Is it better to machine threads by milling or tapping?

What is the difference between using a tap and a thread mill in threading?

When threading a hole on a standard milling machine, the tap uses only the machine's Z axis to cut. A thread mill will use all three axes to cut the threads and use circular interpolation cycles to give the operator greater control.

What are taps and thread mills?

Both replaceable and solid thread mills can be made from carbide. Taps are available in a variety of materials, such as high-speed steel, powdered metal, and sometimes carbide.

Only one material is needed for thread milling tools because the circular interpolation method reduces the load. This creates side forces on the tool.

Taps are available in a variety of materials, mainly because the machine load is forced to be transmitted through the Z axis. This means that carbide taps are often too unstable, so a better material is needed.

Why is thread milling safer than thread tapping?

With thread tapping, the operator has no control over the cutting process. Usually a G84 threading cycle is used, and it cannot be stopped midway until the tapping cycle is completed. With thread milling, the process can be more controlled.

Due to high loads, difficult chip evacuation, or poor hole conditions, the thread cutter may break in the hole when tapping, resulting in the workpiece being scrapped. Or at least the thread cutter needs to be machined and removed by electrical discharge machining (EDM). Thread milling is a safer and more stable process and is definitely the preferred method for unmanned operations (green light machining) or expensive workpieces.

Large Diameter Thread Milling vs. Thread Tapping

When we start discussing holes over 20mm, we usually talk about how the machine tool drives the thread cutter. For holes of this size, using thread tapping can become very expensive. Thread milling not only reduces the cost per hole, but also reduces the chance of large thread cutters breaking.

Because thread mills generate very low cutting forces, they also greatly reduce the load on the machine tool compared to thread tapping.

Which is easier, thread milling or tapping?

When machining small diameter holes, both thread milling and tapping produce threaded holes well without any damage to the machine. But when we talk about larger holes, the tapping forces increase dramatically. Thread milling, on the other hand, keeps the loads low regardless of the thread size.

Thread milling vs. tapping?

In almost all cases, thread milling is more efficient and less loaded than tapping. You can use multi-pass strategies with thread milling. If you want to reduce the cost per hole, thread milling is usually the preferred solution.

What is the difference between re-tapping with a thread mill and tapping?

Re-tapping with a thread mill is easy if the part is still on the machine. The operator will adjust its offset compensation and restart the cycle. There is no danger of cross-tapping or damaging the part. In almost all cases, threads produced with taps must be re-tapped manually with additional taps.

Precision Advantages of Thread Mills

Thread mills can produce more accurate holes. With 100% control over the diameter, the machine load is stable and the chip removal is more thorough, which improves the surface quality. In contrast, when using the same size tap, the operator cannot control the discharge process of the chips through the spiral groove.

Applicability of difficult-to-machine materials

Thread mills perform better when machining complex materials such as titanium, hardened steel, and nickel alloys. Taps are prone to breakage due to increased cutting forces, while thread mills can reduce cutting forces by adjusting cutting strategies, resulting in more consistent and high-quality threads.

Efficiency Comparison

Taps are usually faster because they only rely on the power of a single axis of the machine tool. However, thread mills have more advantages when machining small-diameter threads: taps are prone to jamming due to their small diameter and high load, resulting in scrapped workpieces; thread mills have lower cutting forces and better controllability.

Reliability of deep hole processing

For deep hole threads (such as 3 times the hole diameter depth), the thread milling cutter can process to the bottom of the blind hole without a spiral structure, and can control the long thread processing process by adjusting the strategy to avoid the risk of taps breaking due to repeated use, ensuring processing safety and quality.

Processing after tool breakage

If the thread milling cutter breaks, only a new tool needs to be replaced to continue processing; while the workpiece may be scrapped after the tap breaks, and re-drilling and tapping are required.

Summary: Thread milling cutters perform better in precision, adaptability to difficult-to-process materials and deep hole processing, while taps have advantages in efficiency, but tools need to be selected according to specific scenarios.

Thread Milling vs. Tapping How do you produce higher quality threads?

The thread milling process is superior to tapping. It produces a smoother surface finish and a better visible thread quality.

When should you switch to a tap instead of a thread mill?

In most cases, a thread mill is the better choice as it provides longer tool life and better control over the thread and surface quality. However, sometimes factors such as cost come into play, meaning it may not be the right choice. Thread mills are more expensive than taps of the same size, and some processes may also require additional costs, especially when processing small batch orders and profit margins are tight.

When should you switch to a thread mill instead of a machine tap?

Unlike taps of a specific size, thread mills are able to produce a wide range of threads. One pitch can be used for multiple diameters, and threads finer than the larger diameter can be produced by simply adjusting the thread diameter, saving the cost of purchasing multiple different tap sizes.