How do you machine a job with a non-monotonic variation in surface profile, i.e., with radial or axial undercuts, if Type II G71 / G72 cycles are not available? May use a CAM software if you have access to it. That is perfectly okay. But, how do you machine a workpiece obtained by casting or forging with only slightly oversized dimensions, say, about 2 mm? One cannot use G70 because removing 2-3 mm material in one pass may not be permissible. G71 or G72 would be too inefficient because the tool would cut in air most of the time. One can, of course, use a CAM software where the initial shape may be appropriately defined, but that also requires additional modeling time as well as software expertise. G73, on the other hand, can very quickly machine it to the final size in just a few passes (depending on the chosen depth of cut in one pass and the amount of over-size). G73 is designed mainly for such applications only. Read on and find out yourself. Manual part programming would never be the same again!