When I first began to turn pens in 1997 I discovered something about the Parker Senior Duofold that surprised me. I needed a set of taps and dies with which to make replica pens, after which I would add original vintage medal parts (nibs, filler button, pocket clip, and pressure bar) for a complete pen. I took three or four vintage Parker Sr. Duofolds to a Machine Gauge Shop so that I could obtain the exact size the new set of taps and dies should be. To my surprise the shop owner informed me that only two of the pens were alike in thread dimensions. When I ask , "how could that be", he set me down and explained the process of part duplication. He farther explained that two of the four pens would not have passed the "go or no go" test in a modern machine shop. They were too far out of size restraints for modern part run production. His question to me was, "which pen do you want me to use as a gauge for your new set of taps and dies?" Needless to say, I was dumb founded! With his counsel the decision was made to make my set of taps and dies the size of the two pens that were alike. Over the years I discovered that decision to be my first $1,000.00 mistake. All though my set of T&D's were very usable, the parts I turned such as the cap inner cap were too loose to be perfect for replacement on most vintage pen caps and the sections that I turned were too tight to be used for replacement of most vintage sections. Either of the parts could be "chased" and made to work but they were not perfect.
Early on I came to an educated conclusion. Parker pen company probably had at least three different production lines turning parts for the Parker Sr. Duofold during the height of their production of this specific pen. Here is why I have come to that conclusion. It was common practice long ago for machinist to make their own tooling. Because they did not have the advantage of Computer Numeric Controls (CNC) they very easily could have varied just the slightest bit in the tooling that they made. Thus the slight variations in the size of parts they produced. Were this the case each production line would have produced pens that varied a few thousands from those produced over in the other line. If my guess were to be correct, the reason why the four pens I took to the gauge shop varied in size, makes since. Another explanation might be that the different production lines used separate gauges to determine when it was time to change used tools.
This subject may not be of interest to most, but it is just a little insight into what happens in the machine shop when one is faced with turning parts that must or should be exactly alike every time. Ole machine shops were very good at setting their machines up with correct stops but it would be near impossible to be 100 per cent correct every time. The modern CNC shop has made many improvement over the years. However, anytime one introduces humans into the scenario perfection goes out the door.
Now that I have had the experience of turning several thousand pens using a conventional lathe, I have come to the conclusion that the learning curve is a long one.
Thank God that mankind built servo motors! I just wish I could afford three computer assisted machines: A lathe, a mill, and a laser engraver. I could really get into the pen business.