Cone turning method
Cones are common geometric shapes found in mechanical parts. They offer advantages such as high centering accuracy and easy disassembly, making them widely used in machine tool spindles, tool tapers, valve spools, and other components. The main methods for turning cones include rotating a small slide, offset tailstock, tracking, and broad-blade turning. Each method has its own unique scope of application and processing characteristics, and the appropriate method should be selected based on factors such as the cone’s size, required precision, and production batch size. Understanding the key methods and processes for turning cones is crucial for ensuring quality and improving production efficiency.
The rotating slide method is one of the most commonly used methods for turning cones. It is suitable for turning cones with shorter lengths and larger angles (such as cones with a taper of 1:5 to 1:30). It is particularly suitable for turning cones whose conical surface intersects the workpiece axis near the spindle bearing. The working principle is to rotate the slide around the axis of the turntable by a certain angle so that the tool feed direction is parallel to the cone’s generatrix. The tool feed is achieved by manually turning the slide handle, thereby turning the desired cone. The angle of rotation of the slide should be equal to the cone’s half-angle, which can be calculated based on the cone’s taper. The rotating slide method is simple to operate and can turn cones of any angle, including internal and external cones. However, due to manual feed, the feed rate is uneven, and the machined surface roughness is relatively high. It is suitable for single-piece, small-batch production, and for cone machining with low precision requirements.
The offset tailstock method is suitable for turning long, small-taper external tapers (e.g., tapers with a taper range of 1:100 to 1:2000), such as those on machine tool spindles and long tapered shafts. The working principle is to offset the tailstock’s upper slide laterally relative to the base by a certain distance, so that the workpiece axis forms an angle with the lathe spindle axis (i.e., the half-angle of the taper). Automatic feed is then used to move the tool along the spindle axis, thereby turning the taper. The tailstock offset can be calculated based on the taper’s length and taper using the formula: offset = (cone length × taper) / 2. The offset tailstock method enables automatic feed, resulting in high surface quality and production efficiency. However, it can only turn external tapers and cannot handle tapers with large tapers. It is therefore suitable for machining medium- and long-length tapers in mass production. When using the offset tailstock method, care should be taken to avoid excessive tailstock offset, as this can affect the lathe’s accuracy and lifespan.
The backing method is a method for high-precision cone machining in mass production. It is suitable for turning internal and external cones of various tapers, and is especially suitable for turning cones with longer lengths and high precision requirements. The backing method mainly consists of a backing, a slider, a bracket, and a tool holder. The angle of the backing is equal to the half-angle of the cone to be machined. The slider is in contact with the backing. When the tool holder feeds longitudinally, the slider slides along the backing, driving the small slide to move horizontally, so that the tool’s motion trajectory is parallel to the centerline of the cone, thereby turning out the cone. The backing method has high machining accuracy and low surface roughness. It can ensure the taper consistency of the same batch of workpieces, and can realize automatic feeding and high production efficiency. However, the manufacturing precision requirements of the backing are high. When replacing cones with different tapers, the corresponding backing needs to be replaced. It has poor versatility and is not suitable for the machining of fixed-taper cones in mass production.
The wide-blade turning method is suitable for turning short, thick cones with low precision requirements, such as tapered pins and tapered spindles. Its working principle is to use a wide-blade knife with a blade width greater than the length of the cone, grind the blade to an angle consistent with the cone’s generatrix, and turn the cone with a single lateral feed. The wide-blade turning method is simple to operate, has high processing efficiency, and a small surface roughness value, but requires good lathe rigidity and high tool grinding accuracy. It can only turn external cones and is not suitable for turning long cones and internal cones. When using the wide-blade turning method, a lower cutting speed and a smaller feed rate should be used to avoid tool vibration and ensure the quality of the processed surface. At the same time, the rake angle and clearance angle of the wide-blade knife should be reasonably selected according to the workpiece material to improve the cutting performance of the tool.
The key points of cone turning are crucial for ensuring machining quality. First, the cone must be scribed before turning to determine its length, large end diameter, and small end diameter, providing a basis for machining. Second, when rough turning the cone, sufficient finishing allowance should be left, generally 0.5-1mm. Third, the cone’s size and taper must be measured multiple times during turning, and the tool position or small slide angle must be adjusted promptly to ensure the cone’s accuracy meets the required precision. Fourth, for cones requiring higher precision, a color coating method can be used for inspection. Red lead powder is applied to the cone surface, and the cone is rotated in contact with a standard cone or plug gauge. The contact marks are used to determine the accuracy of the taper; uniform and continuous contact marks indicate acceptable taper. Fifth, when turning an internal cone, the inner hole must be machined first, and then the cone is turned using the hole as a reference to ensure coaxiality between the inner cone and the inner hole. By mastering these key points, the turning quality of cones can be effectively improved to meet different application requirements.
