Good tool setup is critical to good machining environment. While a good setup is important to all tools, it is even more important to maintain good setup of threading tools, both external and internal. Tool cutting edge has to be correctly oriented, securely mounted in the insert pocket and it has to be the right type. Its reference point, used for setup, is also very critical.

Threading tool reference point selection requires more considerations than for turning tools. Figure 38-10 shows three possibilities, in the order of programming frequency. The third version 'c' is the rarest and offers virtually no benefit to the programmer except in some cases of left hand threading. For most left hand threads, one of the first two versions is also quite sufficient.

Figure 38-10: Typical reference points for setup of threading tools

Threading insert setting as in Figure 38-10 a is the most suitable for general use and for threads that end at a shoulder. Configuration in Figure 38-10 b is suitable for threads that end in an open diameter (recess). The Figure 38-10c shows a possible setting for a left hand threading work.

Selection of tool reference point (G50 or geometry offset setting) as per illustration in Figure 38-10a is the most desirable one, when the intent is to standardize tooling setup for any type of thread. It is the most convenient setting, regardless of how a thread ends. It is also the safest...