Daniel,
If you are using a sharp SHARP V tool, then DEPTH=.86603 X Pitch, assuming it's positioned
on the OD of the material. You also account for actual outside diameter and any tip radius of
the sharp v tool if setting to an outside turned diameter. There are tolerances on the major, minor and pitch diameter. If not the, the pitch diameter may not be in tolerence post cutting.
If the threading tool is not ground to the correct angle, then thread form will not be correct.
And good grief when you start looking at all the different standards.
The I determines how the thread will be cut, such that at 30 it would be radial infeed. As you change that
down ( i use 15 on the small lathe to get an even removal of material per pass which provides for a more consistant
spindle speed and cutting, when required) and then you end up with a flank feed.The flank feed is based on a formula which shifts the z based on pass depth of each individual cut to accomplish even removal of material.You can see effect by generating a G32 code.
RICH