Knurling is a method used to cut or roll a pattern in a material such as plastic or metal. This process is normally performed on a lathe, although in some cases a manual knurling tool is used. A serrated object can have a diamond, cross, or straight line pattern that adds functionality and pleasing aesthetics. Knurling is often intended to provide a better gripping surface than the raw material, and knurled patterns are often found on handles, buttons, and other similar items. Another use for the process could be to put a worn out part into service, for example as the piston skirts of the internal combustion engine used to be fluted to increase performance.
The main method used for knurling objects is a lathe process that uses a very hard roller to press the desired shape into the work material. A roll with a reverse impression of the desired boss is held in a joint or template and then pressed against the workpiece. The main configurations used for this type of knurling contain one or two rollers. A straight serration can be pressed by a roller, but any diamond or cross pattern will require rollers with opposing patterns. The downside to this process is that the rollers need to be adjusted to the unique outside diameter of each part, so it’s best for mass production of many identical components.
Another lathe process is similar to that used in cutting screw threads. This method can be used to create a diamond pattern by essentially cutting the left and right strands on the same object. In this case, the knurling process is typically accomplished using a self-feeding lathe and a variety of cutting attachments. Unlike the lamination method, a single cutting attachment can be configured to knurl a wide variety of different workpieces.
A third way to knurl an object is with hand tools. These hand knurling tools work in the same way as pipe cutters, but are designed to press a pattern into the workpiece rather than cutting it. Most hand knurling tools contain three wheels, one of which will have an opposite pattern to the other two. The benefit of this process is that the tool needed can normally be carried to the job site, rather than taking the part to a large, stationary lathe.