Nose Cone Shoulder Edges TIP

From a correspondence with Neil W:

"Bonus note: I also found out, by accident, that a body tube with the edge coated with CA and not smoothed down with sandpaper makes a highly effect balsa sander... I haven't tried to exploit that intentionally yet though. "

My answer:
I do this, but rough up the body tube end with 220 grit. 

Insert the nose cone (here an adapter) and turn to sharpen up the shoulder. The rough end of the tube "sands" and squares up the shoulder edge.
On the left is the before, you can see the rounded shoulder edge. On the right the edge is sharper after the tube edge "Sand".

After that, I'll smooth the tube end with 400 grit, then a wipe of CA glue, maybe 3/16" in and around the edge. That gets polished off with 800 grit.