Chris I did it as in your photo
I am ordering some sets of taps from Ausee,, I believe they are the same as you get from Arceuro Trade.
Had another look this morning at the thread, very shallow, I will see how it goes, I can always cut it off and start again.
This is the first time I used a mill so all a learning experience.
What is metal working oil, Google is giving me conflicting views.