Indexable vs. Solid Carbide Thread Mills

[Geoffrey Less]

When milling threads (as opposed to using a tap and die), machinists often have the option of using either indexable or solid carbide thread mills to complete the job. The best choice will be determined by the unique needs of the application with respect to the flexibility of the tool and the quality of the threads it can produce.

Here’s what you need to know.

Solid Carbide Thread Mills (and Where You Can Get Them)
Due to their exceptional hardness and wear resistance, solid carbide thread mills can be run at high speeds. This means they can cut quickly and efficiently. Often, solid carbide mills feature more flutes than indexable thread mills, yielding a greater penetration rate, too.

Solid carbide mills also feature smaller cutting tool diameters than indexable mills, which results in less overall contact between the workpiece and the mill; this generates less heat and deflection, which improves the quality of the finished piece.

Thread quality may also be affected by the fact that carbide mills grind threads simultaneously, improving consistency and finish.

Due to these advantages, some machinists prefer to use solid carbide mills, such as those sold by Online Carbide (OnlineCarbide.com), which are made in America and offered at low prices.

However, indexable thread mills are not without their advantages.

Indexable Thread Mills
The main advantage of indexable thread mills has to do with the fact that they accept inserts that enable the user to change out thread forms easily and quickly. This enables efficient, fast cutting of multiple different threads, with respect to pitch or form.

This gives indexable mills a decided advantage over solid carbide thread mills in terms of flexibility. With an indexable mill, you only need to buy the body; then several different forms for cutting different threads. This can be more practical than maintaining a set of solid carbide mills.

It is also notably more cost-effective. While solid carbide thread mills (and other solid carbide mills) are preferred for performance and speed, indexable thread mills are often substantially more affordable.

On the Advantages of Thread Milling
Regardless of whether the performance of solid carbide mills or the cost-efficiency of indexable thread mills is for you, milling has many advantages over tap-and-die thread cutting.

First, milling is more flexible than cutting with a tap and die. Milling can be used to cut both left and right threads, as well as threads of differing pitch. One tap can only cut threads of one specific hand orientation and pitch.

Thread milling also delivers superior chip evacuation and can be done more quickly and efficiently than with a tap and die, resulting in a superior finish and higher-quality threads.

Milling can also be performed on materials that are difficult to cut with a tap and die, such as hardened steel. Moreover, milling can produce complete thread profiles from the top of the hole to the bottom, eliminating the need to drill deeper than necessary to complete threading with a tap and die.

No matter how you look at it, there are substantial advantages to milling threads, whether you use carbide or indexable thread mills.