View attachment 163548
Three years two months and one week, to be precise
That looks like you've made a great start, Matt -- guessing it's a JoWo #6 nib unit based on the drill letters and depths in your sketch, your section looks good. If you have an ER32 collet chuck and a full set of metric collets, you can get by without making mandrels for the most part (at least, I found that I am able to) -- just means you end up turning the parts end-for-end into a smaller collet. I used Delrin to make a holder that I could screw the cap onto (tapped the same as the pen barrel) for final sanding, and another that I could screw the barrel onto (threaded the same as the nib section). Works fine at slow speeds, even though there is some runout.
Funny thing is, I went back and found that message thread earlier today to reference it.

Yup, a JoWo #6 it is. I did give thought to skipping the mandrels - I do have a full set of metric collets. But I have a Taig Micro Lathe that was handed down to me (it was my late uncle's and my father gave it to me since he already had one and didn't see needing two) that I've only recently started to actually use, despite having it for several years now. It's fun to use it and it won't take me much to make a pair of mandrels from aluminum rod stock. I've already made a mandrel to hold the section for shaping/sanding/polishing.