This is the latest version of a sanding mill I made to be used after the pen barrel is turned and finished. The platen is a washer epoxied to a backup collar held to the shaft by a set screw.
I now find it works just fine held in my hand (second picture) with my fingers lightly holding the disc of sandpaper. The sandpaper is not glued to the sanding platen of the sanding mill. No need.
Here you see a pen barrel already turned (you have to imagine that it is finished also
) and ready to have the end sanded square. Again, I do not use a drill chuck as pictured; I just hold the mill and the piece of sandpaper with my left hand and twist the pen/tube with my right hand.
Even if there is a good glob of CA on the end of the pen I find it sands right down in just a few seconds by twisting the barrel by hand. Since the sandpaper is not glued down it is very simple to change to another grit if needed.
This concept is almost identical in principle to that shown by VisExp above - mine is metal and his is wood. My mandrel shaft is a snug fit to a 7mm tube. Sleeves just like his are used for larger diameter tubes. Another member is selling an all metal one piece sanding mill turned from a single piece of steel. Check that out over in the classified forum.
Since the sanding mandrel shaft and the platen are an accurate 90 degrees to each other (accuracy of the drilled hole) there is no need for any alignment adjustment as with some jigs - the pen barrel will always be at 90 deg. to the platen, and thus to the sandpaper.
I am working on a similar sanding mill design incorporating the 6 blade cutter head just received from the group buy. I am hoping to eliminate the need for adapter sleeves.