New YouTube video from Joe Pieczynski on cutting threads with dies under power. Probably not particularly applicable for making pens since we rarely make threads long enough to justify using power, but quite good nonetheless.
To join the thread; It may be that taper is a good thing for our purposes..... Many moons ago there was a problem with the Baron Fountain pens with them un-screwing in one's pocket. Messy! There were several suggested solutions including using a soldering iron to "mess" up the threads near the base, or applying something to the inside of the center band. This increased the friction of the threads prevented the un-screwing problem. I believe at the time the manufacturer made some minor changes to the center band.It also shows that there are two ways to eliminate that taper - either make the thread longer so that the portion that will actually be used will be straight, or else reverse the die and run the piece back through the die.