On page 16-02, step 6 indicates to remove some material where I/O skins are mating on top of the spar. Easier to say than do. At first I tried a portable band sander but it is too aggressive. The best wat to do this is with a file and sand paper wrapped around a wood block. And patience… Careful though, the edge becomes very sharp.
Dimpling the holes is an easy job. Just need to be careful not to punch a hole through.
The combination of tools used to smooth out the thin edges
