I will show first pen.
I have used mandrel and bushings that comes with lathe.
Mandrel was slightly curved and bushing diameter was 0,5mm more, then needed for slimline.
So, pen is not round, and been made wood-to-bushing, but not wood-to-nib.
Also, with lathe comes blanks (rounden and with glued tubes), but not from single piece of wood!