Knurling – Process, Common Machines, Tools, & Applications

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Knurling is a manufacturing process where geometric patterns roll onto a material. These patterns improve grip, increase friction, or repair worn-out parts. In this article, you will learn about the knurling process, common machines, tools, and applications. 

Knurling Process

Hand knurling and machine knurling are the two most common methods of this process. The most basic way is hand knurling, which requires only a small roller tool. When a worker runs the tool across the surface of a workpiece, it leaves a textured pattern indented onto the tool.

On the other hand, a machine provides a more time-consuming process that requires the use of a lathe. First, the workpiece secures directly on a lathe. Then, knurling tools secure on a knurl holder and attach to the worktable. Machine knurling contacts the workpiece to create the required knurl pattern.

Common Machines

Lathe machine parts
Courtesy: Pinterest

Knurling typically occurs on a lathe. A metal lathe, also known as a metalworking lathe, provides precise machining of relatively hard materials. They processed only metals initially, but with the introduction of plastics and other materials and their natural adaptability, they are now employed in a wide range of applications and materials. They are commonly referring to as lathes or by more particular subclass names in machining jargon where the greater context is already recognize (toolroom lathe, turret lathe, etc.). These stiff machine tools, such as tool bits and drill bits, remove material from a rotating workpiece by the movements of various cutting tools (usually linear).

Knurling Tools

Knurling tools produce straight, diagonal, or diamond patterns, having teeth of uniform pitch on cylindrical surfaces. There are many types of tools. Examples include:

  • internal knurling holders
  • convex knurl tools
  • conical knurl tools

An internal knurling holder tool knurls up to a prescribed depth.

knurling tool
Courtesy: IndiaMart

A convex knurl tool is an axial feed tool that possesses a sharp leading edge to spread out the loading. They provide a smooth and precise finish.

convex knurl tool
Courtesy: Practical Machinist

A conical tool generates radial face knurling or conical surfaces to the workpiece, typically for decorative purposes.

conical knurl tool
Courtesy: Accu Trak


Grip Enhancement

Lathe project for a hammer
Courtesy: Holbrook Tech – Weebly

Knurling increases the performance and usefulness of products that require grasping, such as hand tools. When holding and using a hammer with a smooth grip, the user’s hand may slip. Thus, by providing an irregular pattern that allows for a firmer grip, knurling protects against hand slippage.

This type of application applies to tool handles, mechanical pencils, pistol grips, barbell bars, the gripping surface of a motorbike handlebar, and electronic equipment control knobs. Other examples include dart handles and BMX bicycle footpegs.

As a Repair Method

Because raised portions surround depressed sections on a rolled-in knurled surface, these raised areas can compensate for wear on the part. This repair procedure was practicable on pistons of internal combustion engines when labor was cheap, and components were expensive. As such, the skirt of a worn piston extends back to the nominal size using a knulling process. However, the application has become less common as vehicle parts have become less expensive. Also, many performance engine builders actively oppose its use.

Low Precision Assembly

Stainless Shaft with knurling process
Courtesy: Best Fit Precision Co.,LTD

Knulling can also be use when a component assembles into another component as part of a low precision assembly. Such an example is a metal pin into a plastic molding. The outer surface of the metal pin is knurled, so the raised detail “bites” into the plastic irrespective of whether the size of the hole in the plastic closely matches the diameter of the hook.


Mechanical pencils with knurled grip
Courtesy: Reddit

Many surgical tools include this material used for instrument identification and cleaning. Another example is the knurled nut, which has a knurled finish instead of hexagonal or square edges to aid in tightening or loosening the nut without the need for a tool. Thanks to the textured surface, the nut, sometimes known as a thumb nut, may be held between the thumb and fingers. It’s used chiefly on bolts with tiny diameters. Electrical components, musical instruments, and automobiles also require knurled nuts.

Knulling not only adds utility to an object (valve repairs and handgrips are two examples), but it also adds an aesthetic pattern to the material. Knurling can improve its attractiveness by providing an appealing design to a product’s surface. As such, many people feel that textured finishes are more attractive than smooth ones. There are functional reasons for manufacturing organizations to do knurling aside from aesthetics.