With the help from Jacob at Tormach and some nice single point thread mills from Mari tool I have been thread milling quite a bit this last week.
One problem I have been having is that even though I am using the major diameters as referenced in the machinerys handbook, the final I.d threads I have been making are typically too tight and I have been needing to oversize my major diameters to be able to achieve a reasonable fit.
I have also use the drill sizes as specified for regular tapping.
Have others had this experience? Does one need to add a minor slop factor to get better fits when thread milling?

Thanks
Nathan