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Surface Finish - Depth of Cut
Imagine a tool tip with small angle coming to a sharp point. It is cutting in the -Z direction along the surface of a rotating work piece. If the tool is making a very shallow cut, so that the width of the cut is less than 1/72mm, the ridges between the shallow grooves will have flat tops. If the depth of cut is such that its width is exactly 1/72mm, the ridges between these deeper grooves will have pointed tops. Either way, the workpiece will end up over-size as only the bottoms of the grooves are at the correct diameter.
In reality, tool tips are not narrow and sharp pointed. They have a large included angle and a tip radius. These, together with a feed rate appropriate to the spindle speed, which itself should be appropriate to the material and its diameter, help to make cuts at successive steps overlap and produce a good finish. Even so, the step effect is visible to the naked eye and very obvious under a magnifying glass. But, as long as the finish is good enough for the intended purpose, the steps do not matter.
Tapers and curves will also appear stepped. They are a miniature version of the jagged outlines of bit map graphics when magnified on a computer screen. However, WELturn does smooth things out a bit. When the tool has to move one step in X followed by one step in Z (or vice versa), it moves both axes simultaneously so that the tool tip moves at 45 degrees and cuts off the corner of the step. This means that the finish on a 45 degree taper is as good as a surfacing or facing finish.
Finishing Cut Directions
Feed Rates
Speeds and Feeds for Turning and Parting with Indexable Tipped Tools
Surface Finish - Feed Rate