OK, so they aren't objects of beauty. What they are is leftover scraps of UHMW polyethylene that I scavenged from work. The polyethylene has two qualities that make it perfect for this application. One is that it machines easily (it can even be worked with a hand plane). The other, more important property is that the acrylic doesn't stick to it. I tried using ABS pipe but the acrylic bonded to that so hard it might as well have been one solid piece.
After screwing 2 pieces together I took them to the drill press and drilled a 5/8" hole a little deeper than the length of the brass tubes of the pen. Then I drilled a 1/4" hole in the bottom of the first hole that went almost through the block.
Next I took another piece of the UHMW over to the lathe and turned it down until it would just slide into the brass pen tube. I left a small step at the bottom so the brass tube wouldn't go all the way to the bottom and a small flange to keep the rod from going too far into the hole. The bottom of the rod was turned to 1/4" to fit snugly in the hole at the bottom of the mold.
Here are the brass tubes slid over the rods.
This picture sort of shows you how the rod fits in the mold.
The assembled mold , with the brass tube inside.
About ten minutes later, give or take, depending on the room temperature, you can split the mold apart.
Sliding the blank off the pins may or may not be easy, depending on your timing. Most of the time though it's pretty easy. Once you do that you just need to square up the ends and the blanks are ready to turn.
The new pen molds are a big improvement over the old ones. The blank is a lot closer to round and there is less waste. It's easier to get the blank out of the mold as well, which was the main objective. There is still room for improvement, though. The pins, for instance, need some refinement. One day there will be a Version III (the roman numerals make it fancier).