Maybe a dumb question, but now that I'm making fountain pens it occurs to me to design a combined section/housing as a single piece instead of making a custom section to house a purchased housing. The housing is just a tube with some threads, seems simple enough. A combined unit just needs to have an appropriately sized hole to friction fit the nib/feed assembly (how hard can that be?), and a threaded tenon to attach to the pen. Am I missing something obvious?
You are correct, in the same vein as a cabinet maker just attaches pieces of wood to make a coffee table.
The hole in he housing is not actually round. On some its oval and on others, it has a flat spot in it. This is because the feed is usually round, but when you add the the nib along side it, it becomes oval.
One advantage of three piece usnit, is changing nibs. I use Jowo, and offer 6 different nib widths in two platings. To change nibs to what the client wants, I just unscrew the unit and change it. A quick clean and a tune and its ready to go. I know people that actually have multiple Jowo nibs and change it out in the pen themselves whenever the mood strikes them.
You may also have a hard time getting just the feed and nib. There are guys that make there own feeds, and fit them without the housing as you suggest, but that is a whole nother level of custom. Those are the guys that make there own nibs as well.
One trick I have heard of, but I am not sure exactly how to do it. You essentially make the hole in the section, as you suggest, then use heat to soften the section and press fit the feed and nib in place. The section then deforms to fit the oval shape.
If you do give this a try, i would love to hear your progress.