This picture reminds of the many
steps required when doing dimpled
flush rivet skins.
After the holes are drilled they
are each carefully deburred.
Then they are dimpled with dimpling
tools. My wooden rivet tool also
does a good job dimpling those large
skins. Then the frames, Ls longerons
etc are dimpled or counter sunk,
then everthing is deburred again,
then scotch brighted, degreased,
primed, reclecoed, and finally
riveted.