Revolutionary 1-pass thread mill for high-quality threading

Tomonori Yoda  |  OSG Corporation Applications Engineer

Work materials have evolved significantly in recent years to fulfill the changing requirement of the global manufacturing industry. Material properties have become more lightweight and resilient against strength and heat for improved functionality, durability and fuel efficiency. In order to effectively process new advanced materials, greater performance is needed from cutting tools.

For the creation of threads in a hole, tapping is the most common method, where the tool moves axially into a previously drilled hole to form threads along the hole’s wall by continuous cutting. Thread milling, in contrast, forms threads by intermittent cutting. Although OSG offers a full lineup of high-performance taps for machining difficult-to-machine materials with optimized substrate, surface treatment and tool geometry, it is often difficult to obtain suitable cutting parameters because performance is based on the tool rotation speed and a tap can only advance one pitch per revolution.

Thread mill is a tool designed to cut threads by milling. Thread mills are used on numerically controlled machining centers that have simultaneous, triaxle control and helical interpolation functions. Thread mills are applicable to a range of hole diameters rather than just one hole size like taps, where its diameter is fixed. A thread mill’s latter diameter is determined by the CNC tool path; thus, a single tool can be used to cut threads in various sizes of diameters. One thread mill alone can combine multiple operations, such as drilling, chamfering and threading.

In comparison to tapping, thread milling is more stable with less cutting condition limitations in terms of chip management and coolant lubricity. Thread mills can produce short and broken chips that are easy to manage. Moreover, thread mills do not need to be reversed at the end of the tapping operation like general taps, which minimizes the occurrence of broken tools and scrap parts. With the thread mill’s high-performance and reliability, unattended machining is also possible, making it the ultimate tooling solution for thread processing.

Why Isn’t Thread Mill Chosen More Often?

Even though thread mills are capable of achieving the best thread processing performance, there are several reasons why they are not the first tooling choice.

  1. Simultaneous 3-axis machining center is required.
  2. Machining program is difficult.
  3. It takes time to set up.
  4. Cycle time is long.

Out of all of the reasons, the long cycle time is in general the most common factor in which thread mills are not chosen.

Correlation of Deflection and Cycle Time

There is a general conception that thread milling would require two or more passes to generate a thread, which makes the processing longer than tapping. Deflection is a common problem with thread mills, because the cutting force is not balanced. Deflection and dimensional accuracy would worsen as the tool progresses toward the bottom of the hole. To correct deflection, an extra pass is used for zero cutting. If zero cutting does not resolve the deflection, more passes are required, which further extends the cycle time.

Revolutionary 1-Pass Thread Mill AT-1

To solve the problem of deflection and long cycle time, OSG has developed the AT-1, a revolutionary 1-pass thread mill for high-quality threading, withtwo patented technologies registered in Japan for its tool geometry.


1. Left-Hand Helix Geometry

The first patented technology is the AT-1’s left-hand helix geometry. As shown in figure 1, conventional right-hand helix thread mill is most vulnerable to deflection as the cutting process begins from the tip. In contrast, the AT-1’s right-hand cut and left-hand helix geometry begins the cutting process from the shank side, thereby minimizes deflection.

Figure 1.


2. Unequal Spacing & Variable Lead Flute

The second patented technology is the unequal spacing and variable lead flute geometry, which is commonly applied in end mills. The unequal spacing and variable lead flute geometry minimizes vibration. Even though the amount of cut has increased with one pass cutting, superior and consistent surface finish can be achieved as illustrated in figure 2.

Applying the unequal spacing and variable lead flute geometry in thread mills involves a high degree of difficulty because the thread pitch has to been adjusted accordingly to the flute geometry, which requires special manufacturing techniques.

Figure 2.


Although thread milling is a more mature cutting process, it can outperform conventional tapping with increased reliability, surface finish and accuracy. With the AT-1’s capability to generate threads in one pass, it is the ultimate thread milling solution for difficult-to-machine materials like stainless steel.