For a larger view click the pictures.
The first two pictures show how Jim used a long threaded shaft and two tapered end pieces to make a jamb chuck. This gave him easy power sanding of the exterior. Similar to how you sand a lathe project.
The picture above shows how Jim mounted a flap sander to the shaft. The flap sander on the long shaft gave him easy reach into the hallow mug.
The last two pictures show a third use of the jig. This made sanding the interior of the mug fast and easy compared to hand sanding. I don't have all the construction details of the jig but with a little effort you could easily make something similar. If you plan to make several of the mugs to sell this jig would make you much more efficient.
Thanks for taking the time to share these tip with us Jim.