Keeping Fin Edges Square TIP

When sanding filler, primer or wet sanding between color coats you don't want to round over purposely squared fin edges.
On this Payloader II model the leading edges are rounded, all other sides are square.

On the right I'm sanding the flat sides of the fin right up to the squared edge.
Notice I make a "V" with my thumb and middle finger. With the sandpaper wrapped over my thumb it keeps it from getting too close or going over and rounding the square edge.
By varying the pressure and position you can get very close to the edge.

To sand the outside square edges, use sandpaper wrapped around a Q-tip.
Hold the fin under a bright light so you can see the gloss shine of the paint on the flat edge.
Just sand enough to dull the paint gloss.

Follow up with another undercoat.