Heres a pic of my homemade 7mm pin chuck, made from my dwindling supply of brass scrap. Turned on my wood lathe with a file and recess for pin then cut with a router. The pin is just a bit of welding rod. The hardest part of making one of these is finding the pin every time you drop it on the floor. As the photo shows, I now use an old bit of 7mm tube to keep it together during storage.
I am also toying with the idea of taking my mandrel to a machine shop and asking them to grind a flat surface on the non threaded end of the rod. That way, I can just turn the rod around in the mandrel for closed ended pens.
I am also toying with the idea of taking my mandrel to a machine shop and asking them to grind a flat surface on the non threaded end of the rod. That way, I can just turn the rod around in the mandrel for closed ended pens.