Getting the parts out is easy -- just unscrew the nib and everything slides out the the opposite end.
Measure the length of the mechanism minus how much you want to expose of the advance button. You'll also want to subtract enough length for thread exposure to reattach the nib. That should add up to about 4.25 inches or a smidge longer. Your total blank length will be about 4.5 inches. Use a 1/4 inch drill bit to drill the 4.25 inches. Now comes the tricky part -- drilling the rest of the way through the blank. You'll need a 5/32 inch hole centered on the 1/4 inch hole.
What I did: Used a 1/4 inch aluminum rod (which I had lying about), chucked that up in the lathe (using the pin chuck), and drilled a 5/32 inch hole in the center of the rod. Then I CA glued the same size drill bit in that hole (sharp end out, of course). That gave me a 5/32 drill bit about 7 inches long -- a home-made step drill. You won't find that item in your local big-box store.
Slide the newly made step drill into the partially drilled blank. The rod should be a nice snug fit which will center the 5/32 bit where it needs to be. Use your three-jaw drill chuck in the headstock and you can probably hand drill that remaining 1/4 inch of material through the end of the blank. You may need to adjust this short length on the nib end. After the nib is screwed on that small step is what actually holds the guts of the pencil in place. It needs to be long enough to allow 4-5 threads to be exposed so you can actually screw the nib on.
Now you can turn between centers to your desired profile. You might want to stabilize the ends of the blank with a little thin CA glue to help minimize the problem of splitting the blank from tailstock pressure.
This particular piece actually snapped in two in the polishing process. It was a fairly clean break so I just glued it back together -- can you find the weld? Working without a brass tube leaves a pretty thin and potentially fragile little twig. If you want you can drill to 7mm and use a tube. Same basic process but you'll need to adjust your step drill size appropriately for the ID of the brass.
Use your parting tool to create a shallow groove for the clip. For this clip that required an OD of about .375 inches -- so your blank obviously needs to be a bit larger than that. I think this one was about .420 in that area. You'll also want to protect your blank from being scratched as you slide on the clip. I slipped the clip onto the butt end of an appropriately sized transfer punch, wrapped the blank in a single layer of paper towel, and the clip slipped right down without a mark. Rotating the clip around released the paper from under the clip.
Then just slip it all together, screw on the nib and voila, you've got a customized pencil. :biggrin: Have fun.