Thank you to all for sharing your experience with great input and comments. You helped me find what I could not find on my own through web searches.
Lacking a better web search, I started down the Pentel path independently. I didn't realize that I was re-inventing the wheel. I have known and used Pentel P205 0.5 mm pencils for decades. I went to the art supply store and looked at a lot of mechanical pencils, concluding that the ONLY one that might work is the Pentel P205 type. The others all had threads and other protrusions in the tube that were an integral part of the retention and/or operating mechanisms.
I took measurements of a Pentel P205 mechanism with a caliper. A couple days ago I bought small brass washers. I felt that wood might not provide a sufficiently strong, firm seat for such tiny "wings" in the mechanism. I like the small outer diameter of the washers, which should fit easily inside a wood pencil tube, but I'll have to enlarge the inner holes slightly. I will make a small drill hole jig to hold the washers while I use twist drills to enlarge the inside diameter. We'll see. I may have to find smaller washers.
Continuing my plan, I will drill a pen blank with the small exit hole for the part where the screw threads on the nib attach, then again with a stopped hole for the mechanism. I'll turn the wood between centers, glue the washer in the base of the mechanism hole, assemble it, and PRESTO! - I'll learn what doesn't work and needs to be fixed or altered. I will figure out a different clip solution, if any. I like thin pens, but don't need these pencils to match the Pentel outside exactly. Besides, the Pentel clips are ugly.
In case anyone can use them, here are my incomplete measurements:
Hole size for pencil tip threads: 3.95 mm
Hexagonal seat size between flats: also 3.95 mm
Hexagonal seat size between corners: 4.45 mm
Basically the pencil mechanism relies on the 0.25 mm angled "wings" at each hexagonal corner to seat. (4.45 - 3.95 mm) / 2 = 0.25 mm. The wings are not fully supported, either. The total cross sectional support area seems very small to me, and I wonder if even very dense hardwoods are strong enough to hold that lip through heavy use. That's why I thought of using brass washers as a seat for the mechanism. We'll see.
I don't have the rest of the measurements yet. If I succeed, I'll post instructions on how to duplicate my work.
I know what I like in 0.3 mm and 0.5 mm pencils, but I want to make them in nice wood versions. There is an indescribable quality to wood pens and pencils that cannot be replicated with ordinary commercial products. That includes pride in workmanship. It may be nothing more than self-indulgent vanity, but I like to think that it is worth the effort anyway.
In the meantime, I have already looked at the links and instructions that you posted above. Thanks again and please keep them coming. I plan to make a few of the recommended kits, too.
