The cutting cone angle of a pipe thread tap is one of the core parameters in tool design, directly affecting force distribution, tool life, and machining quality during the cutting process. As a specialized tool for machining internal threads in pipe connections, the cutting cone angle of a pipe thread tap needs to be specifically designed based on material properties, thread type, and machining scenario to balance cutting force and machining efficiency.
The impact of the cutting cone angle on cutting force is primarily reflected in the contact area of the cutting edge. A larger cutting cone angle shortens the effective length of the cutting edge, significantly increasing the cutting load per unit area. When machining high-hardness materials, this design may lead to tool breakage or fracture due to localized stress concentration. For example, when tapping tough materials such as stainless steel or alloy steel, an excessively large cutting cone angle will intensify friction between the cutting edge and the workpiece, generating high temperatures and accelerating tool wear, while also increasing cutting force and even causing vibration, affecting thread accuracy.
Conversely, a smaller cutting cone angle can extend the cutting edge length, distribute the cutting load, and reduce the pressure per unit area. This design is particularly effective when machining brittle materials (such as cast iron), effectively reducing cutting impact and preventing material breakage. However, an excessively small taper angle leads to an excessively long cutting section, weakening the tool's rigidity. This is especially problematic when machining deep hole threads, potentially causing thread misalignment or excessive surface roughness due to insufficient guidance. Furthermore, a small taper angle increases chip removal difficulty, making chips prone to clogging in the chip flutes, further increasing cutting forces and creating a vicious cycle.
The selection of the cutting taper angle also needs to consider the thread type and machining scenario. For example, tapered pipe thread taps, to ensure sealing, typically use a 1:16 taper design. Their cutting taper angle must match the thread taper to ensure uniform cutting force distribution during machining and avoid localized overload. Cylindrical pipe thread taps, on the other hand, prioritize cutting smoothness, requiring a cutting taper angle design that balances chip removal efficiency and tool strength. When machining through holes, right-hand helical flute taps use their helix angle design to expel chips upwards. In this case, the cutting taper angle needs to be optimized in conjunction with the helix angle to reduce cutting force fluctuations. Blind hole machining requires a larger cutting taper angle and a shorter cutting edge length to prevent chip accumulation at the bottom of the hole.
Material properties are another key factor in cutting taper angle design. When machining steel, a cutting cone angle of approximately 30° is recommended to balance cutting forces and chip removal efficiency. For brittle materials such as cast iron, a small cone angle of 6° to 10° is suitable, utilizing its low cutting force characteristics to reduce the risk of material breakage. For high-strength or high-temperature alloys, the cutting cone angle needs further optimization by increasing the rake angle or adopting a segmented cutting edge design to reduce cutting forces and improve tool life.
The cutting cone angle is also closely related to tool life. While a larger cone angle will increase cutting forces, tool rigidity can be improved by reducing the cutting edge length, making it suitable for short cutting strokes or intermittent machining scenarios. A small cone angle, due to its longer cutting edge, is more suitable for continuous cutting or mass production, but the lack of rigidity needs to be compensated for by strengthening the tool material (e.g., using a cemented carbide substrate) or surface coating (e.g., TiN, TiAlN).
In practical applications, the selection of the cutting cone angle must be combined with the machining equipment and process parameters. On CNC machine tools or automated production lines, the force changes caused by the cutting cone angle can be compensated by adjusting the spindle speed and feed rate. When tapping manually, a medium cone angle design should be prioritized to reduce operational difficulty and the risk of cone breakage. Furthermore, the use of cutting fluid can significantly affect cutting forces; by reducing friction and heat accumulation through lubrication and cooling, it allows for a larger design margin for the cutting cone angle.
