery conditions.
Manufacturing knurling in machining
Knurling can be produced using two main methods: form knurling or cut knurling. The choice of method is influenced by the material being machined, wall thickness, dimensional tolerances, and the intended use of the part.
In form knurling, a knurling wheel is used to press the pattern into the workpiece surface through plastic deformation. No material is removed; instead, it flows and reshapes. This method is common for steels, aluminum, and brass alloys. Form knurling slightly increases the outer diameter of the part, which must be taken into account when defining the nominal dimension and tolerance.
In cut knurling, the pattern is created by removing material with a cutting tool. This method is well suited for thin‑walled parts and for materials where strong compressive force could cause distortion. Cut knurling allows more precise diameter control and is useful, for example, with stainless steel and cast iron.
Knurl patterns and their applications
The knurl pattern has a significant impact on grip, wear resistance, and appearance. The most common pattern types in machine shops are straight, helical, and cross or diamond knurling.
Straight knurling forms grooves perpendicular to the shaft axis. It is suitable where a moderate grip is needed without an overly aggressive surface structure. Helical knurling is made at an angle to the part’s axis and is used, for example, when the intention is to guide finger movement in a rotational direction.
Cross or diamond knurling is formed by combining two opposing helices. This pattern provides very good grip and is common on control knobs, clamping components, and instrument parts. Diamond knurling distributes the load evenly and withstands wear well, which is important in series production in the machining industry.
The importance of knurling in the machining industry
Knurling is a simple yet effective way to increase a product’s functionality without additional components. It reduces the need for rubber coatings or other extra materials and improves ergonomics directly through machining.
In a machine shop, knurling is often a finishing step that combines technical functionality with visual quality. When done correctly, it improves the user experience, increases safety, and enhances the perceived quality of the product.
Summary
Knurling is a regular pattern produced on the surface of a rotational part to improve grip and user comfort. It can be implemented using either form or cut knurling, depending on the material and dimensional requirements.
