Mach monitors the spindle rpm. The spindle needs to have adequate spindle torque to be able to cut the thread. Changes in spindle rpm while
cutting can cause problems, Mach alters the feed rate based on rpm but can only do so much to fix the thread. I talk about this in the write up.
One should know by trial / testing of cutting threads what their lathe can do. For smaller lathes a different type of cutting method ie; alternate flank
and pass depth settings should be used to assist in cutting deeper thread depths.
Initial od of the stock, proper total depth of cut, accounting for tip radius etc. will go a long way to achieve proper thread pitch and pitch diameter.
Your threads will only be a accurate as your lathe. Be meticulous in setting up for threading as in some cases just a small change in pitch diameter
is an out of spec thread.
All of the above is in the write up.
If your the "the nut goes on" type of machinists and happy so be it, but, there are reasons for thread spec tolerances.
Have fun,
RICH