Lathe knurling
Lathe knurling is a process in which a knurling tool is used to create a pattern on the surface of a workpiece during lathe machining. The purpose is to increase friction on the workpiece surface, making it easier to grip or aesthetically pleasing. Knurling is widely used in the manufacture of various tools, handles, knobs, and other parts, such as wrenches, machine tool operating handles, and instrument knobs. Knurling patterns primarily include straight, reticulated, and twill. Straight patterns are parallel to the workpiece axis, while reticulated patterns are formed by intersecting perpendicular straight lines in a diamond pattern, with the twill lines forming a certain angle with the axis. The knurling process does not require material removal, but rather creates a concave and convex pattern on the workpiece surface through plastic deformation of the metal. Therefore, the basic dimensions of the workpiece are not altered, and only a certain plastic deformation layer is produced on the surface.
The tool used for knurling on a lathe is the knurling cutter. Its structure and type have a significant impact on knurling quality. The knurling cutter consists of a cutter body and a knurling wheel. The knurling wheel surface has a tooth profile corresponding to the desired pattern. Commonly used knurling wheel tooth profiles are 60° and 90°. Based on the number of knurling wheels, knurling cutters can be divided into single-wheel knurling cutters, double-wheel knurling cutters, and six-wheel knurling cutters. Single-wheel knurling cutters have a single knurling wheel and are used to produce straight patterns. Double-wheel knurling cutters consist of two intermeshing knurling wheels with left-handed and right-handed tooth profiles, respectively, which can produce reticulated patterns. Six-wheel knurling cutters are equipped with three sets of double-wheel knurling cutters of different specifications, allowing for easy replacement of knurling wheels to accommodate different patterns and pitch requirements. The pitch of the knurling wheel is an important parameter. Commonly used pitches are 0.5mm, 0.8mm, 1.0mm, 1.2mm, 1.5mm, 2.0mm, etc. The larger the pitch, the rougher the pattern and the greater the friction.
The knurling process on a lathe requires appropriate operating procedures and parameter settings to ensure a clear, uniform pattern and prevent workpiece deformation. Before processing, the workpiece must be prepared, securely clamped, and radial runout corrected to ensure stable rotation during the knurling process. The knurling cutter must be accurately installed, the toolholder securely fixed, and the axis of the knurling wheel parallel to the workpiece axis to avoid tilting or pattern distortion during knurling. When starting knurling, the knurling cutter should be brought into contact with the workpiece surface slowly while applying appropriate pressure. Once the pattern is initially formed, the feed should be evenly applied. The spindle speed should be kept within a range of 100-300 rpm during knurling. Excessively high speeds can lead to increased wear on the knurling wheel and unclear patterns. Excessively low speeds can prolong the stress on the workpiece surface and easily cause deformation. The feed rate is typically selected based on the pitch, with larger pitch patterns requiring a higher feed rate, typically 0.2-0.5 mm/min.
Various problems can easily arise during the knurling process on a lathe, requiring appropriate solutions to ensure machining quality. Common issues include unclear patterns, irregular patterns, workpiece deformation, and rapid knurling wheel wear. Irregular patterns are often caused by insufficient pressure, knurling wheel wear, or improper spindle speed . Solutions include increasing pressure, replacing the knurling wheel, or adjusting the spindle speed. Ragged patterns can be caused by tilted knurling cutters, excessive workpiece runout, or uneven feed. These problems require reinstalling the knurling cutters, aligning the workpiece, or maintaining a consistent feed. Workpiece deformation often occurs with thin-walled or slender parts. The high radial pressure during knurling can easily cause the workpiece to bend or ellipse. These problems can be addressed by increasing workpiece support, reducing knurling pressure, or performing knurling in multiple steps. Rapid knurling wheel wear is primarily caused by excessive pressure, a hard workpiece material, or an unsuitable knurling wheel material. Pressure should be properly controlled. Hard materials can be annealed first, and knurling wheels with high wear resistance, such as high-speed steel or carbide, should be selected.
Post-knurling quality inspection and subsequent processing are also crucial steps in the lathe knurling process. Quality inspection primarily examines the clarity, uniformity, and continuity of the pattern, as well as the dimensional and shape accuracy of the workpiece. The pattern should be clearly discernible, free of broken or irregular lines, and the cross-sectional angles of the patterns should be uniform and consistent. Use a caliper or micrometer to measure the diameter of the workpiece after knurling. Due to plastic deformation during knurling, the diameter will increase slightly, typically by 0.1-0.3mm, ensuring this is within the acceptable range. For workpieces with specific fit requirements, the fit accuracy must also be checked for any impact. The knurled workpiece may have burrs on its surface, requiring deburring. Sanding or filing can be used to minimize scratches during use. For workpieces requiring rust protection, anti-rust treatment, such as oiling or electroplating, should be applied after knurling to extend its service life. Strict quality inspection and appropriate subsequent processing ensure the quality and performance of knurled workpieces.
