The control systems can perform many internal calculations and store their results in the control memory for further use. This feature is especially useful for threading, since the repetitiveness of block-by-block tool motion can be avoided and the program shortened significantly.

We will use the same program example that illustrated the G32 command and apply it to a simple threading cycle. This cycle is usually called the G92 threading cycle on Fanuc controls. Incidentally, G92 in the threading context has nothing to do with the command of the same name, the traditional and now old-fashioned G92, the position register setting command. If the lathe control uses G92 for simple threading cycle, use G50 for the position register command. This applies for older controls only, since modern controls use advanced geometry offsets.

The schematic illustration of a G92 thread cutting cycle is shown in Figure 38-8.

Figure 38-8: G92-simple thread cutting cycle

For a comparison with the G32 programming method, the same thread will be programmed, 12 threads per inch on a 3.000 inch external diameter. The program will do exactly the same job, except it will have a noticeably different structure.

Using the G92 cycle, the following list shows the calculated diameters for each thread pass, as they will appear in the program (no change at this stage):

Pass #1 depth =  2.9720Pass #2 depth =  2.9520Pass #3 depth =  2.9360Pass #4 depth =  2.9230Pass #5 depth =  2.9130Pass #6 depth =  2.9040Pass...