For a late birthday present, I got a Rotring 600 0.5mm mechanical pencil. It’s a great pencil, but the tip does not retract, making it very un-pocket-friendly. I set out to make a lid for it, and after exploring wood, acetal, UHMW, and teflon, I opted to go with polycarbonate (partly because I found it for cheaper than the others). First, I measured it with a dial caliper, and then selected drill bits and depths from there.
After building a proof-of-concept model with a wood dowel, I used my Grizzly 7×12 lathe with center drills and four regular bits (smallest/deepest first) to build one with 7/16″ polycarbonate rod. I cracked the first attempt, broke off a drill bit in the second, and while the third is not perfect, it works. Apparently, polycarbonate turns to powder when overheated — not good, but good to know.
Thanks to the slight taper on the grip, the cap as built fits snugly, keeping the tip out of harm’s way. Now the pencil is pocket friendly, can be carried or stored with the lead out, and as long as I don’t drop it on the tip while using it (granted, this is when it is most likely to be dropped), I should be good to go! As an added bonus, the cap is apparently compatible with the Alvin Draft/Matic series; I bought an 0.3mm pencil ( No. DM03 ) as a more-affordable complement to the Rotring, and its grip has similar dimensions.