I had a mandrel made about seven years ago to aid in turning Pentel pencil conversions. I have made countless pencils with it to date and will continue. Here is a photo of the mandrel.
It uses two 1/4 x 28 nuts and a slimline size bushing on one end and two 8-32 nuts with a shop made bushing on the other end. Here are additional photos of the mandrel with a blank mounted and another picture of the setup mounted on a lathe.
This setup makes it easy to turn the Pentel pencil conversion.
Chuckie