What’s the Difference Between Thread Milling and Tapping? 

Compared with tapping, which process should you choose? Tapping is usually used to make threads in small holes after drilling, while thread milling tends to produce threads in larger holes. Tapping uses a tool of the same size as the thread, forcing the chip through the thread to evacuate, while thread milling uses a tool with a smaller size than the thread, so thread milling achieves a better thread quality than tapping. 

Tapping can be performed either by hand or machine. Thread milling usually requires CNC machine tools with at least three axes for helical interpolation. Thread milling requires lower cutting forces than tapping. It is not necessary to have the correct hole size in the thread milling process, a single tool can be used in thread milling to make a wide range of hole sizes. While for tapping, a different size tap is required for each size hole that needs to be threaded. Thread milling produces pipe threads easily without creating the troublesome stringy chips produced in the tapping process. Thread milling can achieve a better thread quality and smoother surface than tapping Thread milling gives the user the ability to design custom threads, while the custom taps can be very expensive and require long lead times. 

Tapping does not allow for adjusting the thread fit. Once the hole is tapped, the size and position of the thread are fixed. While the thread milling can control the fit. The machine operator has the ability to adjust thread size using a strategy similar to using an end mill, rather than a drill bit to make a hole.