Looking at your file, clearing tangential extension value removes cutting air on first pass and clean up pass at the end.
This results in only cutting stock and only cutting uncut area such as undercut on short side of shaft.
Changing depth of cut will result in either undercut being last pass or undercut being included in last pass starting from face.
Now, the usefulness of air pass is debatable, one air pass may be useful in castings and forgings where shape and size varies but I would not opt for this for two reasons.
First, if stock is inconsistent, interrupted cut and shallow / deep fluctuation would more likely result in destroying insert tip before tool reaches end of first pass.
Second, air pass over long shaft or large diameter is waste of cycle time.
I prefer to make one pass over inconsistent stock by making one pass below lowest point, but at slower feed rate to prevent tool from chipping when it goes over thicker stock.
Slow feed will produce strings so pecking takes care of that, once stock is uniform in size and top surface is removed, I can step up feed rate and rough rest of the stock with same conditions.
Last pass being significantly shallower then all other passes will likely produce strings, the hairball gets wrapped around tool and then driven into the shoulder while cutting undercut at the same time,............ not good.
I will agree that there are times when this could be beneficial but in most cases it is not.
In G71 and G72 cycles, cleanup pass is done by default and it can be a challenge to avoid strings on last pass as breaking chips is relative to depth of cut, spindle speed, feed rate, insert style and material type.
So CAM generated code that avoids last, shallow pass is preferable.
Fusion
