The spar arrives with all the AN3 bolts for rib attachment installed, so the first job is to remove these and stow away safely until later. Once this is done, the ribs are clecoed to the spar, being VERY careful to place the ribs in the correct places … the drawings show which direction the various rib flanges should point.
Match Drilling AN3 Bolt Holes
I clamped a wood block across the rib flanges to prevent them flexing whilst match drilling.
And then used a cordless drill to bore the #12 holes. No problem with keeping everything perpendicular on the thicker step bar portions, but more care needed on the thinner parts of the step bars since there was less bar depth to align the drill bit.
Final Drilling the #30 & #40 holes
Then I used a #30 reamer to final drill the holes for the AN470AD4 rivets.
And a #40 reamer for the top & bottom AN426AD3 rivet holes.
Marking
I annotated one of the wing rib layout drawings in the manual with L1, R1 etc and then marked the spar & ribs to ensure each rib will find its home after painting.