Six Reasons Thread Milling is Better Than Tapping

By Bob Winegard, Application Support and Training

Thread milling surfaced approximately 25 years ago in response to NASA’s need to machine high-quality threaded holes in extremely tough materials such as titanium, Hastelloy and Inconel – a feat not possible with a tap. Over the years, thread milling has and continues to evolve, and manufacturers are now using the process to produce strong, exceptional threads in hardened materials up to 70 Rockwell.

Top six reasons thread milling is better than tapping:

1.  You’ll always achieve a better thread quality with thread milling than tapping.

2.   Depending on your hole size, you can perform tapping either by hand or machine. With thread milling, however, you must always use a machine, which ensures better overall thread consistency. 

3.  Thread milling is a lot easier on your machine tool because it requires much lower cutting forces than tapping.

4. In thread milling, you don’t have to have the hole right on size because the thread mill will cut the hole larger. When people tap, they typically tap the hole larger than necessary because it is easier. However, in doing so, they lose part of the thread and reduce its overall strength.

5. It’s common for smaller taps to break during the tapping process. Upon breaking, you can try to get the tap out of the hole, which can be time consuming, but more often than not, you will need to scrap your part.    

6.  With thread mills, you can create right and left-handed threads using the same tooling.

Keep in mind, however, before you can thread mill you must have a machine tool with three-axis capabilities. While most of today’s machines have such abilities, a lot of older equipment does not. You must also consider how deep you need to thread mill because you should not go deeper than one and a half times the diameter of your hole. The reason being is that the longer your milling tool, the more chance you have of experiencing deflection, which can create inaccuracies in the thread.

With thread milling, you have a couple of tooling options from which to choose. You can opt for either a solid carbide or indexable tool. Solid carbide tools are ideal for smaller hole sizes because an indexable tool typically won’t fit in holes that are ⅝” or less in diameter. In terms of cost, solid carbide thread mills are more expensive than indexable designs. With an indexable tool, once you've purchased the thread mill body, the cost of the inserts are more affordable than solid tooling. Indexable tools also have shanks made of steel, which makes them more forgiving than solid carbide tools.     

Lastly, before you go to thread mill, be sure to take advantage of Seco’s Thread Milling Wizard software, which is available via our web site. The software will ask you a series of questions about the type of thread you’re trying to achieve, and based on your responses, it will create a highly effective, tailor-made CNC program for use with your machine tool.

About the Author  

As an integral member of Seco’s dedicated application support and training team, Bob works closely with Seco customers to help them optimize their tool usage and find ways to increase their productivity and reduce costs. Contact Bob at bwinegard@secotools.com.