Gary, typically there would not be any need to remove any material, the manufacture/designer will have set the proper thrust into the nose of the plane. However when using the contra drive the thrust in the nose will need some adjusting and adding material would be the easiest way to do that, a tapered ring can be glued to the nose to set the zero right and .5 down thrust. The Spark (older version) is a special case because the plane uses a 64 mm spinner but the contra drive is 82 mm. In this case I set up a marking jig with the proper thrust on the nose, marked where to cut and then cut/sanded to the mark. At this point the nose was not completely round so I added a forming ring about 3/16” behind the cut line and used ca to glue in place. This ring was temporary so I used a glass/foam composite material that would be easy to sand/remove later after the main fuse ring was installed, this ended up being about 1/2” behind the cut line. I have attached several pictures of the high precision equipment and the set up used to give the plane the nose job. Hope this helps but again this was a special case and adding material would be my normal choice not cutting up an expensive fuse.

Dave