Thread Milling vs Tapping Explained

Welcome back to the seventh installment of my threading series! In this article, we'll look at the pros and cons of thread milling that machinists should get to know.

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Thread milling is a modern technique for creating threads in a workpiece using a specialized cutter on CNC machines. These cutters can be made of solid carbide or have replaceable carbide tips.

The process involves a rotating tool that follows a spiral path to cut threads into the material. This method improves accuracy and allows for the creation of threads in various shapes and materials, making it a versatile and effective option for machinists.

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Thread Milling vs. Tapping: Key Differences

Thread milling and tapping are two distinct methods for creating threads, each offering different benefits and limitations.

Thread milling provides significant flexibility in terms of thread creation. With thread milling, machinists can produce threads of various diameters and specifications using the same tool. The CNC programming path for thread milling allows for precise control over tolerances and the ability to make adjustments for tool wear through CNC offsets. Moreover, because the thread milling tool’s path is programmed, it ensures consistent angular positioning, enabling machinists to perform thread cropping operations at the start of the thread to meet specific customer requirements. This control helps maintain consistency and achieve precise specifications.

On the other hand, tapping involves creating threads based on the tap's preset dimensions. As the tap wears, maintaining precise tolerances can become challenging, and there is an increased risk of sudden breakages. Tapping is generally faster, as it can create threads in a single pass, providing a quicker turnaround compared to thread milling, which may require multiple passes depending on the material.

Advantages of Thread Milling:

• Flexibility: Thread milling can produce threads of various diameters and specifications with a single tool. It allows for customizable thread depth and handles both blind and through holes.
• Versatility: One thread milling tool can create both left and right-hand threads, handle multiple thread pitches, and perform thread cropping, removing burrs and ensuring precise angular positioning.
• Surface Finish: Thread milling offers a superior surface finish by using climb milling motions and producing smaller chips, reducing the risk of leaks compared to the more aggressive tapping process.
• Small and Large Thread Diameters: Thread milling allows for precise control over cutting data and forces. This reduces the risk of small thread mills breaking in small holes, and medium-sized tools can be used effectively to create large threads.

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Disadvantages of Thread Milling:

• Speed: Thread milling may be slower than tapping due to the need for interpolation and multiple passes, which could impact turnaround time.
• Machine Requirements: Thread milling requires a CNC machine with three-axis control, which might not be available in all shops.
• Large Thread Diameters: Large threads require significant power and torque to be cut effectively, which can strain the machine and limit its capabilities.

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Final Thoughts

Understanding thread milling opens up new possibilities in machining. This article has provided insights into the mechanics, advantages, and considerations of thread milling compared to traditional tapping. Thread milling’s ability to create customized dimensions, its versatility in handling various thread types, and the elimination of certain limitations associated with taps make it a valuable technique for machinists.

In the next article, I’ll share more about “hand taps and dies” and examine their functionality, types, and crucial techniques for manually cutting threads. Until then, keep threading and stay tuned for more insights.