The entry of the threading tool into the material can be programmed in several ways. One of the most important options is the method that controls threading tool approach towards the thread, also known as the threading infeed. This is a method detailing the motions of the threading tool, using one of two basic methods of infeed, as illustrated in Figure 38-10.

Figure 38-10: Radial and Compound infeed for thread cutting

One common infeed method in thread programming is the plunge method, sometimes called the radial method, also known as the straight or perpendicular infeed; the other method is called an angular method, better known as a compound infeed or a flank infeed.

The need to control the infeed direction in threading is to offer the best cutting conditions for the insert edge. Except for threads with very fine leads and some soft metals, the majority of threading cuts will benefit from a compound infeed (at an angle). Some threaded shapes are excluded for the reason of their geometry - for example, a square thread will always need a plunge infeed (straight radial infeed). The angle of infeed is programmed with the A parameter of the G76 cycle.

Each threading method has its own procedures, using the following features:

• Constant cutting amount

• Constant cutting depth

• One edge cutting

• Both edges cutting

The P parameter of the G76 cycle selects the feature.